344 Citations
Aconitate decarboxylase an enzyme member of the MmgE-PrpD family of proteins has gained significant attention in the last decade as a therapeutic target for cancer and inflammatory diseases Its product itaconate is a multifunctional metabolite shown to drive several disease states Though extensively studied in cellulo and in vivo this protein is biochemically and mechanistically under characterized and although a family of inhibitors has been described no ligand-bound structures have yet been determined In this work we present a thorough structural investigation that yielded the first ligand-bound structure of this protein family which required the generation of artifact-free apo crystals ... More
Aconitate decarboxylase 1, an enzyme member of the MmgE-PrpD family of proteins, has gained significant attention in the last decade as a therapeutic target for cancer and inflammatory diseases. Its product, itaconate, is a multifunctional metabolite shown to drive several disease states. Though extensively studied in cellulo and in vivo, this protein is biochemically and mechanistically under characterized and although a family of inhibitors has been described, no ligand-bound structures have yet been determined. In this work we present a thorough structural investigation that yielded the first ligand-bound structure of this protein family, which required the generation of artifact-free apo crystals. We also developed a novel, low-consumption, robust kinetic assay and investigated active site and allosteric mutants to further elucidate structural and dynamic activity relationships of this protein. Less
Fc RIIa encoded by FCGR A is a widely expressed Fc receptor implicated in autoimmunity and infectious disease susceptibility To fine-map the rheumatoid arthritis RA association at the complex FCGR locus we combined gene-specific resequencing genetic association studies in UK and Spanish European cohorts functional genomics structural biology biophysical analyses and cellular assays We identified a common European FCGR A haplotype A defined by Q W H H and the RA-associated SNP rs which showed the strongest association with RA Multi-omics analyses demonstrated that A is associated with reduced expression of the soluble FCGR A splice variant and lower circulating ... More
FcγRIIa, encoded by FCGR2A, is a widely expressed Fc receptor implicated in autoimmunity and infectious disease susceptibility. To fine-map the rheumatoid arthritis (RA) association at the complex FCGR locus, we combined gene-specific resequencing, genetic association studies in UK and Spanish European cohorts, functional genomics, structural biology, biophysical analyses, and cellular assays. We identified a common European FCGR2A haplotype (2A.3), defined by Q27W, H131H, and the RA-associated SNP rs12746613, which showed the strongest association with RA. Multi-omics analyses demonstrated that 2A.3 is associated with reduced expression of the soluble FCGR2A splice variant and lower circulating soluble FcγRIIa levels. Functional studies revealed altered IgG interactions and delayed FcγRIIa signal transduction associated with Q27W, while structural analyses found no evidence for stable ectodomain dimerisation. Together, these findings identify 2A.3 as an important functional contributor to RA susceptibility and provide mechanistic insight into how FCGR2A variation may influence immune regulation and disease risk in Europeans. Less
Four I domain-containing integrins and have evolved to recognize various members of the collagen family A defining structural feature of these receptors is the presence of the C helix within their I domains Glu Arg in the I domain a structure solely found in collagen-binding integrins whose functional mechanism has remained unclear To elucidate the functional role of the C helix and to assess the contribution of the mechanistically important Arg -Glu ion pair in I domain activation we created two variants IR A and IE A Functional solid-phase binding assays and surface plasmon resonance revealed that these variants exhibit ... More
Four αI domain-containing integrins (α1β1, α2β1, α10β1, and α11β1) have evolved to recognize various members of the collagen family. A defining structural feature of these receptors is the presence of the αC helix within their αI domains (Glu284–Arg288 in the α2I domain), a structure solely found in collagen-binding integrins, whose functional mechanism has remained unclear. To elucidate the functional role of the αC helix, and to assess the contribution of the mechanistically important Arg288-Glu318 ion pair in α2I domain activation, we created two variants α2IR288A and α2IE318A. Functional solid-phase binding assays and surface plasmon resonance revealed that these variants exhibit strikingly increased avidity for collagens I and IV, whereas affinities for triple-helical GFOGER peptides, representing a single binding motif, were only slightly increased. The variants displayed distinct ligand-binding profiles, including differences in association and dissociation constants. To understand these differences at a structural level, we determined four novel X-ray crystal structures of the variants, including both ligand-free and ligand-bound (succinic acid or malic acid) states. These structures revealed differences in the folding of the αC helix region, suggesting that its conformation regulates α2I domain activation and ligand specificity, consistent with our binding assays. Additionally, the structures captured the movements of the catalytic metal ion in the metal ion dependent adhesion site, providing a detailed view of the sophisticated activation mechanism of the α2I domain. Less
Interactions between plants and pathogens drive long-term co-evolution through cycles of effector diversification and immune recognition Effectors play central roles in this molecular interplay and zinc-binding folds have been identified in a subset of pathogen effectors yet the contribution of zinc coordination to effector stability and immune recognition remains unclear Here we investigated the structure and recognition of the AvrSr effector from the wheat stem rust fungus Puccinia graminis f sp tritici Pgt Structural and biochemical analyses show that AvrSr adopts a fold containing two zinc-binding sites Transient expression assays in Nicotiana benthamiana show that AvrSr directly interacts with Sr ... More
Interactions between plants and pathogens drive long-term co-evolution through cycles of effector diversification and immune recognition. Effectors play central roles in this molecular interplay, and zinc-binding folds have been identified in a subset of pathogen effectors, yet the contribution of zinc coordination to effector stability and immune recognition remains unclear.
Here, we investigated the structure and recognition of the AvrSr33 effector from the wheat stem rust fungus (Puccinia graminis f. sp. tritici, Pgt). Structural and biochemical analyses show that AvrSr33 adopts a fold containing two zinc-binding sites.
Transient expression assays in Nicotiana benthamiana show that AvrSr33 directly interacts with Sr33, and comparison of recognised and non-recognised AvrSr33 variants identifies a polymorphic loop associated with recognition. This loop is positioned adjacent to one of the zinc-binding sites with its orientation constrained by zinc coordination. Reciprocal mutations of key surface residues within this region alter recognition, whereas mutation of the zinc-binding site abolishes recognition.
Our data suggest that zinc coordination in AvrSr33 provides a structurally constrained scaffold that supports the surface features associated with Sr33 recognition. These findings provide a mechanistic framework for understanding how zinc coordination contributes to effector recognition and may influence the evolutionary trajectories of pathogen effectors. Less
Here, we investigated the structure and recognition of the AvrSr33 effector from the wheat stem rust fungus (Puccinia graminis f. sp. tritici, Pgt). Structural and biochemical analyses show that AvrSr33 adopts a fold containing two zinc-binding sites.
Transient expression assays in Nicotiana benthamiana show that AvrSr33 directly interacts with Sr33, and comparison of recognised and non-recognised AvrSr33 variants identifies a polymorphic loop associated with recognition. This loop is positioned adjacent to one of the zinc-binding sites with its orientation constrained by zinc coordination. Reciprocal mutations of key surface residues within this region alter recognition, whereas mutation of the zinc-binding site abolishes recognition.
Our data suggest that zinc coordination in AvrSr33 provides a structurally constrained scaffold that supports the surface features associated with Sr33 recognition. These findings provide a mechanistic framework for understanding how zinc coordination contributes to effector recognition and may influence the evolutionary trajectories of pathogen effectors. Less
Pyrophosphate-dependent phosphofructokinases provide an alternative route through central carbon metabolism by using inorganic pyrophosphate rather than ATP to phosphorylate fructose- -phosphate These enzymes are absent from mammals but occur in several anaerobic and parasitic organisms where they may support metabolic flexibility and represent potential therapeutic vulnerabilities Here we report three crystal structures of Trichomonas vaginalis PPi-dependent phosphofructokinase TvPPi-PFK a cytosolic enzyme that contributes substantially to parasite glycolytic flux The structures show that TvPPi-PFK adopts the conserved two-domain PFK fold assembles as a tetramer and preserves the canonical PPi MgPPi -binding motifs required for pyrophosphate-dependent catalysis Mass photometry confirms that TvPPi-PFK ... More
Pyrophosphate-dependent phosphofructokinases provide an alternative route through central carbon metabolism by using inorganic pyrophosphate rather than ATP to phosphorylate fructose-6-phosphate. These enzymes are absent from mammals but occur in several anaerobic and parasitic organisms, where they may support metabolic flexibility and represent potential therapeutic vulnerabilities. Here, we report three crystal structures of Trichomonas vaginalis PPi-dependent phosphofructokinase 1 (TvPPi-PFK), a cytosolic enzyme that contributes substantially to parasite glycolytic flux. The structures show that TvPPi-PFK adopts the conserved two-domain PFK fold, assembles as a tetramer, and preserves the canonical PPi/MgPPi²⁻-binding motifs required for pyrophosphate-dependent catalysis. Mass photometry confirms that TvPPi-PFK is predominantly tetrameric in solution and shows that nucleotide- and Mg²⁺/PPi-containing conditions further stabilize the tetrameric assembly. Unexpectedly, the ligand-bound structures reveal ATP, AMP, and sugar-phosphate ligands at a recurring dimer-interface site that is spatially distinct from the canonical PPi/MgPPi²⁻ catalytic donor-binding pocket. This non-canonical interface is more accessible in TvPPi-PFK than in available PPi-PFK structures, suggesting a previously unrecognized ligand-recognition feature. These findings expand the structural landscape of the PFK superfamily and provide a framework for testing how nucleotide and sugar-phosphate binding may influence TvPPi-PFK function, regulation, and future antitrichomonal drug-discovery efforts. Less
Chemical topology has emerged as a unique dimension in protein engineering motivating the pursuit of topologically nontrivial protein architectures for functional advantages such as enhanced stability and rich dynamics However the structural diversity of artificial mechanically interlocked proteins remains limited Here we report the computational design and cellular synthesis of a pair of topological isomers via symmetric assembly of orthogonal entangling motifs By fusing two C symmetric entangling motifs i e p dim and HP in specific arrangements we programmed the formation of multiple crossings which upon cyclization yielded a protein Solomon link and a protein three-twist knot The fusion ... More
Chemical topology has emerged as a unique dimension in protein engineering, motivating the pursuit of topologically nontrivial protein architectures for functional advantages, such as enhanced stability and rich dynamics. However, the structural diversity of artificial mechanically interlocked proteins remains limited. Here, we report the computational design and cellular synthesis of a pair of topological isomers via symmetric assembly of orthogonal entangling motifs. By fusing two C2 symmetric entangling motifs, i.e., p53dim and HP0242, in specific arrangements, we programmed the formation of multiple crossings, which upon cyclization yielded a protein Solomon link and a protein three-twist knot. The fusion patterns and linker lengths were systematically optimized to direct the formation of the intended topologies. Their successful cellular synthesis was validated through biophysical and structural analyses, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis, size exclusion chromatography, and liquid chromatography-mass spectrometry. Notably, we report the crystal structure of an artificial protein three-twist knot. Both the Solomon link and the three-twist knot displayed increased structural compactness and stability relative to their controls with lower topological complexity (e.g., Hopf link, trefoil knot, and linear forms), as evidenced by their superior thermal stability and resistance to chemical denaturation. This modular design strategy provides a rational and extensible route to diverse mechanically interlocked proteins and could be generalized to access even more complex architectures, such as protein chainmail-like nanocages and woven protein frameworks. Less
