1
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Zirbel CL, Auffinger P. Lone Pair…π Contacts and Structure Signatures of r(UNCG) Tetraloops, Z-Turns, and Z-Steps: A WebFR3D Survey. Molecules 2022; 27:molecules27144365. [PMID: 35889236 PMCID: PMC9323530 DOI: 10.3390/molecules27144365] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2022] [Revised: 06/29/2022] [Accepted: 07/04/2022] [Indexed: 02/04/2023] Open
Abstract
Z-DNA and Z-RNA have long appeared as oddities to nucleic acid scientists. However, their Z-step constituents are recurrently observed in all types of nucleic acid systems including ribosomes. Z-steps are NpN steps that are isostructural to Z-DNA CpG steps. Among their structural features, Z-steps are characterized by the presence of a lone pair…π contact that involves the stacking of the ribose O4′ atom of the first nucleotide with the 3′-face of the second nucleotide. Recently, it has been documented that the CpG step of the ubiquitous r(UNCG) tetraloops is a Z-step. Accordingly, such r(UNCG) conformations were called Z-turns. It has also been recognized that an r(GAAA) tetraloop in appropriate conditions can shapeshift to an unusual Z-turn conformation embedding an ApA Z-step. In this report, we explore the multiplicity of RNA motifs based on Z-steps by using the WebFR3D tool to which we added functionalities to be able to retrieve motifs containing lone pair…π contacts. Many examples that underscore the diversity and universality of these motifs are provided as well as tutorial guidance on using WebFR3D. In addition, this study provides an extensive survey of crystallographic, cryo-EM, NMR, and molecular dynamics studies on r(UNCG) tetraloops with a critical view on how to conduct database searches and exploit their results.
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Affiliation(s)
- Craig L. Zirbel
- Department of Mathematics and Statistics, Bowling Green State University, Bowling Green, OH 43403, USA;
| | - Pascal Auffinger
- Architecture et Réactivité de l’ARN, UPR 9002, Institut de Biologie Moléculaire et Cellulaire du CNRS, Université de Strasbourg, 67084 Strasbourg, France
- Correspondence: ; Tel.: +33-3-8841-7049; Fax: +33-3-8860-2218
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2
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Helliwell JR. Pre- and Post-publication Verification for Reproducible Data Mining in Macromolecular Crystallography. Methods Mol Biol 2022; 2449:235-261. [PMID: 35507266 DOI: 10.1007/978-1-0716-2095-3_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Like an article narrative is deemed by an editor and referees to be worthy of being a version of record on acceptance as a publication, so must the underpinning data also be scrutinized before passing it as a version of record. Indeed without the underpinning data, a study and its conclusions cannot be reproduced at any stage of evaluation, pre- or post-publication. Likewise, an independent study without its own underpinning data also cannot be reproduced let alone be considered a replicate of the first study. The PDB is a modern marvel of achievement providing an organized open access to depositor and user of the data held there opening numerous applications. Methods for modeling protein structures and for determination of structures are still improving their precision, and artifacts of the method exist. So their accuracy is realized if they are reproduced by other methods. It is on such foundations that reproducible data mining is based. Data rates are expanding considerably be they at synchrotrons, the X-ray free electron lasers (XFELs), electron cryomicroscopes (cryoEM), or at the neutron facilities. The work of a person as a referee or user with a narrative and its underpinning data may well be complemented in future by artificial intelligence with machine learning, the former for specific refereeing and the latter for the more general validation, both ideally before publication. Examples are described involving rhenium theranostics, the anti-cancer platins and the SARS-CoV-2 main protease.
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Affiliation(s)
- John R Helliwell
- Department of Chemistry, University of Manchester, Manchester, UK.
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3
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Machine learning to estimate the local quality of protein crystal structures. Sci Rep 2021; 11:23599. [PMID: 34880321 PMCID: PMC8654820 DOI: 10.1038/s41598-021-02948-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 11/24/2021] [Indexed: 11/23/2022] Open
Abstract
Low-resolution electron density maps can pose a major obstacle in the determination and use of protein structures. Herein, we describe a novel method, called quality assessment based on an electron density map (QAEmap), which evaluates local protein structures determined by X-ray crystallography and could be applied to correct structural errors using low-resolution maps. QAEmap uses a three-dimensional deep convolutional neural network with electron density maps and their corresponding coordinates as input and predicts the correlation between the local structure and putative high-resolution experimental electron density map. This correlation could be used as a metric to modify the structure. Further, we propose that this method may be applied to evaluate ligand binding, which can be difficult to determine at low resolution.
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4
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Helliwell JR. Combining X-rays, neutrons and electrons, and NMR, for precision and accuracy in structure-function studies. Acta Crystallogr A Found Adv 2021; 77:173-185. [PMID: 33944796 PMCID: PMC8127390 DOI: 10.1107/s205327332100317x] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Accepted: 03/25/2021] [Indexed: 02/02/2023] Open
Abstract
The distinctive features of the physics-based probes used in understanding the structure of matter focusing on biological sciences, but not exclusively, are described in the modern context. This is set in a wider scope of holistic biology and the scepticism about `reductionism', what is called the `molecular level', and how to respond constructively. These topics will be set alongside the principles of accuracy and precision, and their boundaries. The combination of probes and their application together is the usual way of realizing accuracy. The distinction between precision and accuracy can be blurred by the predictive force of a precise structure, thereby lending confidence in its potential accuracy. These descriptions will be applied to the comparison of cryo and room-temperature protein crystal structures as well as the solid state of a crystal and the same molecules studied by small-angle X-ray scattering in solution and by electron microscopy on a sample grid. Examples will include: time-resolved X-ray Laue crystallography of an enzyme Michaelis complex formed directly in a crystal equivalent to in vivo; a new iodoplatin for radiation therapy predicted from studies of platin crystal structures; and the field of colouration of carotenoids, as an effective assay of function, i.e. their colouration, when unbound and bound to a protein. The complementarity of probes, as well as their combinatory use, is then at the foundation of real (biologically relevant), probe-artefacts-free, structure-function studies. The foundations of our methodologies are being transformed by colossal improvements in technologies of X-ray and neutron sources and their beamline instruments, as well as improved electron microscopes and NMR spectrometers. The success of protein structure prediction from gene sequence recently reported by CASP14 also opens new doors to change and extend the foundations of the structural sciences.
