A high-throughput structural system biology approach to increase structure representation of proteins from Clostridioides difficile.

Clostridioides difficile causes life-threatening gastrointestinal infections. It is a high-risk pathogen due to a lack of effective treatments, antimicrobial resistance, and a poorly conserved genomic core. Herein, we report 30 X-ray structures from a structure genomics pipeline spanning 13 years, representing 10.2% of the X-ray structures for this important pathogen.

Structural and biochemical characterisation of Co2+-binding sites on serum albumins and their interplay with fatty acids.

Serum albumin-Co2+ interactions are of clinical importance. They play a role in mediating the physiological effects associated with cobalt toxicity and are central to the albumin cobalt binding (ACB) assay for diagnosis of myocardial ischemia. To further understand these processes, a deeper understanding of albumin-Co2+ interactions is required. Here, we present the first crystallographic structures of human serum albumin (HSA; three structures) and equine serum albumin (ESA; one structure) in complex with Co2+. Amongst a total of sixteen sites bearing a cobalt ion across the structures, two locations were prominent, and they relate to metal-binding sites A and B. Site-directed mutagenesis and isothermal titration calorimetry (ITC) were employed to characterise sites on HSA. The results indicate that His9 and His67 contribute to the primary (putatively corresponding to site B) and secondary Co2+-binding sites (site A), respectively. The presence of additional multiple weak-affinity Co2+ binding sites on HSA was also supported by ITC studies. Furthermore, addition of 5 molar equivalents of the non-esterified fatty acid palmitate (C16:0) reduced the Co2+-binding affinity at both sites A and B. The presence of bound myristate (C14:0) in the HSA crystal structures provided insight into the fatty acid-mediated structural changes that diminish the affinity of the protein toward Co2+. Together, these data provide further support for the idea that ischemia-modified albumin corresponds to albumin with excessive fatty-acid loading. Collectively, our findings provide a comprehensive understanding of the molecular underpinnings governing Co2+ binding to serum albumin.

Organism-specific differences in the binding of ketoprofen to serum albumin.

Serum albumin is a circulatory transport protein that has a highly conserved sequence and structure across mammalian organisms. Its ligand-binding properties are of importance as albumin regulates the pharmacokinetics of many drugs. Due to the high degree of structural conservation between mammalian albumins, nonhuman albumins such as bovine serum albumin or animal models are often used to understand human albumin-drug interactions. Ketoprofen is a popular nonsteroidal anti-inflammatory drug that is transported by albumin. Here, it is revealed that ketoprofen exhibits different binding-site preferences when interacting with human serum albumin compared with other mammalian albumins, despite the conservation of binding sites across species. The reasons for the observed differences were explored, including identifying ketoprofen binding determinants at specific sites and the influence of fatty acids and other ligands on drug binding. The presented results reveal that the drug-binding properties of albumins cannot easily be predicted based only on a complex of albumin from another organism and the conservation of drug sites between species. This work shows that understanding organism-dependent differences is essential for assessing the suitability of particular albumins for structural or biochemical studies.

New ligand-binding sites identified in the crystal structures of ß-lactoglobulin complexes with desipramine.

The homodimeric ß-lactoglobulin belongs to the lipocalin family of proteins that transport a wide range of hydrophobic molecules and can be modified by mutagenesis to develop specificity for novel groups of ligands. In this work, new lactoglobulin variants, FAF (I56F/L39A/M107F) and FAW (I56F/L39A/M107W), were produced and their interactions with the tricyclic drug desipramine (DSM) were studied using X-ray crystallography, calorimetry (ITC) and circular dichroism (CD). The ITC and CD data showed micromolar affinity of the mutants for DSM and interactions according to the classical one-site binding model. However, the crystal structures unambiguously showed that the FAF and FAW dimers are capable of binding DSM not only inside the ß-barrel as expected, but also at the dimer interface and at the entrance to the binding pocket. The presented high-resolution crystal structures therefore provide important evidence of the existence of alternative ligand-binding sites in the ß-lactoglobulin molecule. Analysis of the crystal structures highlighted the importance of shape complementarity for ligand recognition and selectivity. The binding sites identified in the crystal structures of the FAF-DSM and FAW-DSM complexes together with data from the existing literature are used to establish a systematic classification of the ligand-binding sites in the ß-lactoglobulin molecule.

Association of Coding Variants in Hydroxysteroid 17-beta Dehydrogenase 14 (HSD17B14) with Reduced Progression to End Stage Kidney Disease in Type 1 Diabetes.