Structural biology has fundamentally influenced pharmaceutical research and development at Merck Sharp Dohme LLC Rahway New Jersey USA progressing from pioneering macromolecular crystallography in the s to a fully integrated platform that today encompasses X-ray crystallography cryo-electron microscopy micro-electron diffraction and cryo-electron tomography In this review we present a comprehensive overview of how these complementary methods have advanced drug discovery across diverse therapeutic areas We illustrate how atomic to cellular structural insights inform drug discovery and development from target identification and validation hit finding lead identification through lead optimization and clinical progression Furthermore we describe how structural biology techniques aid ... More
Structural biology has fundamentally influenced pharmaceutical research and development at Merck Sharp & Dohme LLC, Rahway, New Jersey, USA, progressing from pioneering macromolecular crystallography in the 1980s to a fully integrated platform that today encompasses X-ray crystallography, cryo-electron microscopy, micro-electron diffraction and cryo-electron tomography. In this review, we present a comprehensive overview of how these complementary methods have advanced drug discovery across diverse therapeutic areas. We illustrate how atomic to cellular structural insights inform drug discovery and development, from target identification and validation, hit finding, lead identification through lead optimization and clinical progression. Furthermore, we describe how structural biology techniques aid in formulation strategies of antibodies and vaccines. Finally, we highlight the growing integration of ex situ and in situ approaches as a paradigm shift towards elucidating drug mechanisms in native cellular contexts, a transition poised to accelerate the discovery and development of next-generation therapeutics. Less
TL A is a proinflammatory cytokine in the tumor necrosis factor TNF superfamily that signals via DR on T helper cells innate lymphoid cells and fibroblasts Dysregulated TL A signaling has been hypothesized to affect multiple immune-mediated diseases with clinical proof of concept demonstrated in ulcerative colitis and Crohn s disease We characterized the binding affinity specificity structure pharmacodynamics pharmacokinetics and toxicity profiles of SPY and SPY two novel extended half-life monoclonal antibodies that inhibit TL A SPY and SPY demonstrated selective high-affinity binding to human TL A KD pM and potent functional inhibition of DR signaling Based on Fc ... More
TL1A is a proinflammatory cytokine in the tumor necrosis factor (TNF) superfamily that signals via DR3 on T helper cells, innate lymphoid cells, and fibroblasts. Dysregulated TL1A signaling has been hypothesized to affect multiple immune-mediated diseases, with clinical proof of concept demonstrated in ulcerative colitis and Crohn’s disease. We characterized the binding affinity, specificity, structure, pharmacodynamics, pharmacokinetics, and toxicity profiles of SPY002 and SPY072, two novel extended half-life monoclonal antibodies that inhibit TL1A. SPY002 and SPY072 demonstrated selective, high-affinity binding to human TL1A (KD ≈ 31–35 pM) and potent functional inhibition of DR3 signaling. Based on Fc modifications, SPY002 and SPY072 showed attenuated Fc effector function and increased FcRn binding at acidic pH (5.8). Both antibodies exhibited enhanced PK profiles in nonhuman primates, resulting in predicted human half-lives that support quarterly or biannual dosing. In toxicity studies, no drug-related adverse effects were observed with either antibody at exposures >10 times those anticipated in clinical trials. In a rat collagen-induced arthritis model, anti-TL1A antibody treatment effectively reduced arthritis severity, with similar efficacy to the TNF antagonist etanercept. In humanized mouse Imiquimod-induced psoriasis and 2,4,6‑trinitrobenzene sulfonic acid colitis models, anti-TL1A demonstrated similar efficacy to anti–IL-23 and anti-TNF antibodies. These findings characterize two novel extended half-life TL1A antibodies and support the ongoing Phase 2 clinical development of SPY002 and SPY072 for immune-mediated diseases such as inflammatory bowel disease and rheumatic diseases. Less
Background Calcium-dependent protein kinase CDPK has emerged as a protozoan specific target for the treatment of cryptosporidiosis A previous study identified pyridopyrimidinones as new Cryptosporidium parvum Cp CDPK inhibitors with potent growth inhibition against C parvum and C hominis Docking analyses suggested the unique positioning of the kinase s Chelix could present refinement opportunities Methods Compounds designed to optimize the pyridopyrimidinones focused on the back-pocket region predicted to be proximal to the C-helix the solvent exposed region and the ATP ribose-binding site Designed derivatives were synthesized and assessed for CpCDPK and Src kinase inhibition and for Cryptosporidium spp growth inhibition ... More
Background: Calcium-dependent protein kinase 1 (CDPK1) has emerged as a protozoan specific
target for the treatment of cryptosporidiosis. A previous study identified pyridopyrimidinones as
new Cryptosporidium parvum (Cp) CDPK1 inhibitors with potent growth inhibition against C.
parvum and C. hominis. Docking analyses suggested the unique positioning of the kinase’s αChelix could present refinement opportunities.
Methods: Compounds designed to optimize the pyridopyrimidinones focused on the back-pocket region predicted to be proximal to the αC-helix, the solvent exposed region and the ATP ribose-binding site. Designed derivatives were synthesized and assessed for CpCDPK1 and Src kinase inhibition and for Cryptosporidium spp., growth inhibition in mammalian cells. AMP/Mg+2 and three inhibitors were co-crystalized with CpCDPK1, and two inhibitors were profiled for kinase selectivity.
Results: WIN 4-88 was identified with CpCDPK1 (IC50 = 0.056 μM), and growth inhibition of zoonotic C. parvum (NLuc EC50 = 0.042 μM), anthroponotic C. parvum (Tu114 EC50 = 0.030 μM), and C. hominis Tu502 (EC50 = 0.062 μM), as well as enhanced kinome selectivity. The crystal structures confirmed the predicted binding mode, indicating key interactions with hinge residue Y155, similar orientations of the solvent expose moieties, occupancy of the back-pocket near the αC-helix and for one inhibitor containing a solubilizing hydroxyethyl attached to the central heterocycle extension into the ATP ribose-binding site.
Conclusions: The expanded structure-activity relationship and structural insights will potentially be applicable to other chemotypes with similar binding modes and will enhance development of CpCDPK1 inhibitors for the treatment of cryptosporidiosis. Less
target for the treatment of cryptosporidiosis. A previous study identified pyridopyrimidinones as
new Cryptosporidium parvum (Cp) CDPK1 inhibitors with potent growth inhibition against C.
parvum and C. hominis. Docking analyses suggested the unique positioning of the kinase’s αChelix could present refinement opportunities.
Methods: Compounds designed to optimize the pyridopyrimidinones focused on the back-pocket region predicted to be proximal to the αC-helix, the solvent exposed region and the ATP ribose-binding site. Designed derivatives were synthesized and assessed for CpCDPK1 and Src kinase inhibition and for Cryptosporidium spp., growth inhibition in mammalian cells. AMP/Mg+2 and three inhibitors were co-crystalized with CpCDPK1, and two inhibitors were profiled for kinase selectivity.
Results: WIN 4-88 was identified with CpCDPK1 (IC50 = 0.056 μM), and growth inhibition of zoonotic C. parvum (NLuc EC50 = 0.042 μM), anthroponotic C. parvum (Tu114 EC50 = 0.030 μM), and C. hominis Tu502 (EC50 = 0.062 μM), as well as enhanced kinome selectivity. The crystal structures confirmed the predicted binding mode, indicating key interactions with hinge residue Y155, similar orientations of the solvent expose moieties, occupancy of the back-pocket near the αC-helix and for one inhibitor containing a solubilizing hydroxyethyl attached to the central heterocycle extension into the ATP ribose-binding site.
Conclusions: The expanded structure-activity relationship and structural insights will potentially be applicable to other chemotypes with similar binding modes and will enhance development of CpCDPK1 inhibitors for the treatment of cryptosporidiosis. Less
Insomnia is a widespread sleep disorder that significantly impairs quality of life and imposes a societal burden Although benzodiazepines and Z-drugs are commonly used for treating insomnia these drugs often have side effects such as excessive muscle relaxation and dependency The orexin signaling pathway has emerged as a promising therapeutic target for insomnia with dual orexin receptor antagonists DORAs offering an alternative approach to treatment To reduce the potential of these drugs for next-day residual effects we developed vornorexant a novel DORA with a high receptor affinity and a short elimination half-life In this study we investigated the molecular interactions ... More
Insomnia is a widespread sleep disorder that significantly impairs quality of life and imposes a societal burden. Although benzodiazepines and Z-drugs are commonly used for treating insomnia, these drugs often have side effects, such as excessive muscle relaxation and dependency. The orexin signaling pathway has emerged as a promising therapeutic target for insomnia, with dual orexin receptor antagonists (DORAs) offering an alternative approach to treatment. To reduce the potential of these drugs for next-day residual effects, we developed vornorexant, a novel DORA with a high receptor affinity and a short elimination half-life. In this study, we investigated the molecular interactions of this drug with human orexin receptors through crystal structure analysis of its binding to orexin type 2 receptor (OX2R) and a docking simulation of the drug with orexin type 1 receptor (OX1R). The crystal structure of the OX2R–vornorexant complex revealed a conserved U-shaped conformation stabilized by hydrophobic and hydrogen-bonding interactions, including key contacts with Asn324, His350 and Pro131. OX1R–vornorexant docking simulations indicated a similar binding mode to OX1R, with no steric hindrance observed, supporting a balanced dual antagonism. These results provide a structural basis for the high-affinity dual antagonism of vornorexant and offer insights for the design of orexin receptor antagonists. Less
The precise and selective transport of protons across cellular membranes relies on the dynamic formation and dissipation of hydrogen-bonding networks involving water molecules protein sidechains and backbone carbonyls As in aqueous solution protons are conducted over long distances along chains of hydrogen-bonded water molecules within narrow protein pores To engineer proton-conductive pathways therefore we must explicitly account for the dynamic behavior of these networks In previous work we showed that incorporation of polar Gln residues into hydrophobic pores drives formation of transient single-file water wires that enable proton-selective transport Here we sought to enhance conduction by introducing targeted Ile-to-Ser substitutions ... More
The precise and selective transport of protons across cellular membranes relies on the dynamic formation and dissipation of hydrogen-bonding networks involving water molecules, protein sidechains, and backbone carbonyls. As in aqueous solution, protons are conducted over long distances along chains of hydrogen-bonded water molecules within narrow protein pores. To engineer proton-conductive pathways, therefore, we must explicitly account for the dynamic behavior of these networks. In previous work, we showed that incorporation of polar Gln residues into hydrophobic pores drives formation of transient, single-file water wires that enable proton-selective transport. Here, we sought to enhance conduction by introducing targeted Ile-to-Ser substitutions to extend connectivity across the pore. We find that the position of Ser relative to Gln modulates sidechain dynamics and, in turn, channel hydration. Although increased polarity reduces hydrophobic length and enhances hydration, these effects alone do not explain the observed conduction rates. Instead, asymmetry in the arrangement and dynamics of polar sidechains emerges as a key determinant of proton conductivity. Together, these results demonstrate that proton conduction is governed not only by pore polarity and hydration, but also by the dynamic and asymmetric organization of hydrogen-bonding networks. This work establishes design principles for engineering proton-selective channels and reveals how asymmetry enables efficient proton transport across biological membranes. Less