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Affiliation(s)
- John R. Helliwell
- Department of Chemistry, University of Manchester, Manchester, M13 9PL, United Kingdom
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5
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Auffinger P, Ennifar E, D'Ascenzo L. Deflating the RNA Mg 2+ bubble. Stereochemistry to the rescue! RNA (NEW YORK, N.Y.) 2020; 27:rna.076067.120. [PMID: 33268500 PMCID: PMC7901845 DOI: 10.1261/rna.076067.120] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Accepted: 11/20/2020] [Indexed: 05/03/2023]
Abstract
Proper evaluation of the ionic structure of biomolecular systems through X ray and cryo-EM techniques remains challenging but is essential for advancing our understanding of the underlying structure/activity/solvent relationships. However, numerous studies overestimate the number of Mg2+ in deposited structures due to assignment errors finding their origin in improper consideration of stereochemical rules. Herein, to tackle such issues, we re-evaluate the PDBid 6QNR and 6SJ6 models of the ribosome ionic structure. We establish that stereochemical principles need to be carefully pondered when evaluating ion binding features, even when K+ anomalous signals are available as it is the case for the 6QNR PDB entry. For ribosomes, assignment errors can result in misleading conceptions of their solvent structure. For instance, present stereochemical analysis result in a significant decrease of the number of assigned Mg2+ in 6QNR, suggesting that K+ and not Mg2+ is the prevalent ion in the ribosome 1st solvation shell. We stress that the use of proper stereochemical guidelines in combination or not with other identification techniques, such as those pertaining to the detection of transition metals, of some anions and of K+ anomalous signals, is critical for deflating the current Mg2+ bubble witnessed in many ribosome and other RNA structures. We also stress that for the identification of lighter ions such as Mg2+, Na+, …, for which no anomalous signals can be detected, stereochemistry coupled with high resolution structures (<2.4 Å) remain the best currently available option.
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6
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Brzezinski D, Dauter Z, Minor W, Jaskolski M. On the evolution of the quality of macromolecular models in the PDB. FEBS J 2020; 287:2685-2698. [PMID: 32311227 PMCID: PMC7340579 DOI: 10.1111/febs.15314] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2019] [Revised: 03/02/2020] [Accepted: 03/26/2020] [Indexed: 01/06/2023]
Abstract
Crystallographic models of biological macromolecules have been ranked using the quality criteria associated with them in the Protein Data Bank (PDB). The outcomes of this quality analysis have been correlated with time and with the journals that published papers based on those models. The results show that the overall quality of PDB structures has substantially improved over the last ten years, but this period of progress was preceded by several years of stagnation or even depression. Moreover, the study shows that the historically observed negative correlation between journal impact and the quality of structural models presented therein seems to disappear as time progresses.
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Affiliation(s)
- Dariusz Brzezinski
- Center for Biocrystallographic ResearchInstitute of Bioorganic ChemistryPolish Academy of SciencesPoznanPoland
- Institute of Computing SciencePoznan University of TechnologyPoland
- Center for Artificial Intelligence and Machine LearningPoznan University of TechnologyPoland
- Department of Molecular Physiology and Biological PhysicsUniversity of VirginiaCharlottesvilleVAUSA
| | - Zbigniew Dauter
- Synchrotron Radiation Research SectionMacromolecular Crystallography LaboratoryNational Cancer InstituteArgonne National LaboratoryArgonneILUSA
| | - Wladek Minor
- Department of Molecular Physiology and Biological PhysicsUniversity of VirginiaCharlottesvilleVAUSA
| | - Mariusz Jaskolski
- Center for Biocrystallographic ResearchInstitute of Bioorganic ChemistryPolish Academy of SciencesPoznanPoland
- Department of CrystallographyFaculty of ChemistryA. Mickiewicz UniversityPoznanPoland
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7
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Wlodawer A, Dauter Z, Shabalin IG, Gilski M, Brzezinski D, Kowiel M, Minor W, Rupp B, Jaskolski M. Ligand-centered assessment of SARS-CoV-2 drug target models in the Protein Data Bank. FEBS J 2020; 287:3703-3718. [PMID: 32418327 PMCID: PMC7276724 DOI: 10.1111/febs.15366] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Revised: 05/02/2020] [Accepted: 05/12/2020] [Indexed: 12/16/2022]
Abstract
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.