BACKGROUND: Rare variants in gene coding regions likely have a greater impact on disease-related phenotypes than common variants through disruption of their encoded protein. We searched for rare variants associated with onset of ESKD in individuals with type 1 diabetes at advanced kidney disease stage. METHODS: Gene-based exome array analyses of 15,449 genes in five large incidence cohorts of individuals with type 1 diabetes and proteinuria were analyzed for survival time to ESKD, testing the top gene in a sixth cohort (n=2372/1115 events all cohorts) and replicating in two retrospective case-control studies (n=1072 cases, 752 controls). Deep resequencing of the top associated gene in five cohorts confirmed the findings. We performed immunohistochemistry and gene expression experiments in human control and diseased cells, and in mouse ischemia reperfusion and aristolochic acid nephropathy models. RESULTS: Protein coding variants in the hydroxysteroid 17-ß dehydrogenase 14 gene (HSD17B14), predicted to affect protein structure, had a net protective effect against development of ESKD at exome-wide significance (n=4196; P value=3.3 × 10-7). The HSD17B14 gene and encoded enzyme were robustly expressed in healthy human kidney, maximally in proximal tubular cells. Paradoxically, gene and protein expression were attenuated in human diabetic proximal tubules and in mouse kidney injury models. Expressed HSD17B14 gene and protein levels remained low without recovery after 21 days in a murine ischemic reperfusion injury model. Decreased gene expression was found in other CKD-associated renal pathologies. CONCLUSIONS: HSD17B14 gene is mechanistically involved in diabetic kidney disease. The encoded sex steroid enzyme is a druggable target, potentially opening a new avenue for therapeutic development.

Rapid response to emerging biomedical challenges and threats.

As part of the global mobilization to combat the present pandemic, almost 100 000 COVID-19-related papers have been published and nearly a thousand models of macromolecules encoded by SARS-CoV-2 have been deposited in the Protein Data Bank within less than a year. The avalanche of new structural data has given rise to multiple resources dedicated to assessing the correctness and quality of structural data and models. Here, an approach to evaluate the massive amounts of such data using the resource https://covid19.bioreproducibility.org is described, which offers a template that could be used in large-scale initiatives undertaken in response to future biomedical crises. Broader use of the described methodology could considerably curtail information noise and significantly improve the reproducibility of biomedical research.

Crystallographic models of SARS-CoV-2 3CLpro: in-depth assessment of structure quality and validation.

The appearance at the end of 2019 of the new SARS-CoV-2 coronavirus led to an unprecedented response by the structural biology community, resulting in the rapid determination of many hundreds of structures of proteins encoded by the virus. As part of an effort to analyze and, if necessary, remediate these structures as deposited in the Protein Data Bank (PDB), this work presents a detailed analysis of 81 crystal structures of the main protease 3CLpro, an important target for the design of drugs against COVID-19. The structures of the unliganded enzyme and its complexes with a number of inhibitors were determined by multiple research groups using different experimental approaches and conditions; the resulting structures span 13 different polymorphs representing seven space groups. The structures of the enzyme itself, all determined by molecular replacement, are highly similar, with the exception of one polymorph with a different inter-domain orientation. However, a number of complexes with bound inhibitors were found to pose significant problems. Some of these could be traced to faulty definitions of geometrical restraints for ligands and to the general problem of a lack of such information in the PDB depositions. Several problems with ligand definition in the PDB itself were also noted. In several cases extensive corrections to the models were necessary to adhere to the evidence of the electron-density maps. Taken together, this analysis of a large number of structures of a single, medically important protein, all determined within less than a year using modern experimental tools, should be useful in future studies of other systems of high interest to the biomedical community.

Synchrotron Radiation as a Tool for Macromolecular X-Ray Crystallography: a XXI Century Perspective.

Intense X-rays available at powerful synchrotron beamlines provide macromolecular crystallographers with an incomparable tool for investigating biological phenomena on an atomic scale. The resulting insights into the mechanism's underlying biological processes have played an essential role and shaped biomedical sciences during the last 30 years, considered the "golden age" of structural biology. In this review, we analyze selected aspects of the impact of synchrotron radiation on structural biology. Synchrotron beamlines have been used to determine over 70% of all macromolecular structures deposited into the Protein Data Bank (PDB). These structures were deposited by over 13,000 different research groups. Interestingly, despite the impressive advances in synchrotron technologies, the median resolution of macromolecular structures determined using synchrotrons has remained constant throughout the last 30 years, at about 2 Å. Similarly, the median times from the data collection to the deposition and release have not changed significantly. We describe challenges to reproducibility related to recording all relevant data and metadata during the synchrotron experiments, including diffraction images. Finally, we discuss some of the recent opinions suggesting a diminishing importance of X-ray crystallography due to impressive advances in Cryo-EM and theoretical modeling. We believe that synchrotrons of the future will increasingly evolve towards a life science center model, where X-ray crystallography, Cryo-EM, and other experimental and computational resources and knowledge are encompassed within a versatile research facility. The recent response of crystallographers to the COVID-19 pandemic suggests that X-ray crystallography conducted at synchrotron beamlines will continue to play an essential role in structural biology and drug discovery for years to come.