Constant changes in SARS-CoV- in human populations as well as potential future spillovers from animal coronaviruses have provided the impetus for the development of additional direct-acting antivirals We describe herein the discovery of a new class of broad-spectrum inhibitors of coronavirus C-like protease CLpro a cysteine protease essential for viral replication and a validated drug target that incorporate in their structure a -oxazaphospholidin- -one scaffold Inhibitors and were found to have EC values of and nM against SARS-CoV- CLpro respectively and CC values M These compounds also potently inhibited MERS-CoV CLpro IC nM and nM respectively Importantly several of the ... More
Constant changes in SARS-CoV-2 in human populations as well as potential future spillovers from animal coronaviruses have provided the impetus for the development of additional direct-acting antivirals. We describe herein the discovery of a new class of broad-spectrum inhibitors of coronavirus 3C-like protease (3CLpro), a cysteine protease essential for viral replication and a validated drug target, that incorporate in their structure a 1,3,2-oxazaphospholidin-3-one scaffold. Inhibitors 1 and 2 were found to have EC50 values of 60 and 50 nM against SARS-CoV-2 3CLpro, respectively, and CC50 values >100 µM. These compounds also potently inhibited MERS-CoV 3CLpro (IC50 120 nM and 90 nM, respectively). Importantly, several of the synthesized compounds inhibited recombinant human cathepsin L with IC50 values in the low nM to sub-nM range. Thus, the compounds can potentially exhibit high antiviral potency by abrogating viral entry via the inhibition of cathepsin L and viral replication by inhibition of 3CLpro. High resolution cocrystal structures were determined to elucidate the mechanism of action, identify the molecular determinants associated with binding, and to inform the optimization process. Less
Structural analyses of Trichomonas vaginalis pyrophosphate-dependent phosphofructokinase (TvPPi-PFK)
Trichomonas vaginalis causes trichomoniasis the most common non-viral sexually transmitted disease in humans T vaginalis pyrophosphate-dependent phosphofructokinase TvPPi-PFK is a putative target for rational structure-based drug discovery given its absence in mammals and its importance for parasite survival TvPPi-PFK is a cytosolic enzyme that catalyzes the phosphorylation of fructose- -phosphate using pyrophosphate PPi as the phosphoryl donor This reversible reaction catalyzed by TvPPi-PFK is the first committed step in glycolysis Its reverse reaction is vital for gluconeogenesis in T vaginalis The purification crystallization structure determination and preliminary structure-functional analyses of three crystal structures of TvPPi-PFK are presented All three structures ... More
Trichomonas vaginalis causes trichomoniasis, the most common non-viral sexually transmitted disease in humans. T. vaginalis pyrophosphate-dependent phosphofructokinase (TvPPi-PFK) is a putative target for rational, structure-based drug discovery, given its absence in mammals and its importance for parasite survival. TvPPi-PFK is a cytosolic enzyme that catalyzes the phosphorylation of fructose-6-phosphate using pyrophosphate (PPi) as the phosphoryl donor. This reversible reaction, catalyzed by TvPPi-PFK, is the first committed step in glycolysis. Its reverse reaction is vital for gluconeogenesis in T. vaginalis. The purification, crystallization, structure determination, and preliminary structure-functional analyses of three crystal structures of TvPPi-PFK are presented. All three structures organize as tetramers with the conserved motifs essential for pyrophosphate binding and PPi-PFK catalytic activity. Comparative analysis with structural neighbors from other organisms demonstrated that despite sharing <29% sequence identity, TvPPi-PFK’s protomer shares overall topology with both PPi- and ATP-dependent PFKs. Mass photometry confirmed that TvPPi-PFK formed tetramers under near-physiological conditions. Unexpectedly, TvPPi-PFK crystals dephosphorylate ATP to AMP during soaking. In all three structures, either ATP or AMP is bound at the enzyme’s dimer interface, typical of ATP-PFKs, but a novel finding for PPi-PFKs. Furthermore, a sugar phosphate binding site was observed in proximity to the ATP-binding site. Thus, the three reported TvPPi-PFK structures validate its established PPi-dependent activity while revealing previously unreported ATP and sugar phosphate binding. This study also lays a foundation for future research into putative ATP-dependent activity of TvPPi-PFK and for evaluating known phosphofructokinase inhibitors as potential therapeutics for trichomoniasis. These findings expand our understanding of PFK superfamily diversity and support the continued exploration of TvPPi-PFK as a drug target for trichomoniasis Less
The ToxRS system belongs to a family of co-component transmembrane transcription regulators that act as sensors of environmental cues and regulate virulence gene expression in several bacterial pathogens These systems are thought to operate by sensing environmental stimuli and transmitting signals through periplasmic domains to activate DNA-binding transcription factors In the enteric pathogens Vibrio parahaemolyticus and Vibrio cholerae the ToxRS system regulates virulence factors responsible for severe gastrointestinal symptoms in humans ToxR is a DNA-binding regulator associated in the periplasm with ToxS a protein of poorly understood function ToxS modulates the activity of its binding partner ToxR in the presence ... More
The ToxRS system belongs to a family of co-component transmembrane transcription regulators that act as sensors of environmental cues and regulate virulence gene expression in several bacterial pathogens. These systems are thought to operate by sensing environmental stimuli and transmitting signals through periplasmic domains to activate DNA-binding transcription factors. In the enteric pathogens Vibrio parahaemolyticus and Vibrio cholerae, the ToxRS system regulates virulence factors responsible for severe gastrointestinal symptoms in humans. ToxR is a DNA-binding regulator associated in the periplasm with ToxS, a protein of poorly understood function. ToxS modulates the activity of its binding partner ToxR in the presence of bile salts, antimicrobial cholesterol metabolites secreted into the gut. To date, the molecular mechanism underlying this regulation remains unclear. We present crystal structures of the V. parahaemolyticus ToxS periplasmic domain (ToxSp) with and without the bile salt glycocholate. ToxSp forms an 8-stranded broken β-barrel with a central α-helix and is structurally homologous to a group of chaperone proteins. ToxSp has a highly conserved hydrophobic core that stabilizes the β-barrel fold, while the binding pocket tolerates substantial variation, consistent with binding hydrophobic ligands. Strikingly, we discovered that Vp-ToxSp binds three molecules of glycocholate and the presence of this bile salt leads to the formation a strand-swapped ToxS homodimer. Finally, modeling two ToxR periplasmic domains in complex with the glycocholate-bound ToxSp homodimer provides a structure-based model for bile salt-mediated heterotetramerization of the ToxRS system. Overall, our study addresses a major longstanding question in the field of Vibrio virulence regulation providing a scenario that could apply to other pathogens that utilize these membrane-bound family transcriptional regulators. Less
Recoverin is a key calcium sensor that controls the desensitization of the visual rhodopsin by GRK Previous studies have traditionally been conducted on bovine protein bRec while data on human ortholog hRec remain scarce Here we combine X-ray crystallography Xray absorption spectroscopy XANES quantum mechanical calculations molecular dynamics and functional assays to provide an integrated characterization of hRec The Ca -bound hRec structure was solved at showing that unlike bRec hRec interacts with ROS membranes at physiologically relevant submicromolar Ca levels due to a speciesspecific charge distribution that might influence membrane interactions Both recoverins form a set of Ca Zn ... More
Recoverin is a key calcium sensor that controls the desensitization of the visual rhodopsin
by GRK1. Previous studies have traditionally been conducted on bovine protein (bRec), while
data on human ortholog (hRec) remain scarce. Here, we combine X-ray crystallography, Xray absorption spectroscopy (XANES), quantum mechanical calculations, molecular
dynamics, and functional assays to provide an integrated characterization of hRec. The
2Ca2+-bound hRec structure was solved at 1.60 Å, showing that, unlike bRec, hRec interacts
with ROS membranes at physiologically relevant submicromolar Ca2+ levels, due to a speciesspecific charge distribution that might influence membrane interactions. Both recoverins
form a set of Ca2+/Zn2+-bound conformers with improved functional performance. X-ray
crystallography (1.85 Å) and XANES revealed a specific tetrahedral Zn2+ site in 1Ca2+-bound
hRec, the first such site reported in the NCS family. In 1Ca2+-bound hRec, zinc promotes the
formation of active state, whereas in 2Ca2+-state of bRec, it significantly enhances GRK1
binding, as the latter can complement the Zn2+ coordination. These data refine our
understanding of recoverin function in humans and highlight its role as a key link between
calcium and zinc signaling in mammalian photoreceptors under normal and pathological
conditions. Less
by GRK1. Previous studies have traditionally been conducted on bovine protein (bRec), while
data on human ortholog (hRec) remain scarce. Here, we combine X-ray crystallography, Xray absorption spectroscopy (XANES), quantum mechanical calculations, molecular
dynamics, and functional assays to provide an integrated characterization of hRec. The
2Ca2+-bound hRec structure was solved at 1.60 Å, showing that, unlike bRec, hRec interacts
with ROS membranes at physiologically relevant submicromolar Ca2+ levels, due to a speciesspecific charge distribution that might influence membrane interactions. Both recoverins
form a set of Ca2+/Zn2+-bound conformers with improved functional performance. X-ray
crystallography (1.85 Å) and XANES revealed a specific tetrahedral Zn2+ site in 1Ca2+-bound
hRec, the first such site reported in the NCS family. In 1Ca2+-bound hRec, zinc promotes the
formation of active state, whereas in 2Ca2+-state of bRec, it significantly enhances GRK1
binding, as the latter can complement the Zn2+ coordination. These data refine our
understanding of recoverin function in humans and highlight its role as a key link between
calcium and zinc signaling in mammalian photoreceptors under normal and pathological
conditions. Less
UreE is a nickel chaperone that is required for the safe and efficient delivery of nickel to the active site of the metalloenzyme urease which is a key virulence factor of the urinary-tract pathogen Proteus mirabilis We investigated the structural features of P mirabilis UreE PmUreE using protein X-ray crystallography and its nickel-binding capacity by inductively coupled plasma mass spectrometry Here we report a resolution crystal structure of homodimeric PmUreE and show that it has the capacity to bind five Ni II ions per dimer Truncation of the histidine-rich C-terminus reduced the nickel-binding capacity by two Ni II ions per ... More
UreE is a nickel chaperone that is required for the safe and efficient delivery of nickel to the active site of the metalloenzyme urease, which is a key virulence factor of the urinary-tract pathogen Proteus mirabilis. We investigated the structural features of P. mirabilis UreE (PmUreE) using protein X-ray crystallography and its nickel-binding capacity by inductively coupled plasma mass spectrometry. Here, we report a 2.0 Å resolution crystal structure of homodimeric PmUreE and show that it has the capacity to bind five Ni(II) ions per dimer. Truncation of the histidine-rich C-terminus reduced the nickel-binding capacity by two Ni(II) ions per dimer, and comparison with homologous UreE structures allowed the assignment of putative nickel-binding sites within the PmUreE structure. These findings increase our understanding of how PmUreE binds nickel and ultimately prevents this toxic metal from causing significant cellular damage in P. mirabilis. Less
Safe and effective vaccines against co-circulating mosquito-borne orthoflaviviruses such as Zika virus ZikV and the four serotypes of Dengue virus DenV - must elicit broadly neutralizing antibodies bnAbs to prevent the risk of enhancement of infection by non-neutralizing antibodies We recently discovered new orthoflavivirus-directed bnAbs including F S which neutralizes DenV - and ZikV with comparable or superior potency to the previously characterized E dimer epitope EDE bnAbs Here we used cryoEM and X-ray crystallography to understand the basis of cross-neutralization of F S at the molecular level We obtained a cryoEM structure of F S Fab bound to a ... More