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Affiliation(s)
- Alexander Wlodawer
- Protein Structure Section, Macromolecular Crystallography Laboratory, NCI, Frederick, MD, USA
| | - Zbigniew Dauter
- Synchrotron Radiation Research Section, Macromolecular Crystallography Laboratory, NCI, Argonne National Laboratory, IL, USA
| | - Ivan G Shabalin
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Miroslaw Gilski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland.,Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
| | - Dariusz Brzezinski
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA.,Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.,Institute of Computing Science, Poznan University of Technology, Poland
| | - Marcin Kowiel
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
| | - Wladek Minor
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Bernhard Rupp
- k.-k. Hofkristallamt, San Diego, CA, USA.,Institute of Genetic Epidemiology, Medical University Innsbruck, Austria
| | - Mariusz Jaskolski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland.,Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
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8
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Grabowski M, Cymborowski M, Porebski PJ, Osinski T, Shabalin IG, Cooper DR, Minor W. The Integrated Resource for Reproducibility in Macromolecular Crystallography: Experiences of the first four years. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2019; 6:064301. [PMID: 31768399 PMCID: PMC6874509 DOI: 10.1063/1.5128672] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 11/04/2019] [Indexed: 05/05/2023]
Abstract
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.
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Affiliation(s)
| | | | - Przemyslaw J. Porebski
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charottesville, Virginia 22908, USA
| | - Tomasz Osinski
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charottesville, Virginia 22908, USA
| | | | | | - Wladek Minor
- Authors to whom correspondence should be addressed: and
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9
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Kruse H, Sponer J, Auffinger P. Comment on “Evaluating Unexpectedly Short Non-covalent Distances in X-ray Crystal Structures of Proteins with Electronic Structure Analysis”. J Chem Inf Model 2019; 59:3605-3608. [DOI: 10.1021/acs.jcim.9b00473] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Holger Kruse
- Institute of Biophysics of the Czech Academy of Sciences, Královopolská 135, CZ-61265 Brno, Czech Republic
| | - Jiri Sponer
- Institute of Biophysics of the Czech Academy of Sciences, Královopolská 135, CZ-61265 Brno, Czech Republic
| | - Pascal Auffinger
- Architecture et Réactivité de l’ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg 67084, France
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10
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Leonarski F, D'Ascenzo L, Auffinger P. Nucleobase carbonyl groups are poor Mg 2+ inner-sphere binders but excellent monovalent ion binders-a critical PDB survey. RNA (NEW YORK, N.Y.) 2019; 25:173-192. [PMID: 30409785 PMCID: PMC6348993 DOI: 10.1261/rna.068437.118] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Accepted: 10/16/2018] [Indexed: 05/04/2023]
Abstract
Precise knowledge of Mg2+ inner-sphere binding site properties is vital for understanding the structure and function of nucleic acid systems. Unfortunately, the PDB, which represents the main source of Mg2+ binding sites, contains a substantial number of assignment issues that blur our understanding of the functions of these ions. Here, following a previous study devoted to Mg2+ binding to nucleobase nitrogens, we surveyed nucleic acid X-ray structures from the PDB with resolutions ≤2.9 Å to classify the Mg2+ inner-sphere binding patterns to nucleotide carbonyl, ribose hydroxyl, cyclic ether, and phosphodiester oxygen atoms. From this classification, we derived a set of "prior-knowledge" nucleobase Mg2+ binding sites. We report that crystallographic examples of trustworthy nucleobase Mg2+ binding sites are fewer than expected since many of those are associated with misidentified Na+ or K+ We also emphasize that binding of Na+ and K+ to nucleic acids is much more frequent than anticipated. Overall, we provide evidence derived from X-ray structures that nucleobases are poor inner-sphere binders for Mg2+ but good binders for monovalent ions. Based on strict stereochemical criteria, we propose an extended set of guidelines designed to help in the assignment and validation of ions directly contacting nucleobase and ribose atoms. These guidelines should help in the interpretation of X-ray and cryo-EM solvent density maps. When borderline Mg2+ stereochemistry is observed, alternative placement of Na+, K+, or Ca2+ must be considered. We also critically examine the use of lanthanides (Yb3+, Tb3+) as Mg2+ substitutes in crystallography experiments.
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Affiliation(s)
- Filip Leonarski
- Swiss Light Source, Paul Scherrer Institut, Villigen PSI, 5232, Switzerland
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, 67084, France
| | - Luigi D'Ascenzo
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, 67084, France
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Pascal Auffinger
- Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du CNRS, Strasbourg, 67084, France
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11
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Wang H, Feng L, Webb GI, Kurgan L, Song J, Lin D. Critical evaluation of bioinformatics tools for the prediction of protein crystallization propensity. Brief Bioinform 2018; 19:838-852. [PMID: 28334201 PMCID: PMC6171492 DOI: 10.1093/bib/bbx018] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 01/19/2017] [Indexed: 12/11/2022] Open
Abstract
X-ray crystallography is the main tool for structural determination of proteins. Yet, the underlying crystallization process is costly, has a high attrition rate and involves a series of trial-and-error attempts to obtain diffraction-quality crystals. The Structural Genomics Consortium aims to systematically solve representative structures of major protein-fold classes using primarily high-throughput X-ray crystallography. The attrition rate of these efforts can be improved by selection of proteins that are potentially easier to be crystallized. In this context, bioinformatics approaches have been developed to predict crystallization propensities based on protein sequences. These approaches are used to facilitate prioritization of the most promising target proteins, search for alternative structural orthologues of the target proteins and suggest designs of constructs capable of potentially enhancing the likelihood of successful crystallization. We reviewed and compared nine predictors of protein crystallization propensity. Moreover, we demonstrated that integrating selected outputs from multiple predictors as candidate input features to build the predictive model results in a significantly higher predictive performance when compared to using these predictors individually. Furthermore, we also introduced a new and accurate predictor of protein crystallization propensity, Crysf, which uses functional features extracted from UniProt as inputs. This comprehensive review will assist structural biologists in selecting the most appropriate predictor, and is also beneficial for bioinformaticians to develop a new generation of predictive algorithms.