Celebrating the 75th birthday of Professor Wladek Minor, one of the most accomplished Polish-American structural biologists.

This paper describes the scientific career and accomplishments of Professor Wladek Minor, who holds an endowed chair at the University of Virginia in Charlottesville, USA. Prof. Minor is a coauthor of data processing software used by macromolecular crystallographers world-wide, as well as of structural biology servers and of a repository for raw diffraction data. He made major contributions to the validation of biostructural data, with special focus on drug design targets and reproducibility in biomedical research. He is among the most highly cited molecular biologists ever.

Covid-19.bioreproducibility.org: A web resource for SARS-CoV-2-related structural models.

The COVID-19 pandemic has triggered numerous scientific activities aimed at understanding the SARS-CoV-2 virus and ultimately developing treatments. Structural biologists have already determined hundreds of experimental X-ray, cryo-EM, and NMR structures of proteins and nucleic acids related to this coronavirus, and this number is still growing. To help biomedical researchers, who may not necessarily be experts in structural biology, navigate through the flood of structural models, we have created an online resource, covid19.bioreproducibility.org, that aggregates expert-verified information about SARS-CoV-2-related macromolecular models. In this article, we describe this web resource along with the suite of tools and methodologies used for assessing the structures presented therein.

State-of-the-Art Data Management: Improving the Reproducibility, Consistency, and Traceability of Structural Biology and in Vitro Biochemical Experiments.

Efficient and comprehensive data management is an indispensable component of modern scientific research and requires effective tools for all but the most trivial experiments. The LabDB system developed and used in our laboratory was originally designed to track the progress of a structure determination pipeline in several large National Institutes of Health (NIH) projects. While initially designed for structural biology experiments, its modular nature makes it easily applied in laboratories of various sizes in many experimental fields. Over many years, LabDB has transformed into a sophisticated system integrating a range of biochemical, biophysical, and crystallographic experimental data, which harvests data both directly from laboratory instruments and through human input via a web interface. The core module of the system handles many types of universal laboratory management data, such as laboratory personnel, chemical inventories, storage locations, and custom stock solutions. LabDB also tracks various biochemical experiments, including spectrophotometric and fluorescent assays, thermal shift assays, isothermal titration calorimetry experiments, and more. LabDB has been used to manage data for experiments that resulted in over 1200 deposits to the Protein Data Bank (PDB); the system is currently used by the Center for Structural Genomics of Infectious Diseases (CSGID) and several large laboratories. This chapter also provides examples of data mining analyses and warnings about incomplete and inconsistent experimental data. These features, together with its capabilities for detailed tracking, analysis, and auditing of experimental data, make the described system uniquely suited to inspect potential sources of irreproducibility in life sciences research.

Molecular determinants of vascular transport of dexamethasone in COVID-19 therapy.

Dexamethasone, a widely used corticosteroid, has recently been reported as the first drug to increase the survival chances of patients with severe COVID-19. Therapeutic agents, including dexamethasone, are mostly transported through the body by binding to serum albumin. Here, the first structure of serum albumin in complex with dexamethasone is reported. Dexamethasone binds to drug site 7, which is also the binding site for commonly used nonsteroidal anti-inflammatory drugs and testosterone, suggesting potentially problematic binding competition. This study bridges structural findings with an analysis of publicly available clinical data from Wuhan and suggests that an adjustment of the dexamethasone regimen should be further investigated as a strategy for patients affected by two major COVID-19 risk factors: low albumin levels and diabetes.

Molecular determinants of vascular transport of dexamethasone in COVID-19 therapy.

Dexamethasone, a widely used corticosteroid, has recently been reported as the first drug to increase the survival chances of patients with severe COVID-19. Therapeutic agents, including dexamethasone, are mostly transported through the body by binding to serum albumin. Herein, we report the first structure of serum albumin in complex with dexamethasone. We show that it binds to Drug Site 7, which is also the binding site for commonly used nonsteroidal anti-inflammatory drugs and testosterone, suggesting potentially problematic binding competition. This study bridges structural findings with our analysis of publicly available clinical data from Wuhan and suggests that an adjustment of dexamethasone regimen should be considered for patients affected by two major COVID-19 risk-factors: low albumin levels and diabetes.