Safe and effective vaccines against co-circulating mosquito-borne orthoflaviviruses such as Zika virus (ZikV) and the four serotypes of Dengue virus (DenV1-4) must elicit broadly neutralizing antibodies (bnAbs) to prevent the risk of enhancement of infection by non-neutralizing antibodies. We recently discovered new orthoflavivirus-directed bnAbs, including F25.S02, which neutralizes DenV1-4 and ZikV with comparable or superior potency to the previously characterized E dimer epitope (EDE) bnAbs. Here, we used cryoEM and X-ray crystallography to understand the basis of cross-neutralization of F25.S02 at the molecular level. We obtained a ~ 4.2 Å cryoEM structure of F25.S02 Fab bound to a stabilized DenV3 soluble E protein dimer and a 2.3 Å crystal structure of F25.S02 Fab bound to ZikV soluble E protein dimer. Like previously described EDE1 bnAbs, the structural epitope of F25.S02 is at the E dimer interface, encompassing predominantly conserved regions in domain II, including the fusion loop. However, unlike EDE1 bnAbs, F25.S02 binding is almost entirely dependent on the heavy chain and is shifted slightly away from the dimer symmetry axis. Our findings emphasize the importance of this cross-neutralizing site of vulnerability for DenV and ZikV that can facilitate rational design of vaccines and therapeutics. Less
-Hemolysin Ahly is a major Staphylococcus aureus virulence determinant implicated in tissue injury and immune dysregulation antibody inhibitors have reached clinical trials but alternatives with improved ease of manufacture and tissue penetration are desirable Here we demonstrate that phage-derived bicyclic peptides can serve as compact chemically tractable Ahly neutralisers Using TATB-scaffolded M phage libraries we identified WNP-motif containing bicyclic binders with a lead hit of Peptide KD nM and progressed the lead by iterative affinity maturation to Peptide KD nM and by incorporation of strategically chosen non-canonical amino acids to yield Peptide KD nM A co-crystal structure with AhlyH A ... More
α-Hemolysin (Ahly) is a major Staphylococcus aureus virulence determinant implicated in tissue injury and immune dysregulation; antibody inhibitors have reached clinical trials but alternatives with improved ease of manufacture and tissue penetration are desirable. Here we demonstrate that phage-derived bicyclic peptides can serve as compact, chemically tractable Ahly neutralisers. Using TATB-scaffolded M13 phage libraries we identified WNP-motif containing bicyclic binders, with a lead hit of Peptide 14 (KD = 1792nM) and progressed the lead by iterative affinity maturation to Peptide 20 (KD = 609 nM) and by incorporation of strategically chosen non-canonical amino acids to yield Peptide 88 (KD = 96 nM). A 2.2 Å co-crystal structure with AhlyH35A locates the binding footprint on the rim domain and explains the critical role of the WNP motif in target engagement. Functional assays show that the Peptide 88 blocks Ahly mediated hemolysis, inhibits Ahly driven ADAM10 activation, and elucidate its inhibitory mechanism of preventing Ahly binding to human A549 epithelial cells. Peptide 88 protects A549 cells from recombinant toxin and attenuates cytotoxicity in S. aureus co-culture experiments, whilst showing no toxicity to A549 cells. Bicyclic peptides thus represent a new and promising anti-virulence modality: small, synthetically accessible molecules that mimic antibody recognition, with therapeutic potential against S. aureus infections. Less
Complement and pathogenic antibodies act independently and together to mediate the pathology of many autoimmune diseases To address these drivers of disease we generated a monoclonal antibody mAb CSL that binds and inhibits both complement and the neonatal Fc fragment crystallizable receptor FcRn The fragment antigen binding Fab portion of CSL was engineered to bind both human C huC zymogen and the active fragment huC b to inhibit the classical and lectin complement pathways in vitro and C b deposition on primary lung endothelial cells using a -dimensional microvascular model system Engineering of a triple amino acid mutation YPY motif ... More
Complement and pathogenic antibodies act independently and together to mediate the pathology of many autoimmune diseases. To address these drivers of disease, we generated a monoclonal antibody (mAb), CSL305, that binds and inhibits both complement and the neonatal Fc (fragment crystallizable) receptor FcRn. The fragment antigen binding (Fab) portion of CSL305 was engineered to bind both human C2 (huC2) zymogen and the active fragment huC2b to inhibit the classical and lectin complement pathways in vitro, and C3b deposition on primary lung endothelial cells using a 3-dimensional microvascular model system. Engineering of a triple amino acid mutation (“YPY” motif) into the Fc region of CSL305 increased its affinity to FcRn at both acidic and neutral pH, allowing it to also act as a potent FcRn antagonist. Intracellular trafficking experiments demonstrated that CSL305, but not the wild-type (WT) mAb lacking the YPY motif, was able to block immunoglobulin G (IgG) recycling in vitro. The generation of a high resolution 2.6Å crystal structure of CSL305 Fab region bound to huC2b showed that the epitope lies directly over the huC2b catalytic triad, providing evidence of its complement mechanism of action as a neutralising mAb. Early pharmacokinetic (PK)/pharmacodynamic (PD) studies using CSL305 in cynomolgus monkeys demonstrated both complement inhibition and FcRn antagonism in vivo, with reductions in complement classical pathway activity and endogenous IgG observed following single intravenous (IV) administration. CSL305 thus represents a dual-functional mAb as a potential therapeutic candidate. Less
Improving health and quality of life in our society is a key focus of drug development Methods for drug discovery are being optimized in multiple ways to reduce costs and timelines Crystallographic fragment screening CFS is increasingly being employed as an early screening method in drug discovery projects Here we demonstrate that selecting the optimal protein crystal form can significantly impact hit rates Two CFS campaigns are carried out against the two crystal forms of the SARS-CoV- main protease using the same fragment library and an almost identical experimental setup Although both crystal forms exhibit similar diffraction properties the observed ... More
Improving health and quality of life in our society is a key focus of drug development. Methods for drug discovery are being optimized in multiple ways to reduce costs and timelines. Crystallographic fragment screening (CFS) is increasingly being employed as an early screening method in drug discovery projects. Here, we demonstrate that selecting the optimal protein crystal form can significantly impact hit rates. Two CFS campaigns are carried out against the two crystal forms of the SARS-CoV-2 main protease, using the same fragment library and an almost identical experimental setup. Although both crystal forms exhibit similar diffraction properties, the observed hit rates in the two campaigns differ significantly. A hit rate of 3% is determined for the monoclinic crystals, while a hit rate of 16% is observed for the orthorhombic crystals. These findings are consistent with the more open molecular packing in the orthorhombic crystals, where the solvent channels leading to the active sites are approximately twice the size of those in the monoclinic crystal form. Our results highlight the critical importance of the crystal form in a crystallographic screening, identifying it as one of the most important parameters to optimize when preparing a CFS campaign. Less
Light Oxygen Voltage LOV domains are important widespread receptors of blue light that also found applications in optogenetics and imaging While LOV domains from mesophiles are relatively well characterized their counterparts from thermophilic microorganisms remain understudied Here we express two constructs of a LOV domain belonging to a histidine kinase from Meiothermus ruber MrLOV and MrLOVe and show that they are photoactive with recovery time values of and min respectively and thermostable Crystal structures reveal that MrLOV which lacks helices A and J forms a parallel dimer whereas MrLOVe is a tetramer organized as an antiparallel dimer of two parallel ... More
Light Oxygen Voltage (LOV) domains are important widespread receptors of blue light that also found applications in optogenetics and imaging. While LOV domains from mesophiles are relatively well characterized, their counterparts from thermophilic microorganisms remain understudied. Here, we express two constructs of a LOV domain belonging to a histidine kinase from Meiothermus ruber, MrLOV and MrLOVe, and show that they are photoactive, with recovery time values of 21 and 27 min, respectively, and thermostable. Crystal structures reveal that MrLOV, which lacks helices A’α and Jα, forms a parallel dimer, whereas MrLOVe is a tetramer organized as an antiparallel dimer of two parallel dimers interacting via helices Jα. One MrLOVe dimer is symmetric, and the other is asymmetric, with conformational differences mirroring activation-related changes in other LOV domains. Our data provide the structural basis for understanding and engineering of thermophilic LOVs and pave the way for development of thermostable and photostable LOV-derived optogenetic tools and flavin-based fluorescent proteins. Less
Gene expression is governed by dynamic switches between repressive and activating transcriptional states Among the molecules mediating these transitions chromatin readers and transcription factors play pivotal roles However how they assemble with regulatory machineries to enable crosstalk between gene repression and activation remains unknown Here we use an integrative structural dynamics approach combining cryo-EM crosslinking mass spectrometry fragment-resolved protein interactome mapping and crystallography to show how the dual-role chromatin reader Cti and transcription factors Ash and Ume engage the Sin deacetylase complex a major regulatory hub in eukaryotes We find that Cti competes with Ash to drive its dynamic recruitment ... More
Gene expression is governed by dynamic switches between repressive and activating transcriptional states1,2. Among the molecules mediating these transitions, chromatin readers and transcription factors play pivotal roles3,4. However, how they assemble with regulatory machineries to enable crosstalk between gene repression and activation remains unknown. Here, we use an integrative structural dynamics approach – combining cryo-EM, crosslinking mass spectrometry, fragment-resolved protein interactome mapping and crystallography – to show how the dual-role chromatin reader Cti6 and transcription factors Ash1 and Ume6 engage the Sin3 deacetylase complex, a major regulatory hub in eukaryotes5. We find that Cti6 competes with Ash1 to drive its dynamic recruitment to a shared peripheral module, while Ume6 engages the Sin3 scaffold through a defined, minimal interface. Using high-throughput mutational scanning, we reveal deleterious and gain-of-function mutations in Sin3, identifying evolutionarily conserved residues essential for anchoring transcription factors. Together, these results provide structural and functional insights into how dual-role regulators engage the central Sin3 complex, revealing subtle assembly principles that may facilitate crosstalk between gene repression and activation. They also establish an integrative multidisciplinary framework to dissect the dynamics of macromolecular assemblies across biological systems. Less
Epstein-Barr virus EBV causes infectious mononucleosis and contributes to neurodegenerative disorders and malignancies particularly in immune-compromised hosts Transplant patients face high risk of post-transplant lymphoproliferative disease a life-threatening EBV-driven lymphoma There are no EBV-specific vaccines or treatments however neutralizing antibodies against EBV glycoproteins may offer utility as therapeutic agents EBV entry into B cells involves gp which binds complement receptors and gp which engages HLA class II to trigger fusion Most existing monoclonal antibodies mAbs against these antigens are non-human limiting clinical use Using a transgenic mouse model we generate two gp and eight gp genetically human neutralizing mAbs that ... More
Epstein-Barr virus (EBV) causes infectious mononucleosis and contributes to neurodegenerative disorders and malignancies, particularly in immune-compromised hosts. Transplant patients face high risk of post-transplant lymphoproliferative disease, a life-threatening EBV-driven lymphoma. There are no EBV-specific vaccines or treatments; however, neutralizing antibodies against EBV glycoproteins may offer utility as therapeutic agents. EBV entry into B cells involves gp350, which binds complement receptors, and gp42, which engages HLA class II to trigger fusion. Most existing monoclonal antibodies (mAbs) against these antigens are non-human, limiting clinical use. Using a transgenic mouse model, we generate two gp350 and eight gp42 genetically human neutralizing mAbs that block receptor binding. Structural analyses reveal extended sites of vulnerability relevant to vaccine development. Delivery of a gp42 mAb protects humanized mice from EBV challenge, while a gp350 mAb provides partial protection. These mAbs highlight the utility of transgenic mice to produce therapeutic mAbs for preventing EBV-driven disease. Less
HECT E ligases regulate many cellular processes yet how they recognise their substrates and synthesise specific types of poly-ubiquitin chains is still incompletely understood HECTD a member of the other HECT family is implicated in the regulation of inflammation apoptosis and infection and highly expressed in several cancers These functions are largely attributed to its ligase activity and modification of diverse substrates with different types of ubiquitin chains We present a detailed analysis of the ligase activity of HECTD including its ubiquitin linkage preferences oligomeric state and substrate ubiquitination Using cryo-EM we provide the full-length structures of HECTD in both ... More