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Affiliation(s)
- Huilin Wang
- Department of Chemical Biology, College of Chemistry and Chemical Engineering, Xiamen University, China
| | | | - Geoffrey I Webb
- Monash Centre for Data Science, Faculty of Information Technology, Monash University, Australia
| | - Lukasz Kurgan
- Department of Computer Science, Virginia Commonwealth University, USA
| | - Jiangning Song
- Department of Biochemistry and Molecular Biology, Monash University, Australia
| | - Donghai Lin
- Department of Chemical Biology, College of Chemistry and Chemical Engineering, Xiamen University, China
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12
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Shabalin IG, Porebski PJ, Minor W. Refining the macromolecular model - achieving the best agreement with the data from X-ray diffraction experiment. CRYSTALLOGR REV 2018; 24:236-262. [PMID: 30416256 DOI: 10.1080/0889311x.2018.1521805] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Refinement of macromolecular X-ray crystal structures involves using complex software with hundreds of different settings. The complexity of underlying concepts and the sheer amount sof instructions may make it difficult for less experienced crystallographers to achieve optimal results in their refinements. This tutorial review offers guidelines for choosing the best settings for the reciprocal-space refinement of macromolecular models and provides practical tips for manual model correction. To help aspiring crystallographers navigate the process, some of the most practically important concepts of protein structure refinement are described. Among the topics covered are the use and purpose of R-free, geometrical restraints, restraints on atomic displacement parameters (ADPs), refinement weights, various parametrizations of ADPs (full anisotropic refinement and TLS), and omit maps. We also give practical tips for manual model correction in Coot, modelling of side-chains with poor or missing density, and ligand identification, fitting, and refinement.
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Affiliation(s)
- Ivan G Shabalin
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, United States.,Center for Structural Genomics of Infectious Diseases (CSGID), Charlottesville, VA, 22908, United States
| | - Przemyslaw J Porebski
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, United States.,Center for Structural Genomics of Infectious Diseases (CSGID), Charlottesville, VA, 22908, United States
| | - Wladek Minor
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, United States.,Center for Structural Genomics of Infectious Diseases (CSGID), Charlottesville, VA, 22908, United States
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13
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Raczynska JE, Shabalin IG, Minor W, Wlodawer A, Jaskolski M. A close look onto structural models and primary ligands of metallo-β-lactamases. Drug Resist Updat 2018; 40:1-12. [PMID: 30466711 PMCID: PMC6260963 DOI: 10.1016/j.drup.2018.08.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 08/14/2018] [Accepted: 08/16/2018] [Indexed: 10/28/2022]
Abstract
β-Lactamases are hydrolytic enzymes capable of opening the β-lactam ring of antibiotics such as penicillin, thus endowing the bacteria that produce them with antibiotic resistance. Of particular medical concern are metallo-β-lactamases (MBLs), with an active site built around coordinated Zn cations. MBLs are pan-reactive enzymes that can break down almost all classes of β-lactams, including such last-resort antibiotics as carbapenems. They are not only broad-spectrum-reactive but are often plasmid-borne (e.g., the New Delhi enzyme, NDM), and can spread horizontally even among unrelated bacteria. Acquired MBLs are encoded by mobile genetic elements, which often include other resistance genes, making the microbiological situation particularly alarming. There is an urgent need to develop MBL inhibitors in order to rescue our antibiotic armory. A number of such efforts have been undertaken, most notably using the 3D structures of various MBLs as drug-design targets. Structure-guided drug discovery depends on the quality of the structures that are collected in the Protein Data Bank (PDB) and on the consistency of the information in dedicated β-lactamase databases. We conducted a careful review of the crystal structures of class B β-lactamases, concluding that the quality of these structures varies widely, especially in the regions where small molecules interact with the macromolecules. In a number of examples the interpretation of the bound ligands (e.g., inhibitors, substrate/product analogs) is doubtful or even incorrect, and it appears that in some cases the modeling of ligands was not supported by electron density. For ten MBL structures, alternative interpretations of the original diffraction data could be proposed and the new models have been deposited in the PDB. In four cases, these models, prepared jointly with the authors of the original depositions, superseded the previous deposits. This review emphasizes the importance of critical assessment of structural models describing key drug design targets at the level of the raw experimental data. Since the structures reviewed here are the basis for ongoing design of new MBL inhibitors, it is important to identify and correct the problems with ambiguous crystallographic interpretations, thus enhancing reproducibility in this highly medically relevant area.
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Affiliation(s)
- Joanna E Raczynska
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
| | - Ivan G Shabalin
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA; Center for Structural Genomics of Infectious Diseases, Charlottesville, VA 22908, USA
| | - Wladek Minor
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA; Center for Structural Genomics of Infectious Diseases, Charlottesville, VA 22908, USA
| | - Alexander Wlodawer
- Protein Structure Section, Macromolecular Crystallography Laboratory, National Cancer Institute, Frederick, MD 21702, USA
| | - Mariusz Jaskolski
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland; Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland.