Ligand-centered assessment of SARS-CoV-2 drug target models in the Protein Data Bank.

A bright spot in the SARS-CoV-2 (CoV-2) coronavirus pandemic has been the immediate mobilization of the biomedical community, working to develop treatments and vaccines for COVID-19. Rational drug design against emerging threats depends on well-established methodology, mainly utilizing X-ray crystallography, to provide accurate structure models of the macromolecular drug targets and of their complexes with candidates for drug development. In the current crisis, the structural biological community has responded by presenting structure models of CoV-2 proteins and depositing them in the Protein Data Bank (PDB), usually without time embargo and before publication. Since the structures from the first-line research are produced in an accelerated mode, there is an elevated chance of mistakes and errors, with the ultimate risk of hindering, rather than speeding up, drug development. In the present work, we have used model-validation metrics and examined the electron density maps for the deposited models of CoV-2 proteins and a sample of related proteins available in the PDB as of April 1, 2020. We present these results with the aim of helping the biomedical community establish a better-validated pool of data. The proteins are divided into groups according to their structure and function. In most cases, no major corrections were necessary. However, in several cases significant revisions in the functionally sensitive area of protein-inhibitor complexes or for bound ions justified correction, re-refinement, and eventually reversioning in the PDB. The re-refined coordinate files and a tool for facilitating model comparisons are available at https://covid-19.bioreproducibility.org. DATABASE: Validated models of CoV-2 proteins are available in a dedicated, publicly accessible web service https://covid-19.bioreproducibility.org.

Albumin-Based Transport of Nonsteroidal Anti-Inflammatory Drugs in Mammalian Blood Plasma.

Every day, hundreds of millions of people worldwide take nonsteroidal anti-inflammatory drugs (NSAIDs), often in conjunction with multiple other medications. In the bloodstream, NSAIDs are mostly bound to serum albumin (SA). We report the crystal structures of equine serum albumin complexed with four NSAIDs (ibuprofen, ketoprofen, etodolac, and nabumetone) and the active metabolite of nabumetone (6-methoxy-2-naphthylacetic acid, 6-MNA). These compounds bind to seven drug-binding sites on SA. These sites are generally well-conserved between equine and human SAs, but ibuprofen binds to both SAs in two drug-binding sites, only one of which is common. We also compare the binding of ketoprofen by equine SA to binding of it by bovine and leporine SAs. Our comparative analysis of known SA complexes with FDA-approved drugs clearly shows that multiple medications compete for the same binding sites, indicating possibilities for undesirable physiological effects caused by drug-drug displacement or competition with common metabolites. We discuss the consequences of NSAID binding to SA in a broader scientific and medical context, particularly regarding achieving desired therapeutic effects based on an individual's drug regimen.

Comparison of metal-bound and unbound structures of aminopeptidase B proteins from Escherichia coli and Yersinia pestis.

Protein degradation by aminopeptidases is involved in bacterial responses to stress. Escherichia coli produces two metal-dependent M17 family leucine aminopeptidases (LAPs), aminopeptidase A (PepA) and aminopeptidase B (PepB). Several structures have been solved for PepA as well as other bacterial M17 peptidases. Herein, we report the first structures of a PepB M17 peptidase. The E. coli PepB protein structure was determined at a resolution of 2.05 and 2.6 Å. One structure has both Zn2+ and Mn2+ , while the second structure has two Zn2+ ions bound to the active site. A 2.75 Å apo structure is also reported for PepB from Yersinia pestis. Both proteins form homohexamers, similar to the overall arrangement of PepA and other M17 peptidases. However, the divergent N-terminal domain in PepB is much larger resulting in a tertiary structure that is more expanded. Modeling of a dipeptide substrate into the C-terminal LAP domain reveals contacts that account for PepB to uniquely cleave after aspartate.

Trinuclear copper biocatalytic center forms an active site of thiocyanate dehydrogenase.