HECT E3 ligases regulate many cellular processes, yet how they recognise their substrates and synthesise specific types of poly-ubiquitin chains is still incompletely understood. HECTD3, a member of the “other HECT” family, is implicated in the regulation of inflammation, apoptosis, and infection and highly expressed in several cancers. These functions are largely attributed to its ligase activity and modification of diverse substrates with different types of ubiquitin chains. We present a detailed analysis of the ligase activity of HECTD3, including its ubiquitin linkage preferences, oligomeric state and substrate ubiquitination. Using cryo-EM, we provide the full-length structures of HECTD3 in both apo and ubiquitin-loaded forms, revealing key insights into its domain organisation, including discovery of a distinct fold of the N-terminal region, and mechanistic features. Some of these are shared with other HECT ligases, while others are unique to HECTD3 and contribute to differences in its catalytic mechanisms and functional diversity. Less
Doxorubicin a widely used chemotherapy drug is produced by Streptomyces peucetius ATCC The biosynthesis relies on the cytochrome P monooxygenase DoxA which catalyzes three consecutive late-stage oxidation steps However conversion from daunorubicin to doxorubicin is inefficient necessitating semi-synthetic industrial manufacturing Here we address key limitations in DoxA catalysis We identify the natural redox partners ferredoxin Fdx and ferredoxin reductase FdR by transcriptomic analysis We discovered the vicinal oxygen chelate family protein DnrV to prevent product inhibition by binding doxorubicin Structural analysis of DoxA and density functional theory DFT calculations reveal that inefficient C hydroxylation results from the unfavorable anti-conformation of ... More
Doxorubicin, a widely used chemotherapy drug, is produced by Streptomyces peucetius ATCC27952. The biosynthesis relies on the cytochrome P450 monooxygenase DoxA, which catalyzes three consecutive late-stage oxidation steps. However, conversion from daunorubicin to doxorubicin is inefficient, necessitating semi-synthetic industrial manufacturing. Here, we address key limitations in DoxA catalysis. We identify the natural redox partners ferredoxin Fdx4 and ferredoxin reductase FdR3 by transcriptomic analysis. We discovered the vicinal oxygen chelate family protein DnrV to prevent product inhibition by binding doxorubicin. Structural analysis of DoxA and density functional theory (DFT) calculations reveal that inefficient C14 hydroxylation results from the unfavorable anti-conformation of the methyl ketone side chain of daunorubicin. We harness these advances for rational strain engineering, leading to an 180% increase in doxorubicin yields and an improved production profile. This study provides singular insights into enzymatic constraints in anthracycline biosynthesis and facilitates cost-effective manufacturing to meet the growing global demand for doxorubicin. Less
Natural resistance-associated macrophage proteins Nramps are divalent transition metal transporters found in most organisms typically coupling metal uptake to proton co-transport How this coupling evolved however remains unclear We present structural functional and evolutionary analyses of a clade B Nramp from the gut bacterium Bacteroides fragilis BfraNramp Phylogenetic reconstruction positions clade B as the most basal group of canonical Nramps retaining conserved metal-binding motifs while lacking most residues that form the canonical proton pathway We show that BfraNramp efficiently transports Mn and Cd with high apparent affinity but without proton co-transport or dependence on membrane potential or pH Structures of ... More
Natural resistance-associated macrophage proteins (Nramps) are divalent transition metal transporters found in most organisms, typically coupling metal uptake to proton co-transport. How this coupling evolved, however, remains unclear. We present structural, functional, and evolutionary analyses of a clade B Nramp from the gut bacterium Bacteroides fragilis (BfraNramp). Phylogenetic reconstruction positions clade B as the most basal group of canonical Nramps, retaining conserved metal-binding motifs while lacking most residues that form the canonical proton pathway. We show that BfraNramp efficiently transports Mn²⁺ and Cd²⁺ with high apparent affinity but without proton co-transport or dependence on membrane potential or pH. Structures of metal-free and Mn²⁺-bound BfraNramp reveal an inward-open conformation and a distinct metal coordination geometry involving a conserved glutamate on transmembrane helix 3. Together, these results identify clade B Nramps as proton-independent transition metal uniporters and suggest that proton coupling emerged later in Nramp evolution, following establishment of the metal-binding site. Less
The recent discovery of the isonitrile biosynthetic enzyme ScoE expanded the catalytic repertoire of the Fe II KG-dependent dioxygenase enzyme family ScoE synthesizes an isonitrile functional group from a glycyl-fatty acid adduct with both the isonitrile nitrogen and carbon atoms coming from the glycyl moiety This challenging chemistry cannot be performed in a single step Instead the mechanism appears to require two half reactions each involving KG cleavage to generate a highly reactive iron-oxygen species Here we report sixteen crystal structures that provide snapshots along the reaction trajectory of Rv a ScoE homolog from Mycobacterium tuberculosis These structures which are ... More
The recent discovery of the isonitrile biosynthetic enzyme ScoE expanded the catalytic repertoire of the Fe(II)/αKG-dependent dioxygenase enzyme family. ScoE synthesizes an isonitrile functional group from a glycyl-fatty acid adduct, with both the isonitrile nitrogen and carbon atoms coming from the glycyl moiety. This challenging chemistry cannot be performed in a single step. Instead, the mechanism appears to require two half reactions, each involving αKG cleavage to generate a highly reactive iron-oxygen species. Here, we report sixteen crystal structures that provide snapshots along the reaction trajectory of Rv0097, a ScoE homolog from Mycobacterium tuberculosis. These structures, which are both of wild-type and Rv0097 variants, include a substrate 3-((carboxymethyl)amino)decanoic acid (CADA)-bound structure, an αKG-bound structure, and a structure with both CADA and αKG bound. These structural data reveal how Rv0097 employs conformational rearrangements to protect the unstable CADA-reaction intermediate that is formed in the first half reaction while swapping out αKG cleavage products for a second molecule of αKG. Additionally, these structures, together with data from site-directed mutagenesis, provide insight into Rv0097’s preference for substrates with long alkyl chains, potentially facilitating efforts to re-engineer ScoE/Rv0097 to synthesize isonitrile functional groups on a wider range of small molecules. Less
The ToxRS system is a member of a two-protein transmembrane transcriptional regulator family of proteins that act as critical environmental stress sensors and regulate virulence gene expression in some bacterial pathogens These systems are thought to operate by sensing environmental stimuli and transmitting signals through periplasmic domains to activate DNA-binding transcription factors In Vibrio parahaemolyticus and Vibrio cholerae the ToxRS system regulates virulence factors responsible for severe gastrointestinal symptoms in humans ToxS has been shown to modulate the activity of its binding partner ToxR by binding bile salts antimicrobial cholesterol metabolites secreted into the human gut However the molecular mechanism ... More
The ToxRS system is a member of a two-protein transmembrane transcriptional regulator family of proteins that act as critical environmental stress sensors and regulate virulence gene expression in some bacterial pathogens. These systems are thought to operate by sensing environmental stimuli and transmitting signals through periplasmic domains to activate DNA-binding transcription factors. In Vibrio parahaemolyticus and Vibrio cholerae, the ToxRS system regulates virulence factors responsible for severe gastrointestinal symptoms in humans. ToxS has been shown to modulate the activity of its binding partner ToxR by binding bile salts, antimicrobial cholesterol metabolites secreted into the human gut. However, the molecular mechanism underlying this regulation is unclear. Here, we present the crystal structures of the V. parahaemolyticus ToxS periplasmic domain (ToxSp) with and without the bile salt glycocholate. ToxSp forms an 8-stranded broken β-barrel with a central α-helix and is structurally homologous to a group of chaperone proteins. Notably, the glycocholate-bound ToxSp structure forms a strand-swapped homodimer containing three bound glycocholate molecules. Modeling two ToxR periplasmic domains in complex with the glycocholate-bound ToxSp dimer provides a structure-based model for bile salt activation of the ToxRS system and suggests that ToxRS homologs may be regulated in a similar manner across diverse bacterial species. Less
Iron homeostasis in various pathogenic bacteria is regulated by bacterioferritins Bfr which function to store Fe and release Fe as needed for metabolic processes The Bfr structure consists of kDa subunits in which dimer pairs bind a heme molecule and are assembled into a highly symmetrical -meric spherical structure with an internal core diameter of approximately Release of iron is facilitated by the binding of a kDa Fe- S ferredoxin Bfd to specific sites on the surface of Bfr which transfers electrons to the core thereby reducing the stored Fe to Fe for mobilization The crystal structures of Bfr from ... More
Iron homeostasis in various pathogenic bacteria is regulated by bacterioferritins (Bfr) which function to store Fe3+ and release Fe2+ as needed for metabolic processes. The Bfr structure consists of 18 kDa subunits in which dimer pairs bind a heme molecule and are assembled into a highly symmetrical 24-meric spherical structure with an internal core diameter of approximately 80 Å. Release of iron is facilitated by the binding of a 7 kDa [2Fe-2S] ferredoxin (Bfd) to specific sites on the surface of Bfr which transfers electrons to the core thereby reducing the stored Fe3+ to Fe2+ for mobilization. The crystal structures of Bfr from Brucella abortus (Ba) in the apo and iron bound forms are presented and compared with those from Acinetobacter baumannii (Ab) and Pseudomonas aeruginosa (Pa). Additionally, models of the Bfr:Bfd complexes for Ba and Ab are provided and compared with the Pa complex. Finally, compounds known to target the Bfr:Bfd interaction in Pa were docked to the Ba and Ab structures which provided insight regarding the potential binding mode and inhibitory mechanism. Less
UreE is a nickel chaperone required for the safe and efficient delivery of nickel to the active site of the metalloenzyme urease a key virulence factor of the urinary tract pathogen Proteus mirabilis We investigated the structural features of P mirabilis UreE using protein X-ray crystallography and its nickel-binding capacity by inductively coupled plasma-mass spectrometry Here we report a crystal structure of homodimeric PmUreE and show it has capacity to bind five nickel ions per dimer Truncation of the histidine-rich C-terminus reduced nickel binding capacity by two nickel ions per dimer and comparison with homologous UreE structures allowed the assignment ... More
UreE is a nickel chaperone required for the safe and efficient delivery of nickel to the active site of the metalloenzyme, urease; a key virulence factor of the urinary tract pathogen, Proteus mirabilis. We investigated the structural features of P. mirabilis UreE using protein X-ray crystallography and its nickel-binding capacity by inductively coupled plasma-mass spectrometry. Here, we report a 2.0 Å crystal structure of homodimeric PmUreE and show it has capacity to bind five nickel ions per dimer. Truncation of the histidine-rich C-terminus reduced nickel binding capacity by two nickel ions per dimer and comparison with homologous UreE structures allowed the assignment of putative nickel binding sites within the PmUreE structure. These findings increase our understanding of how PmUreE binds nickel and ultimately prevents this toxic metal from causing significant cellular damage in P. mirabilis. Less
Human T-cell Leukemia Virus type HTLV- is an untreatable retrovirus that causes lethal malignancies and degenerative inflammatory conditions Effective treatments have been delayed by substantial gaps in our knowledge of the fundamental virology especially when compared to the closely related virus HIV A recently developed and highly effective anti-HIV strategy is to target the virus with drugs that interfere with capsid integrity and interactions with the host Importantly the first in class anti-capsid drug approved lenacapavir can provide long-acting pre-exposure prophylaxis Such a property would provide a means to prevent the transmission of HTLV- but its capsid has not previously ... More