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14
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Wlodawer A, Dauter Z, Porebski PJ, Minor W, Stanfield R, Jaskolski M, Pozharski E, Weichenberger CX, Rupp B. Detect, correct, retract: How to manage incorrect structural models. FEBS J 2018; 285:444-466. [PMID: 29113027 PMCID: PMC5799025 DOI: 10.1111/febs.14320] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2017] [Accepted: 11/01/2017] [Indexed: 12/13/2022]
Abstract
The massive technical and computational progress of biomolecular crystallography has generated some adverse side effects. Most crystal structure models, produced by crystallographers or well-trained structural biologists, constitute useful sources of information, but occasional extreme outliers remind us that the process of structure determination is not fail-safe. The occurrence of severe errors or gross misinterpretations raises fundamental questions: Why do such aberrations emerge in the first place? How did they evade the sophisticated validation procedures which often produce clear and dire warnings, and why were severe errors not noticed by the depositors themselves, their supervisors, referees and editors? Once detected, what can be done to either correct, improve or eliminate such models? How do incorrect models affect the underlying claims or biomedical hypotheses they were intended, but failed, to support? What is the long-range effect of the propagation of such errors? And finally, what mechanisms can be envisioned to restore the validity of the scientific record and, if necessary, retract publications that are clearly invalidated by the lack of experimental evidence? We suggest that cognitive bias and flawed epistemology are likely at the root of the problem. By using examples from the published literature and from public repositories such as the Protein Data Bank, we provide case summaries to guide correction or improvement of structural models. When strong claims are unsustainable because of a deficient crystallographic model, removal of such a model and even retraction of the affected publication are necessary to restore the integrity of the scientific record.
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Affiliation(s)
- Alexander Wlodawer
- Protein Structure Section, Macromolecular Crystallography Laboratory, National Cancer Institute, Frederick, MD, 21702, USA
| | - Zbigniew Dauter
- Synchrotron Radiation Research Section, Macromolecular Crystallography Laboratory, National Cancer Institute, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Przemyslaw J. Porebski
- Department of Molecular Physiology and Biological Physics, University of Virginia, 1340 Jefferson Park Avenue, Charlottesville, VA, 22908, USA
| | - Wladek Minor
- Department of Molecular Physiology and Biological Physics, University of Virginia, 1340 Jefferson Park Avenue, Charlottesville, VA, 22908, USA
| | - Robyn Stanfield
- Department of Structural and Computational Biology, BCC206, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA, 92037, USA
| | - Mariusz Jaskolski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Umultowska 89b, Poznan, 61-614, Poland
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, Poznan, 61-704, Poland
| | - Edwin Pozharski
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA
| | | | - Bernhard Rupp
- CVMO, k.-k.Hofkristallamt, 991 Audrey Place, Vista, CA, 92084, USA
- Department of Genetic Epidemiology, Medical University Innsbruck, Schöpfstr. 41, Innsbruck, 6020, Austria
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15
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Martin SJ. The FEBS Journal in 2018 - putting a bit of color in your life, and your figures. FEBS J 2018; 285:4-7. [PMID: 29314600 DOI: 10.1111/febs.14365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Seamus Martin holds the Smurfit Chair of Medical Genetics at the Smurfit Institute of Genetics, Trinity College Dublin, Ireland. He works on all aspects of cell death control and is especially interested in the links between cell death, cell stress and inflammation. He received the GlaxoSmithKline Award of The Biochemical Society (2006) and The RDS-Irish Times Boyle Medal (2015) for his work on the role of caspases in apoptosis and was elected to the Royal Irish Academy in 2006 and EMBO in 2009. He is the Editor-in-Chief of The FEBS Journal since 2014.
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Affiliation(s)
- Seamus J Martin
- The FEBS Journal Editorial Office, Cambridge, UK.,Department of Genetics, Trinity College, Dublin, Ireland
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16
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Wlodawer A. Online tools for enhancing presentation, understanding, and retention of 3D structural data. FEBS J 2017; 284:3974-3976. [DOI: 10.1111/febs.14316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alexander Wlodawer
- Macromolecular Crystallography Laboratory; National Cancer Institute; Frederick MD USA
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17
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Helliwell JR, McMahon B, Guss JM, Kroon-Batenburg LMJ. The science is in the data. IUCRJ 2017; 4:714-722. [PMID: 29123672 PMCID: PMC5668855 DOI: 10.1107/s2052252517013690] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 09/24/2017] [Indexed: 05/22/2023]
Abstract
Understanding published research results should be through one's own eyes and include the opportunity to work with raw diffraction data to check the various decisions made in the analyses by the original authors. Today, preserving raw diffraction data is technically and organizationally viable at a growing number of data archives, both centralized and distributed, which are empowered to register data sets and obtain a preservation descriptor, typically a 'digital object identifier'. This introduces an important role of preserving raw data, namely understanding where we fail in or could improve our analyses. Individual science area case studies in crystallography are provided.