Biocatalytic copper centers are generally involved in the activation and reduction of dioxygen, with only few exceptions known. Here we report the discovery and characterization of a previously undescribed copper center that forms the active site of a copper-containing enzyme thiocyanate dehydrogenase (suggested EC 1.8.2.7) that was purified from the haloalkaliphilic sulfur-oxidizing bacterium of the genus Thioalkalivibrio ubiquitous in saline alkaline soda lakes. The copper cluster is formed by three copper ions located at the corners of a near-isosceles triangle and facilitates a direct thiocyanate conversion into cyanate, elemental sulfur, and two reducing equivalents without involvement of molecular oxygen. A molecular mechanism of catalysis is suggested based on high-resolution three-dimensional structures, electron paramagnetic resonance (EPR) spectroscopy, quantum mechanics/molecular mechanics (QM/MM) simulations, kinetic studies, and the results of site-directed mutagenesis.

Structural and biochemical analysis of Bacillus anthracis prephenate dehydrogenase reveals an unusual mode of inhibition by tyrosine via the ACT domain.

Tyrosine biosynthesis via the shikimate pathway is absent in humans and other animals, making it an attractive target for next-generation antibiotics, which is increasingly important due to the looming proliferation of multidrug-resistant pathogens. Tyrosine biosynthesis is also of commercial importance for the environmentally friendly production of numerous compounds, such as pharmaceuticals, opioids, aromatic polymers, and petrochemical aromatics. Prephenate dehydrogenase (PDH) catalyzes the penultimate step of tyrosine biosynthesis in bacteria: the oxidative decarboxylation of prephenate to 4-hydroxyphenylpyruvate. The majority of PDHs are competitively inhibited by tyrosine and consist of a nucleotide-binding domain and a dimerization domain. Certain PDHs, including several from pathogens on the World Health Organization priority list of antibiotic-resistant bacteria, possess an additional ACT domain. However, biochemical and structural knowledge was lacking for these enzymes. In this study, we successfully established a recombinant protein expression system for PDH from Bacillus anthracis (BaPDH), the causative agent of anthrax, and determined the structure of a BaPDH ternary complex with NAD+ and tyrosine, a binary complex with tyrosine, and a structure of an isolated ACT domain dimer. We also conducted detailed kinetic and biophysical analyses of the enzyme. We show that BaPDH is allosterically regulated by tyrosine binding to the ACT domains, resulting in an asymmetric conformation of the BaDPH dimer that sterically prevents prephenate binding to either active site. The presented mode of allosteric inhibition is unique compared to both the competitive inhibition established for other PDHs and to the allosteric mechanisms for other ACT-containing enzymes. This study provides new structural and mechanistic insights that advance our understanding of tyrosine biosynthesis in bacteria. ENZYMES: Prephenate dehydrogenase from Bacillus anthracis (PDH): EC database ID: 1.3.1.12. DATABASES: Coordinates and structure factors have been deposited in the Protein Data Bank (PDB) with accession numbers PDB ID: 6U60 (BaPDH complex with NAD+ and tyrosine), PDB ID: 5UYY (BaPDH complex with tyrosine), and PDB ID: 5V0S (BaPDH isolated ACT domain dimer). The diffraction images are available at http://proteindiffraction.org with DOIs: https://doi.org/10.18430/M35USC, https://doi.org/10.18430/M35UYY, and https://doi.org/10.18430/M35V0S.

The Integrated Resource for Reproducibility in Macromolecular Crystallography: Experiences of the first four years.

It has been increasingly recognized that preservation and public accessibility of primary experimental data are cornerstones necessary for the reproducibility of empirical sciences. In the field of molecular crystallography, many journals now recommend that authors of manuscripts presenting a new crystal structure should deposit their primary experimental data (X-ray diffraction images) to one of the dedicated resources created in recent years. Here, we describe our experiences developing the Integrated Resource for Reproducibility in Molecular Crystallography (IRRMC) and describe several examples of a crucial role that diffraction data can play in improving previously determined protein structures. In its first four years, several hundred crystallographers have deposited data from over 5200 diffraction experiments performed at over 60 different synchrotron beamlines or home sources all over the world. In addition to improving the resource and curating submitted data, we have been building a pipeline for extraction or, in some cases, reconstruction of the metadata necessary for seamless automated processing. Preliminary analysis indicates that about 95% of the archived data can be automatically reprocessed. A high rate of reprocessing success shows the feasibility of using the automated metadata extraction and automated processing as a validation step for the deposition of raw diffraction images. The IRRMC is guided by the Findable, Accessible, Interoperable, and Reusable data management principles.

Correction to: Classification, substrate specificity and structural features of D-2-hydroxyacid dehydrogenases: 2HADH knowledgebase.

Following publication of the original article [1], we have been notified that some important information was omitted by the authors from the Competing interests section. The declaration should read as below.