Human T-cell Leukemia Virus type 1 (HTLV-1) is an untreatable retrovirus that causes lethal malignancies and degenerative inflammatory conditions. Effective treatments have been delayed by substantial gaps in our knowledge of the fundamental virology, especially when compared to the closely related virus, HIV. A recently developed and highly effective anti-HIV strategy is to target the virus with drugs that interfere with capsid integrity and interactions with the host. Importantly, the first in class anti-capsid drug approved, lenacapavir, can provide long-acting pre-exposure prophylaxis. Such a property would provide a means to prevent the transmission of HTLV-1, but its capsid has not previously been considered as a drug target. Here we describe the first high-resolution crystal structures of the HTLV-1 capsid protein, define essential lattice interfaces, and identify a previously unknown ligand-binding pocket. We show that this pocket is essential for virus infectivity, providing a potential target for future anti-capsid drug development. Less
Photobleaching of fluorescent proteins often limits the acquisition of high-quality images in microscopy StayGold a novel dimeric GFP recently monomerized through sequence engineering addresses this challenge with its high photostability There is now a focus on producing different colored StayGold derivatives to facilitate concurrent tagging of multiple targets The unnatural amino acid -aminotyrosine has previously been shown to redshift superfolder GFP upon incorporation into its chromophore via genetic code expansion Here we apply the same strategy to redshift StayGold through substitution of tyrosine- with -aminotyrosine The resultant red fluorescent protein StayRose shows an excitation wavelength maximum of nm and an ... More
Photobleaching of fluorescent proteins often limits the acquisition of high-quality images in microscopy. StayGold, a novel dimeric GFP recently monomerized through sequence engineering, addresses this challenge with its high photostability. There is now a focus on producing different colored StayGold derivatives to facilitate concurrent tagging of multiple targets. The unnatural amino acid 3-aminotyrosine has previously been shown to redshift superfolder GFP upon incorporation into its chromophore via genetic code expansion. Here, we apply the same strategy to redshift StayGold through substitution of tyrosine-58 with 3-aminotyrosine. The resultant red fluorescent protein, StayRose, shows an excitation wavelength maximum of 530 nm and an emission wavelength maximum of 588 nm. Importantly, the monomeric mStayRose retains the favorable photostability in vivo in Escherichia coli and zebrafish embryos. A high-resolution crystal structure of StayRose confirms the modified structure of the amino chromophore within an unperturbed 3D fold. Although reliant on genetic code expansion, StayRose provides an important step toward developing redshifted StayGold derivatives. Less
Heliorhodopsins HeRs the third rhodopsin family are characterized by inverted membrane topology and confinement to monoderm organisms yet their biological meaning has so far remained a mystery We report the first crystal structure of a eukaryotic HeR supported by structural modeling and comparative analyses across all domains of life A conserved carotenoid-binding site reminiscent of secondary antennae in some microbial rhodopsins is identified and found to be common among HeRs We show that inverted topology allows recruitment of exogenous xanthophylls inaccessible in diderm cells explaining HeRs distinctive orientation and distribution These findings reveal a previously unrecognized light-harvesting mechanism of HeRs ... More
Heliorhodopsins (HeRs), the third rhodopsin family, are characterized by inverted membrane topology and confinement to monoderm organisms, yet their biological meaning has so far remained a mystery. We report the first crystal structure of a eukaryotic HeR, supported by structural modeling and comparative analyses across all domains of life. A conserved carotenoid-binding site, reminiscent of secondary antennae in some microbial rhodopsins, is identified and found to be common among HeRs. We show that inverted topology allows recruitment of exogenous xanthophylls, inaccessible in diderm cells, explaining HeRs’ distinctive orientation and distribution. These findings reveal a previously unrecognized light-harvesting mechanism of HeRs, expand the known repertoire of microbial phototrophy, and suggest evolutionary constraints linking membrane topology to environmental metabolite accessibility. Less
The composition of the primordial genetic material remains uncertain Studies of duplex structure and stability and of nonenzymatic template copying chemistry provide insight into the viability of potentially primordial genetic polymers Recent work suggests that - deoxyribo-purine nucleotides may have been generated together with ribonucleotides on the early Earth Since DNA RNA duplexes are known to be less stable than RNA RNA duplexes we have examined the impact of dA dI and dG substitutions on RNA structure and nonenzymatic template copying We find that single -deoxyribo-purine substitutions reduce RNA duplex stability as expected Crystallographic studies show that such substitutions lead ... More
The composition of the primordial genetic material remains uncertain. Studies of duplex structure and stability, and of nonenzymatic template copying chemistry, provide insight into the viability of potentially primordial genetic polymers. Recent work suggests that 2′- deoxyribo-purine nucleotides may have been generated together with ribonucleotides on the early Earth. Since DNA/RNA duplexes are known to be less stable than RNA/RNA duplexes, we have examined the impact of dA, dI, and dG substitutions on RNA structure and nonenzymatic template copying. We find that single 2′-deoxyribo-purine substitutions reduce RNA duplex stability, as expected. Crystallographic studies show that such substitutions lead to minimal structural changes but point to diminished solvation as a likely reason for duplex destabilization. Kinetic studies show that dI and dG substrates exhibit slightly weaker template binding and slower rates of template-directed primer extension than the corresponding ribo-purine substrates. In contrast, dA substrates exhibit much slower reaction kinetics but higher template affinity than rA substrates. Our results suggest that a mixed RNA/DNA primordial genetic polymer would have suffered from moderately slower rates of template copying, but that this could have been offset by an advantage due to more facile strand separation or exchange. Less
C domains are ubiquitous membrane-binding modules of residues in eukaryotes that are often associated with proteins involved in membrane trafficking and lipid modification The genome of Trichomonas vaginalis the most common non-viral sexually transmitted human pathogen encodes eight genes that contain a N-terminal C module linked to a XYPPX-repeat domain of more than four XYPPX repeats C -XYPPX While the function of the XYPPX-repeat domain remains unknown its multiple association with C domains in T vaginalis suggests it is important The C domain from one of these C -XYPPX-repeat proteins Tv-C - was structurally and physically characterized using X-ray crystallography ... More
C2 domains are ubiquitous membrane-binding modules of ∼130 residues in eukaryotes that are often associated with proteins involved in membrane trafficking and lipid modification. The genome of Trichomonas vaginalis, the most common, non-viral, sexually transmitted human pathogen, encodes eight genes that contain a N-terminal C2 module linked to a XYPPX-repeat domain of more than four XYPPX repeats (C2-XYPPX). While the function of the XYPPX-repeat domain remains unknown, its multiple association with C2 domains in T. vaginalis suggests it is important. The C2 domain from one of these C2-XYPPX-repeat proteins, Tv-C2-1, was structurally and physically characterized using X-ray crystallography and NMR spectroscopy. The crystal structure for Tv-C2-1 shows that this domain shares a fold common to all C2 domains, a compact Greek-key motif composed of eight anti-parallel β-strands in the type-2 topology. An NMR chemical shift perturbation study with Ca2+ showed that Tv-C2-1 bound two Ca2+ atoms primarily via two loops (loop-1 and loop-3) on the predicted calcium binding face of the protein with Kds of 58.0 ± 0.1 μM and 232 ± 6 μM. Estimations of the overall rotational correlation time, τc, in the apo (11.1 ns) and Ca2+-bound (9.2 ns) state suggests the protein becomes more compact upon Ca2+ binding, consistent with a decrease in dynamics in loop-3 and marginally in loop-1 suggested by amide 15N heteronuclear steady-state {1H}-15N NOEs. Showing Tv-C2-1 binds calcium and adopts a compact Greek-key motif structure, two primary features of C2 domains, suggests understanding the function of the XYPPX-repeat domain may be warranted. Less
Severe acute respiratory syndrome coronavirus SARS-CoV- continues to threaten global health This underpins the need for novel therapeutics against this virus Nonstructural protein Nsp of SARS-CoV- is a multifunctional protein with an essential role in viral replication As such it presents itself as an attractive target for drug discovery Here we describe two crystallographic fragment-screening campaigns against Nsp one using the established F X-Entry Screen and one using a new chemically and structurally diverse fragment library which we call the KIT library Together hits could be identified from screened fragments which constitutes the highest hit rate reported for Nsp to ... More
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to threaten global health. This underpins the need for novel therapeutics against this virus. Nonstructural protein 1 (Nsp1) of SARS-CoV-2 is a multifunctional protein with an essential role in viral replication. As such, it presents itself as an attractive target for drug discovery. Here, we describe two crystallographic fragment-screening campaigns against Nsp1, one using the established F2X-Entry Screen and one using a new, chemically and structurally diverse fragment library, which we call the KIT library. Together, 21 hits could be identified from 192 screened fragments, which constitutes the highest hit rate reported for Nsp1 to date. Many hits bind to a key functional region and interact with residues involved in cellular mRNA cleavage, ribosome binding and viral RNA recognition. Furthermore, most of the identified fragments share a common binding mode, providing promising starting points for further optimization into drug-like compounds that can disrupt the role of Nsp1 in viral replication. Less
Ferritins are a widespread family of proteins involved in iron homeostasis While classic ferritins consist of four -helices and form -meric nanocages related ferritin-like proteins display other types of assemblies and sometimes lack any iron storage capacity Here by analyzing the available genomic data we identify a family of double ferritin-like proteins DFLPs composed of two four-helical domains which arose by duplication of a ferritin fold protein We characterize representative DFLPs from Thermocrinis minervae and Caldanaerovirga acetigignens TmDFLP and CaDFLP and show that they form homodimers and bind heme We determine the X-ray structure of TmDFLP and demonstrate its ferroxidase ... More
Ferritins are a widespread family of proteins involved in iron homeostasis. While classic ferritins consist of four α-helices and form 24-meric nanocages, related ferritin-like proteins display other types of assemblies and sometimes lack any iron storage capacity. Here, by analyzing the available genomic data, we identify a family of double ferritin-like proteins (DFLPs) composed of two four-helical domains, which arose by duplication of a ferritin fold protein. We characterize representative DFLPs from Thermocrinis minervae and Caldanaerovirga acetigignens, TmDFLP and CaDFLP, and show that they form homodimers and bind heme. We determine the X-ray structure of TmDFLP and demonstrate its ferroxidase activity. Furthermore, we show that some DFLPs, including TmDFLP and CaDFLP, are highly likely to be targeted into encapsulin shells. Our work expands the range of known iron metabolism systems and highlights the power of genome mining for discovery of new proteins. Less
In more and more drug discovery projects crystallographic fragment screening CFS is employed as an early screening method Here we demonstrate that choosing the right crystal form has a profound influence on the hit rates and hence success and speed of downstream lead generation Two CFS campaigns with the same fragment library and an almost identical experimental setup were carried out against the two crystal forms of the SARS-CoV- main protease While both crystal forms exhibit similar diffraction properties the observed hit rates in the two campaigns were vastly different For the monoclinic crystals a hit rate of was determined ... More