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Affiliation(s)
- John R. Helliwell
- School of Chemistry, University of Manchester, Manchester M13 9PL, England
| | - Brian McMahon
- International Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England
| | - J. Mitchell Guss
- School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia
| | - Loes M. J. Kroon-Batenburg
- Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, CH 3584 Utrecht, The Netherlands
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18
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Porebski PJ, Sroka P, Zheng H, Cooper DR, Minor W. Molstack-Interactive visualization tool for presentation, interpretation, and validation of macromolecules and electron density maps. Protein Sci 2017; 27:86-94. [PMID: 28815771 DOI: 10.1002/pro.3272] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Revised: 08/11/2017] [Accepted: 08/14/2017] [Indexed: 11/07/2022]
Abstract
Our understanding of the world of biomolecular structures is based upon the interpretation of macromolecular models, of which ∼90% are an interpretation of electron density maps. This structural information guides scientific progress and exploration in many biomedical disciplines. The Protein Data Bank's web portals have made these structures available for mass scientific consumption and greatly broaden the scope of information presented in scientific publications. The portals provide numerous quality metrics; however, the portion of the structure that is most vital for interpretation of the function may have the most difficult to interpret electron density and this ambiguity is not reflected by any single metric. The possible consequences of basing research on suboptimal models make it imperative to inspect the agreement of a model with its experimental evidence. Molstack, a web-based interactive publishing platform for structural data, allows users to present density maps and structural models by displaying a collection of maps and models, including different interpretation of one's own data, re-refinements, and corrections of existing structures. Molstack organizes the sharing and dissemination of these structural models along with their experimental evidence as an interactive session. Molstack was designed with three groups of users in mind; researchers can present the evidence of their interpretation, reviewers and readers can independently judge the experimental evidence of the authors' conclusions, and other researchers can present or even publish their new hypotheses in the context of prior results. The server is available at http://molstack.bioreproducibility.org.
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Affiliation(s)
- Przemyslaw J Porebski
- Department of Biological Physics & Molecular Physiology, University of Virginia, Charlottesville, Virginia
| | - Piotr Sroka
- Department of Biological Physics & Molecular Physiology, University of Virginia, Charlottesville, Virginia
| | - Heping Zheng
- Department of Biological Physics & Molecular Physiology, University of Virginia, Charlottesville, Virginia
| | - David R Cooper
- Department of Biological Physics & Molecular Physiology, University of Virginia, Charlottesville, Virginia
| | - Wladek Minor
- Department of Biological Physics & Molecular Physiology, University of Virginia, Charlottesville, Virginia
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19
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Helliwell JR. New developments in crystallography: exploring its technology, methods and scope in the molecular biosciences. Biosci Rep 2017; 37:BSR20170204. [PMID: 28572170 PMCID: PMC6434086 DOI: 10.1042/bsr20170204] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Revised: 05/31/2017] [Accepted: 06/01/2017] [Indexed: 12/16/2022] Open
Abstract
Since the Protein Data Bank (PDB) was founded in 1971, there are now over 120,000 depositions, the majority of which are from X-ray crystallography and 90% of those made use of synchrotron beamlines. At the Cambridge Structure Database (CSD), founded in 1965, there are more than 800,000 'small molecule' crystal structure depositions and a very large number of those are relevant in the biosciences as ligands or cofactors. The technology for crystal structure analysis is still developing rapidly both at synchrotrons and in home labs. Determination of the details of the hydrogen atoms in biological macromolecules is well served using neutrons as probe. Large multi-macromolecular complexes cause major challenges to crystallization; electrons as probes offer unique advantages here. Methods developments naturally accompany technology change, mainly incremental but some, such as the tuneability, intensity and collimation of synchrotron radiation, have effected radical changes in capability of biological crystallography. In the past few years, the X-ray laser has taken X-ray crystallography measurement times into the femtosecond range. In terms of applications many new discoveries have been made in the molecular biosciences. The scope of crystallographic techniques is indeed very wide. As examples, new insights into chemical catalysis of enzymes and relating ligand bound structures to thermodynamics have been gained but predictive power is seen as not yet achieved. Metal complexes are also an emerging theme for biomedicine applications. Our studies of coloration of live and cooked lobsters proved to be an unexpected favourite with the public and schoolchildren. More generally, public understanding of the biosciences and crystallography's role within the field have been greatly enhanced by the United Nations International Year of Crystallography coordinated by the International Union of Crystallography. This topical review describes each of these areas along with illustrative results to document the scope of each methodology.