In more and more drug discovery projects, crystallographic fragment screening (CFS) is employed as an early screening method. Here, we demonstrate that choosing the right crystal form has a profound influence on the hit rates and hence success and speed of downstream lead generation. Two CFS campaigns with the same fragment library and an almost identical experimental setup were carried out against the two crystal forms of the SARS-CoV-2 main protease.While both crystal forms exhibit similar diffraction properties, the observed hit rates in the two campaigns were vastly different. For the monoclinic crystals a hit rate of 3% was determined, while a hit rate of 16% was observed for the orthorhombic crystals. These findings align with the more open molecular packing in the orthorhombic crystals where the solvent channels leading to the active sites are about twice larger than in the monoclinic crystal form. Our results highlight the critical importance of the crystal system in a crystallographic fragment-screening campaign and identify this parameter as one of the most important ones to be optimized during preparation of a campaign. Less
Glutarimide analogs such as thalidomide redirect the E ubiquitin ligase CRL CRBN to induce degradation of certain zinc finger ZF proteins Although the core structural motif recognized by CRBN has been characterized it does not fully explain substrate specificity To explore the role of residues adjacent to this core motif we constructed a comprehensive ZF reporter library of reporters derived from human ZF proteins and conducted a library-on-library screen with glutarimide analogs to identify compounds that collectively degrade ZF reporters Cryo-electron microscopy and crystal structures of ZFs in complex with CRBN revealed the importance of interactions beyond the core ZF ... More
Glutarimide analogs, such as thalidomide, redirect the E3 ubiquitin ligase CRL4CRBN to induce degradation of certain zinc finger (ZF) proteins. Although the core structural motif recognized by CRBN has been characterized, it does not fully explain substrate specificity. To explore the role of residues adjacent to this core motif, we constructed a comprehensive ZF reporter library of 9,097 reporters derived from 1,655 human ZF proteins and conducted a library-on-library screen with 29 glutarimide analogs to identify compounds that collectively degrade 38 ZF reporters. Cryo-electron microscopy and crystal structures of ZFs in complex with CRBN revealed the importance of interactions beyond the core ZF degron. We used systematic mutagenesis of ZFs and CRBN to identify modes of neosubstrate recruitment requiring distinct amino acids. Finally, we found subtle chemical variations in glutarimide analogs that alter target scope and selectivity, thus providing a roadmap for their rational design. Less
Transcription factors TFs regulate gene expression by engaging chromatin remodeling complexes yet the structural principles governing these critical interactions remain poorly defined Here we uncover the molecular mechanism by which lineage-specific pioneer transcription factor PU encoded by SPI directly engages the BAF mSWI SNF chromatin remodeling complex First using a variety of genomic approaches we establish that BAF collaborates with PU to regulate transcription in AML cells Then using a combination of biochemistry and biophysics mass spectrometry-based protein footprinting and crystallography we map the PU -BAF A interface to a disordered region of PU that adopts a helical conformation upon ... More
Transcription factors (TFs) regulate gene expression by engaging chromatin remodeling complexes, yet the structural principles governing these critical interactions remain poorly defined. Here, we uncover the molecular mechanism by which lineage-specific pioneer transcription factor PU.1 (encoded by SPI1) directly engages the BAF (mSWI/SNF) chromatin remodeling complex. First, using a variety of genomic approaches, we establish that BAF collaborates with PU.1 to regulate transcription in AML cells. Then, using a combination of biochemistry and biophysics, mass spectrometry-based protein footprinting, and crystallography, we map the PU.1-BAF60A interface to a disordered region of PU.1 that adopts a helical conformation upon binding to the YEATS-like domain of BAF60A. Disruption of this functionally critical interface via knockdown abrogates the ability of PU.1 to rescue cell viability. Finally, we conducted a high-throughput screen that yielded small molecules which selectively bind BAF60A and disrupt PU.1 binding. Co-crystal structures reveal distinct compound binding modes that converge on a critical PU.1-BAF60A interaction hotspot. These findings define, for the first time, the structural interface between a pioneer transcription factor and the BAF complex and establish a platform that enables targeting transcription factor-chromatin remodeling complex interactions in cancer. Less
Dual-specificity mitogen-activated protein kinase MAPK phosphatases MKPs directly dephosphorylate and inactivate the MAPKs Although the catalytic mechanism of dephosphorylation of the MAPKs by the MKPs is established a complete molecular picture of the regulatory interplay between the MAPKs and MKPs still remains to be fully explored Here we sought to define the molecular mechanism of MKP regulation through an allosteric site within its catalytic domain We demonstrate using crystallographic and NMR spectroscopy approaches that residue Y is required to maintain the structural integrity of the allosteric pocket Along with molecular dynamics simulations these data provide insight into how changes in ... More
Dual-specificity mitogen-activated protein kinase (MAPK) phosphatases (MKPs) directly dephosphorylate and inactivate the MAPKs. Although the catalytic mechanism of dephosphorylation of the MAPKs by the MKPs is established, a complete molecular picture of the regulatory interplay between the MAPKs and MKPs still remains to be fully explored. Here, we sought to define the molecular mechanism of MKP5 regulation through an allosteric site within its catalytic domain. We demonstrate using crystallographic and NMR spectroscopy approaches that residue Y435 is required to maintain the structural integrity of the allosteric pocket. Along with molecular dynamics simulations, these data provide insight into how changes in the allosteric pocket propagate conformational flexibility in the surrounding loops to reorganize catalytically crucial residues in the active site. Furthermore, Y435 contributes to the interaction with p38 MAPK and JNK, thereby promoting dephosphorylation. Collectively, these results highlight the role of Y435 in the allosteric site as a novel mode of MKP5 regulation by p38 MAPK and JNK Less
Transport and Golgi Organization Homolog TANGO protein deficiency disorder TDD is a rare autosomal recessive disorder characterized by multi-systemic abnormalities and significant phenotypic variability including neurodevelopmental delay seizures intermittent ataxia hypothyroidism rhabdomyolysis life-threatening metabolic derangements and cardiac arrhythmias Mutations in TANGO result in mitochondrial dysfunction abnormal lipid homeostasis with cardiolipin deficiency and impaired Golgi-ER trafficking in TANGO patient-derived cells Despite the wide recognition of the clinical manifestations of TDD and numerous molecular studies the precise function of TANGO and the pathophysiology of TDD remain poorly understood A computationally derived three-dimensional structure model suggested that TANGO adopts an -fold similar to ... More
Transport and Golgi Organization 2 Homolog (TANGO2) protein deficiency disorder (TDD) is a rare autosomal recessive disorder characterized by multi-systemic abnormalities and significant phenotypic variability including neurodevelopmental delay, seizures, intermittent ataxia, hypothyroidism, rhabdomyolysis, life-threatening metabolic derangements, and cardiac arrhythmias. Mutations in TANGO2 result in mitochondrial dysfunction, abnormal lipid homeostasis with cardiolipin deficiency, and impaired Golgi-ER trafficking in TANGO2 patient-derived cells. Despite the wide recognition of the clinical manifestations of TDD and numerous molecular studies, the precise function of TANGO2 and the pathophysiology of TDD remain poorly understood. A computationally derived three-dimensional structure model suggested that TANGO2 adopts an αββα-fold, similar to the N-terminal nucleophile aminohydrolase (Ntn) superfamily of proteins, but the experimentally verified structure has not been available thus far. Here, we present the first crystal structure of the recombinant human TANGO2, determined at 1.70 Å resolution. The X-ray structure data confirmed its predicted tertiary fold with similarity to the Ntn-hydrolase family of proteins, and the comparative analysis of the active site architecture, including residues involved in catalysis and putative ligand binding site, suggests a potential hydrolase function. Additional examination of the common mutation sites found in TDD patients provides insight regarding their potential effect on protein structure integrity. Less
Malaria poses an enormous threat to human health With ever-increasing resistance to currently deployed antimalarials new targets and starting point compounds with novel mechanisms of action need to be identified Here we explore the antimalarial activity of the Streptomyces sp natural product -O-sulfamoyl- -chloroadenosine dealanylascamycin DACM and compare it with the synthetic adenosine monophosphate AMP mimic -O-sulfamoyladenosine AMS These nucleoside sulfamates exhibit potent inhibition of P falciparum growth with an efficacy comparable to that of the current front-line antimalarial dihydroartemisinin Exposure of P falciparum to DACM leads to inhibition of protein translation driven by eIF phosphorylation We show that DACM ... More
Malaria poses an enormous threat to human health. With ever-increasing resistance to currently deployed antimalarials, new targets and starting point compounds with novel mechanisms of action need to be identified. Here, we explore the antimalarial activity of the Streptomyces sp natural product, 5ʹ-O-sulfamoyl-2-chloroadenosine (dealanylascamycin, DACM) and compare it with the synthetic adenosine monophosphate (AMP) mimic, 5-O-sulfamoyladenosine (AMS). These nucleoside sulfamates exhibit potent inhibition of P. falciparum growth with an efficacy comparable to that of the current front-line antimalarial dihydroartemisinin. Exposure of P. falciparum to DACM leads to inhibition of protein translation, driven by eIF2α phosphorylation. We show that DACM targets multiple amino acyl tRNA synthetase (aaRS) targets, including the cytoplasmic aspartyl tRNA synthetase (AspRS). The mechanism involves hijacking of the reaction product, leading to the formation of a tightly bound inhibitory amino acid-sulfamate conjugate. We show that recombinant P. falciparum and P. vivax AspRS are susceptible to hijacking by DACM and AMS, generating Asp-DACM and Asp-AMS adducts that stabilize these proteins. By contrast, human AspRS appears less susceptible to hijacking. X-ray crystallography reveals that apo P. vivax AspRS exhibits a stabilized flipping loop over the active site that is poised to bind substrates. By contrast, human AspRS exhibits disorder in an extended region around the flexible flipping loop as well as in a loop in motif II. These structural differences may underpin the decreased susceptibility of human AspRS to reaction-hijacking by DACM and AMS. Our work reveals Plasmodium AspRS as a promising antimalarial target and highlights structural features that underpin differences in the susceptibility of aaRSs to reaction hijacking inhibition. Less
Glaucoma is a neurodegenerative condition involving optic nerve damage and retinal ganglion cells death Animal studies suggested that the pathway linking these events can be mediated by mobile zinc secreted into the intraretinal space and exerting cytotoxic effects Whether this mechanism is relevant for human glaucoma and what are the targets of extracellular zinc is unknown We report that increased zinc content in the aqueous humor and retina is indeed a characteristic of glaucomatous neuropathy and excess extracellular zinc may be recognized by the key retinal neurotrophic factor PEDF Biophysical and X-ray crystallographic studies show that PEDF coordinates zinc ions ... More
Glaucoma is a neurodegenerative condition involving optic nerve damage and retinal ganglion cells death. Animal studies suggested that the pathway linking these events can be mediated by mobile zinc secreted into the intraretinal space and exerting cytotoxic effects. Whether this mechanism is relevant for human glaucoma and what are the targets of extracellular zinc is unknown. We report that increased zinc content in the aqueous humor and retina is indeed a characteristic of glaucomatous neuropathy, and excess extracellular zinc may be recognized by the key retinal neurotrophic factor PEDF. Biophysical and X-ray crystallographic studies show that PEDF coordinates zinc ions in five types of intermolecular high-affinity sites, leading to a decrease in negative surface charge and reversible oligomerization of the protein, thereby masking the target recognition sites responsible for its neurotrophic and antiangiogenic activities and collagen binding. Notably, PEDF secretion is enhanced in both glaucoma and retinal cell models in response to zinc stress; however, zinc binding negatively affects axogenic, differentiative and prosurvival functions of PEDF by suppressing its ability to activate receptor PEDF-R/PNPLA2. We suggest that glaucomatous neurodegeneration is associated with direct inhibition of PEDF signaling by extracellular zinc, making their complex a promising target for neuroprotective therapy. Less