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20
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Yao S, Flight RM, Rouchka EC, Moseley HNB. Perspectives and expectations in structural bioinformatics of metalloproteins. Proteins 2017; 85:938-944. [PMID: 28168746 PMCID: PMC5389925 DOI: 10.1002/prot.25263] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 01/16/2017] [Accepted: 01/31/2017] [Indexed: 01/21/2023]
Abstract
Recent papers highlight the presence of large numbers of compressed angles in metal ion coordination geometries for metalloprotein entries in the worldwide Protein Data Bank, due mainly to multidentate coordination. The prevalence of these compressed angles has raised the controversial idea that significantly populated aberrant or even novel coordination geometries may exist. Some of these papers have undergone severe criticism, apparently due to views held that only canonical coordination geometries exist in significant numbers. While criticism of controversial ideas is warranted and to be expected, we believe that a line was crossed where unfair criticism was put forth to discredit an inconvenient result that compressed angles exist in large numbers, which does not support the dogmatic canonical coordination geometry view. We present a review of the major controversial results and their criticisms, pointing out both good suggestions that have been incorporated in new analyses, but also unfair criticism that was put forth to support a particular view. We also suggest that better science is enabled through: (i) a more collegial and collaborative approach in future critical reviews and (ii) the requirement for a description of methods and data including source code and visualizations that enables full reproducibility of results. Proteins 2017; 85:938-944. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Sen Yao
- School of Interdisciplinary and Graduate Studies, University of Louisville, Louisville, Kentucky, 40292
- Department of Computer Engineering and Computer Science, University of Louisville, Louisville, Kentucky, 40292
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, 40356
- Markey Cancer Center, University of Kentucky, Lexington, Kentucky, 40356
- Center for Environmental and Systems Biochemistry, University of Kentucky, Lexington, Kentucky, 40356
| | - Robert M Flight
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, 40356
- Markey Cancer Center, University of Kentucky, Lexington, Kentucky, 40356
- Center for Environmental and Systems Biochemistry, University of Kentucky, Lexington, Kentucky, 40356
| | - Eric C Rouchka
- School of Interdisciplinary and Graduate Studies, University of Louisville, Louisville, Kentucky, 40292
- Department of Computer Engineering and Computer Science, University of Louisville, Louisville, Kentucky, 40292
| | - Hunter N B Moseley
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky, 40356
- Markey Cancer Center, University of Kentucky, Lexington, Kentucky, 40356
- Center for Environmental and Systems Biochemistry, University of Kentucky, Lexington, Kentucky, 40356
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21
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Groom CR, Cole JC. The use of small-molecule structures to complement protein-ligand crystal structures in drug discovery. Acta Crystallogr D Struct Biol 2017; 73:240-245. [PMID: 28291759 PMCID: PMC5349436 DOI: 10.1107/s2059798317000675] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 01/13/2017] [Indexed: 11/10/2022] Open
Abstract
Many ligand-discovery stories tell of the use of structures of protein-ligand complexes, but the contribution of structural chemistry is such a core part of finding and improving ligands that it is often overlooked. More than 800 000 crystal structures are available to the community through the Cambridge Structural Database (CSD). Individually, these structures can be of tremendous value and the collection of crystal structures is even more helpful. This article provides examples of how small-molecule crystal structures have been used to complement those of protein-ligand complexes to address challenges ranging from affinity, selectivity and bioavailability though to solubility.
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Affiliation(s)
- Colin R. Groom
- Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, England
| | - Jason C. Cole
- Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, England
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22
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Weichenberger CX, Pozharski E, Rupp B. Twilight reloaded: the peptide experience. Acta Crystallogr D Struct Biol 2017; 73:211-222. [PMID: 28291756 PMCID: PMC5349433 DOI: 10.1107/s205979831601620x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2016] [Accepted: 10/12/2016] [Indexed: 01/20/2024] Open
Abstract
The de facto commoditization of biomolecular crystallography as a result of almost disruptive instrumentation automation and continuing improvement of software allows any sensibly trained structural biologist to conduct crystallographic studies of biomolecules with reasonably valid outcomes: that is, models based on properly interpreted electron density. Robust validation has led to major mistakes in the protein part of structure models becoming rare, but some depositions of protein-peptide complex structure models, which generally carry significant interest to the scientific community, still contain erroneous models of the bound peptide ligand. Here, the protein small-molecule ligand validation tool Twilight is updated to include peptide ligands. (i) The primary technical reasons and potential human factors leading to problems in ligand structure models are presented; (ii) a new method used to score peptide-ligand models is presented; (iii) a few instructive and specific examples, including an electron-density-based analysis of peptide-ligand structures that do not contain any ligands, are discussed in detail; (iv) means to avoid such mistakes and the implications for database integrity are discussed and (v) some suggestions as to how journal editors could help to expunge errors from the Protein Data Bank are provided.
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Affiliation(s)
| | - Edwin Pozharski
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Bernhard Rupp
- k.k. Hofkristallamt, 991 Audrey Place, Vista, CA 92084, USA
- Department of Genetic Epidemiology, Medical University Innsbruck, Schöpfstrasse 41, A-6020 Innsbruck, Austria
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23
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Pozharski E, Deller MC, Rupp B. Validation of Protein-Ligand Crystal Structure Models: Small Molecule and Peptide Ligands. Methods Mol Biol 2017; 1607:611-625. [PMID: 28573591 DOI: 10.1007/978-1-4939-7000-1_25] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Models of target proteins in complex with small molecule ligands or peptide ligands are of significant interest to the biomedical research community. Structure-guided lead discovery and structure-based drug design make extensive use of such models. The bound ligands comprise only a small fraction of the total X-ray scattering mass, and therefore particular care must be taken to properly validate the atomic model of the ligand as experimental data can often be scarce. The ligand model must be validated against both the primary experimental data and the local environment, specifically: (1) the primary evidence in the form of the electron density, (2) examined for reasonable stereochemistry, and (3) the chemical plausibility of the binding interactions must be inspected. Tools that assist the researcher in the validation process are presented.
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Affiliation(s)
- Edwin Pozharski
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Marc C Deller
- Stanford ChEM-H, Macromolecular Structure Knowledge Center, Stanford University, Shriram Center, 443 Via Ortega, Room 097, MC5082, Stanford, CA, 94305-4125, USA
| | - Bernhard Rupp
- k.-k. Hofkristallamt, 991 Audrey Place, Vista, CA, 92084, USA.
- Department of Genetic Epidemiology, Medical University Innsbruck, Schöpfstr. 41, Innsbruck, 6020, Austria.