Glycyl tRNA synthetases GlyRSs are prospective drug targets for combating Mycobacterium tuberculosis Mtb and cancer in humans These synthetases are of the -subtype with the ortholog in humans being dual targeted to the cytosol and mitochondria Whereas the human enzyme has been structurally characterized previously in several liganded states no structures of MtbGlyRS have thus far been reported Here we describe our recent work with MtbGlyRS and the closely-related Mycobacterium thermoresitibile GlyRS MtrGlyRS which progressed through all phases of the structural genomics pipeline for the purpose of facilitating structure-based drug discovery MtbGlyRS was expressed in Mycobacterium smegmatis and MtrGlyRS in ... More
Glycyl tRNA synthetases (GlyRSs) are prospective drug targets for combating Mycobacterium tuberculosis (Mtb) and cancer in humans. These synthetases are of the α2-subtype, with the ortholog in humans being dual targeted to the cytosol and mitochondria. Whereas the human enzyme has been structurally characterized previously in several liganded states, no structures of MtbGlyRS have thus far been reported. Here, we describe our recent work with MtbGlyRS and the closely-related Mycobacterium thermoresitibile GlyRS (MtrGlyRS), which progressed through all phases of the structural genomics pipeline, for the purpose of facilitating structure-based drug discovery. MtbGlyRS was expressed in Mycobacterium smegmatis and MtrGlyRS in Escherichia coli. Crystal structures are described for complexes of the two enzymes with adenosine monophosphate (AMP) and glycyl-sulfamoyl-adenylate (glycyl-AMS) at resolutions of 1.65/2.90 and 2.25/1.95 Å, respectively, and for MtrGlyRS in its apo state at 2.85 Å. Despite crystallizing in the dimeric state characteristic of many class II synthetases, the two enzymes elute predominantly as monomers during size exclusion chromatography. Strikingly, significant portions of the dimer interface and active site are unstructured in the MtrGlyRS apoenzyme crystal. AMP orders two tRNA recognition loops and a section of the insertion domain, and glycyl-AMS further stabilizes the structure, including the closure of a lid motif. Both the active and anticodon binding sites display structural differences with the human GlyRS and thus the collection of crystal structures should be useful for guiding drug development efforts targeting the various characterized structural states. Less
Room-temperature RT X-ray diffraction experiments enable us to investigate protein dynamics efficiently probe fragment binding and perform time-resolved crystallography experiments The Versatile Macromolecular Crystallography in-situ VMXi beamline at Diamond Light Source DLS in the United Kingdom specializes in the collection of RT X-ray diffraction data in situ directly from crystallization trays without any manipulation of protein crystals improving crystal integrity for fragile crystals While many X-ray sources are now equipped to grow crystals on site for in-situ experiments to date there has been no comprehensive analysis that we are aware of on the effect of shipping crystals on plates at ... More
Room-temperature (RT) X-ray diffraction experiments enable us to investigate protein dynamics, efficiently probe fragment binding, and perform time-resolved crystallography experiments. The Versatile Macromolecular Crystallography in-situ (VMXi) beamline at Diamond Light Source (DLS) in the United Kingdom specializes in the collection of RT X-ray diffraction data in situ directly from crystallization trays without any manipulation of protein crystals, improving crystal integrity for fragile crystals. While many X-ray sources are now equipped to grow crystals on site for in-situ experiments, to date there has been no comprehensive analysis that we are aware of on the effect of shipping crystals on plates at ambient temperature for RT data collection, while the equivalent methodology for cryo-cooled crystals is well established. Here we examine the impact of shipping on crystals grown on MiTeGen In Situ-1 plates at the University of Buffalo Hauptman Woodward Research Institute (UB-HWI) in Buffalo, NY, United States transatlantic to DLS in Didcot, United Kingdom. We utilized the Stanford Synchrotron Radiation Lightsource (SSRL) Blue Box Thermal Shipper (Blue Box), which can maintain temperature for up to 168 hours, to ship crystallization plates at room temperature from UB-HWI to DLS. We hypothesized that long-distance shipping might compromise data quality through mechanical stress or temperature fluctuations. Instead, we found that room-temperature data collected at VMXi showed no significant differences for crystals set up at UB-HWI and shipped relative to crystals set up on site in the UK. High-resolution structures were successfully determined for all proteins in the study, demonstrating that long-distance shipment of crystals at non-cryogenic temperatures is feasible without compromising diffraction quality. This study provides a proof-of-concept workflow for expanding access to room-temperature crystallography worldwide, enabling more researchers to leverage cutting-edge techniques without needing to grow crystals on site. Less
In this work we present the high-resolution structure of human aconitate decarboxylase hACOD in its true apo form active site empty as well in complex with the inhibitor citraconate These two new structures show the architecture of the active site and the structure-activity relationships of citraconate inhibition Careful analysis of the structures indicates probable dynamics required for substrate inhibitor binding and catalysis These observations were further explored using molecular dynamic simulations which show a clear open-close mechanism of hACOD between the A and A loops the lid- and helical-domain respectively As part of the biochemical characterization of the protein we ... More
In this work, we present the high-resolution structure of human aconitate decarboxylase 1 (hACOD1) in its true apo form (active site empty) as well in complex with the inhibitor citraconate. These two new structures show the architecture of the active site and the structure-activity relationships of citraconate inhibition. Careful analysis of the structures indicates probable dynamics required for substrate/inhibitor binding and catalysis. These observations were further explored using molecular dynamic simulations, which show a clear open-close mechanism of hACOD1 between the A1 and A2 loops, the lid- and helical-domain respectively. As part of the biochemical characterization of the protein, we also developed an alternative kinetic assay which measures the rate of catalysis of hACOD1 by direct observation of the conversion of cis-aconitate to itaconate by NMR spectroscopy. The work herein offers a foundation for structure- and dynamic-driven design of novel hACOD1 inhibitors as novel chemotherapeutics. Less
Flavin-binding proteins flavoproteins are widespread in nature revealing versatile oxidation-reduction reactions and photochemistry Flavoproteins derived from LOV domains are used for engineering of ligh-tresponsive tools in optogenetics as well as fluorescent markers and photogenerators of reactive oxygen species Despite extensiev efforts all currently used LOV-derived proteins have similar absorption spectra with maxima around - and - nm Here we describe the discovery of a large Stokes shift flavi-nbased fluorescent protein LSSFbFP which can be obtainedin vivo and in vitro with absorption maxima at - and - nm Fluorescence emission of LSSFbFP mirrors that of classical FbFPs with the maximum at ... More
Flavin-binding proteins (flavoproteins) are widespread in nature, revealing versatile oxidation-reduction reactions and photochemistry. Flavoproteins derived from LOV domains are used for engineering of ligh-tresponsive tools in optogenetics, as well as fluorescent markers and photogenerators of reactive oxygen species. Despite extensiev efforts, all currently used LOV-derived proteins have similar absorption spectra with maxima around 275, 35-0375, and 450-485 nm. Here, we describe the discovery of a large Stokes shift flavi-nbased fluorescent protein, LSSFbFP, which can be obtainedin vivo and in vitro, with absorption maxima at 340-350 and 395-405 nm. Fluorescence emission of LSSFbFP mirrors that of classical FbFPs with the maximum at ~500 nm. We sho that the protein binds lumichrome as the chromophore and use low temperature and time-resolved spectroscopy, X-ray crystallography and modeling to prove that the apparent Stokes shift of LSSFbFP occurs due to excited state proton phenomena observed in flavoproteni s and pave the way for engineering of new flavin-based molecular instruments. Less
In the human commensal Gram-positive bacterial pathogen Streptococcus pneumoniae the essential extracellular cell-division-associated peptidoglycan PG hydrolase PcsB interacts directly with the cytoplasmic-membrane-bound complex between FtsE and FtsX PcsB contains a cysteine hishdine-dependent amidohydrolase pephdase CHAP domain responsible for PG hydrolysis as well as a coiled-coil domain required for interaction with FtsEX ATP hydrolysis of FtsE in the cytoplasm drives conformational changes in FtsX in the cytoplasmic membrane which ultimately regulates the PG hydrolase on the outside of the cell In this work we show using in vitro and in vivo approaches that the CHAP domain of PcsB predominately functions as ... More
In the human commensal Gram-positive bacterial pathogen Streptococcus pneumoniae, the essential extracellular cell-division-associated peptidoglycan (PG) hydrolase PcsB interacts directly with the cytoplasmic-membrane-bound complex between FtsE and FtsX (1–3). PcsB contains a cysteine, hishdine-dependent amidohydrolase/pephdase (CHAP) domain responsible for PG hydrolysis, as well as a coiled-coil domain required for interaction with FtsEX (1,4). ATP hydrolysis of FtsE in the cytoplasm drives conformational changes in FtsX in the cytoplasmic membrane, which ultimately regulates the PG hydrolase on the outside of the cell (5). In this work we show using in vitro and in vivo approaches, that the CHAP domain of PcsB predominately functions as an iso-D-Glutaminyl-Lysyl D,L-endopeptidase, with particular substrate specificity for Lys-containing, amidated PG, cleaving between the second and third amino acids of the peptidoglycan stem peptide. The catalytic activity of PcsB is regulated and activated by conformation changes of the coiled-coil region of PcsB and in part by a short helical region immediately adjacent to the CHAP domain to guard against PcsB hydrolytic activation outside of its cell division specific functional requirement. This work supports a model for the overall biological activity of the FtsEX-PcsB complex, in which ATP hydrolysis by FtsE in the cytoplasm, drives conformational changes in FtsX and PcsB resulting in the liberation of the hydrolytic CHAP domain of PcsB from its regulatory helix to allow PG stem peptide cleavage that splits the septal disk and marks a region of the peptidoglycan sacculus for subsequent cell division remodelling. Less
Nonenzymatic RNA copying is thought to have been responsible for the replication of genetic information during the origin of life However chemical copying with the canonical nucleotides A U G and C strongly favors the incorporation of G and C and disfavors the incorporation of A and especially U because of the stronger G C vs A U base pair and the weaker stacking interactions of U Recent advances in prebiotic chemistry suggest that the -thiopyrimidines were precursors to the canonical pyrimidines raising the possibility that they may have played an important early role in RNA copying chemistry Furthermore -thiouridine ... More
Nonenzymatic RNA copying is thought to have been responsible for the replication of genetic information during the origin of life. However, chemical copying with the canonical nucleotides (A, U, G, and C) strongly favors the incorporation of G and C and disfavors the incorporation of A and especially U, because of the stronger G:C vs. A:U base pair, and the weaker stacking interactions of U. Recent advances in prebiotic chemistry suggest that the 2-thiopyrimidines were precursors to the canonical pyrimidines, raising the possibility that they may have played an important early role in RNA copying chemistry. Furthermore, 2-thiouridine (s2U) and inosine (I) form by deamination of 2-thiocytidine (s2C) and A respectively. We used thermodynamic and crystallographic analyses to compare the I:s2C and A:s2U base pairs. We find that the I:s2C base pair is isomorphic and isoenergetic with the A:s2U base pair. The I:s2C base pair is weaker than a canonical G:C base pair, while the A:s2U base pair is stronger than the canonical A:U base pair, so that a genetic alphabet consisting of s2U, s2C, I and A generates RNA duplexes with uniform base pairing energies. Consistent with these results, kinetic analysis of nonenzymatic template-directed primer extension reactions reveals that s2C and s2U substrates bind similarly to I and A in the template, and vice versa. Our work supports the plausibility of a potentially primordial genetic alphabet consisting of s2U, s2C, I and A, and offers a potential solution to the long-standing problem of biased nucleotide incorporation during nonenzymatic template copying. Less