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24
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Naschberger A, Fürnrohr BG, Lenac Rovis T, Malic S, Scheffzek K, Dieplinger H, Rupp B. The N14 anti-afamin antibody Fab: a rare V L1 CDR glycosylation, crystallographic re-sequencing, molecular plasticity and conservative versus enthusiastic modelling. Acta Crystallogr D Struct Biol 2016; 72:1267-1280. [PMID: 27917827 PMCID: PMC5137224 DOI: 10.1107/s205979831601723x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Accepted: 10/26/2016] [Indexed: 12/31/2022] Open
Abstract
The monoclonal antibody N14 is used as a detection antibody in ELISA kits for the human glycoprotein afamin, a member of the albumin family, which has recently gained interest in the capture and stabilization of Wnt signalling proteins, and for its role in metabolic syndrome and papillary thyroid carcinoma. As a rare occurrence, the N14 Fab is N-glycosylated at Asn26L at the onset of the VL1 antigen-binding loop, with the α-1-6 core fucosylated complex glycan facing out of the L1 complementarity-determining region. The crystal structures of two non-apparent (pseudo) isomorphous crystals of the N14 Fab were analyzed, which differ significantly in the elbow angles, thereby cautioning against the overinterpretation of domain movements upon antigen binding. In addition, the map quality at 1.9 Å resolution was sufficient to crystallographically re-sequence the variable VL and VH domains and to detect discrepancies in the hybridoma-derived sequence. Finally, a conservatively refined parsimonious model is presented and its statistics are compared with those from a less conservatively built model that has been modelled more enthusiastically. Improvements to the PDB validation reports affecting ligands, clashscore and buried surface calculations are suggested.
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Affiliation(s)
- Andreas Naschberger
- Division of Biological Chemistry, Medical University of Innsbruck, Innrain 80, 6020 Innsbruck, Austria
| | - Barbara G. Fürnrohr
- Division of Biological Chemistry, Medical University of Innsbruck, Innrain 80, 6020 Innsbruck, Austria
| | - Tihana Lenac Rovis
- Center for Proteomics, University of Rijeka, B. Branchetta 20, 51000 Rijeka, Croatia
| | - Suzana Malic
- Center for Proteomics, University of Rijeka, B. Branchetta 20, 51000 Rijeka, Croatia
| | - Klaus Scheffzek
- Division of Biological Chemistry, Medical University of Innsbruck, Innrain 80, 6020 Innsbruck, Austria
| | - Hans Dieplinger
- Division of Genetic Epidemiology, Medical University of Innsbruck, Schöpfstrasse 41, 6020 Innsbruck, Austria
- Vitateq Biotechnology GmbH, Innrain 66, 6020 Innsbruck, Austria
| | - Bernhard Rupp
- Division of Genetic Epidemiology, Medical University of Innsbruck, Schöpfstrasse 41, 6020 Innsbruck, Austria
- CVMO, k.-k. Hofkristallamt, 991 Audrey Place, Vista, CA 92084, USA
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25
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Drozdzal P, Gilski M, Jaskolski M. Ultrahigh-resolution centrosymmetric crystal structure of Z-DNA reveals the massive presence of alternate conformations. ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY 2016; 72:1203-1211. [PMID: 27841753 DOI: 10.1107/s205979831601679x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 10/19/2016] [Indexed: 01/29/2023]
Abstract
The self-complementary d(CGCGCG) hexanucleotide was synthesized with both D-2'-deoxyribose (the natural enantiomer) and L-2'-deoxyribose, and the two enantiomers were mixed in racemic (1:1) proportions and crystallized, producing a new crystal form with C2/c symmetry that diffracted X-rays to 0.78 Å resolution. The structure was solved by direct, dual-space and molecular-replacement methods and was refined to an R factor of 13.86%. The asymmetric unit of the crystal contains one Z-DNA duplex and three Mg2+ sites. The crystal structure is comprised of both left-handed (D-form) and right-handed (L-form) Z-DNA duplexes and shows an unexpectedly high degree of structural disorder, which is manifested by the presence of alternate conformations along the DNA backbone chains as well as at four nucleobases (including one base pair) modelled in double conformations. The crystal packing of the presented D/L-DNA-Mg2+ structure exhibits novel DNA hydration patterns and an unusual arrangement of the DNA helices in the unit cell. The paper describes the structure in detail, concentrating on the mode of disorder, and compares the crystal packing of the racemic d(CGCGCG)2 duplex with those of other homochiral and heterochiral Z-DNA structures.
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Affiliation(s)
- Pawel Drozdzal
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
| | - Miroslaw Gilski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
| | - Mariusz Jaskolski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
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26
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Minor W, Dauter Z, Jaskolski M. The young person's guide to the PDB. Postepy Biochem 2016; 62:242-249. [PMID: 28132477 PMCID: PMC5610703 DOI: 10.18388/pb.2016_1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2016] [Accepted: 07/06/2016] [Indexed: 06/06/2023]
Abstract
The Protein Data Bank (PDB), created in 1971 when merely seven protein crystal structures were known, today holds over 120, 000 experimentally-determined three-dimensional models of macromolecules, including gigantic structures comprised of hundreds of thousands of atoms, such as ribosomes and viruses. Most of the deposits come from X-ray crystallography experiments, with important contributions also made by NMR spectroscopy and, recently, by the fast growing Cryo-Electron Microscopy. Although the determination of a macromolecular crystal structure is now facilitated by advanced experimental tools and by sophisticated software, it is still a highly complicated research process requiring specialized training, skill, experience and a bit of luck. Understanding the plethora of structural information provided by the PDB requires that its users (consumers) have at least a rudimentary initiation. This is the purpose of this educational overview.
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Affiliation(s)
- Wladek Minor
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA
| | - Zbigniew Dauter
- Macromolecular Crystallography Laboratory, National Cancer Institute, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Mariusz Jaskolski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
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