Data curation practices of the Crystallography Open Database (COD) are described with additional focus being placed on the formal validation using the Crystallographic Information Framework (CIF). ...The cif_validate program, capable of validating CIF files against both the DDL1 and the DDLm dictionaries, is presented and used to process the entirety of the COD. Validation results collected from over 450 000 CIF files are demonstrated to be a useful resource in the data maintenance process as well as the development of the underlying ontologies. A set of programs intended to aid in the dictionary migration from DDL1 to DDLm is also presented.
Data curation practices of the Crystallography Open Database are described with greater focus being placed on the cif_validate program, capable of validating crystallographic information files against both DDL1 and DDLm dictionaries.
Identifying the probable positions of the protein side-chains is one of the protein modelling steps that can improve the prediction of protein-ligand and protein-protein interactions. Most of the ...strategies predicting the side-chain conformations use predetermined dihedral angle lists, also called rotamer libraries, that are usually generated from a subset of high-quality protein structures. Although these methods are fast to apply, they tend to average out geometries instead of taking into account the surrounding atoms and molecules and ignore structures not included in the selected subset. Such simplifications can result in inaccuracies when predicting possible side-chain atom positions.
We propose an approach that takes into account both of these circumstances by scanning through sterically accessible side-chain conformations and generating dihedral angle libraries specific to the target proteins. The method avoids the drawbacks of lacking conformations due to unusual or rare protein structures and successfully suggests potential rotamers with average RMSD closer to the experimentally determined side-chain atom positions than other widely used rotamer libraries.
The technique is implemented in open-source software package rotag and available at GitHub: https://www.github.com/agrybauskas/rotag, under GNU Lesser General Public License.
AceDRG: a stereochemical description generator for ligands Long, Fei; Nicholls, Robert A.; Emsley, Paul ...
Acta crystallographica. Section D, Structural biology,
February 2017, 2017-02-01, 20170201, Letnik:
73, Številka:
2
Journal Article
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The program AceDRG is designed for the derivation of stereochemical information about small molecules. It uses local chemical and topological environment‐based atom typing to derive and organize bond ...lengths and angles from a small‐molecule database: the Crystallography Open Database (COD). Information about the hybridization states of atoms, whether they belong to small rings (up to seven‐membered rings), ring aromaticity and nearest‐neighbour information is encoded in the atom types. All atoms from the COD have been classified according to the generated atom types. All bonds and angles have also been classified according to the atom types and, in a certain sense, bond types. Derived data are tabulated in a machine‐readable form that is freely available from CCP4. AceDRG can also generate stereochemical information, provided that the basic bonding pattern of a ligand is known. The basic bonding pattern is perceived from one of the computational chemistry file formats, including SMILES, mmCIF, SDF MOL and SYBYL MOL2 files. Using the bonding chemistry, atom types, and bond and angle tables generated from the COD, AceDRG derives the `ideal' bond lengths, angles, plane groups, aromatic rings and chirality information, and writes them to an mmCIF file that can be used by the refinement program REFMAC5 and the model‐building program Coot. Other refinement and model‐building programs such as PHENIX and BUSTER can also use these files. AceDRG also generates one or more coordinate sets corresponding to the most favourable conformation(s) of a given ligand. AceDRG employs RDKit for chemistry perception and for initial conformation generation, as well as for the interpretation of SMILES strings, SDF MOL and SYBYL MOL2 files.
The program AceDRG generates accurate stereochemical descriptions, and one or more conformations, of a given ligand. The program also analyses entries and extracts local environment‐dependent atom types, bonds and angles from the Crystallography Open Database.
Using an open-access distribution model, the Crystallography Open Database (COD, http://www.crystallography.net) collects all known 'small molecule small to medium sized unit cell' crystal structures ...and makes them available freely on the Internet. As of today, the COD has aggregated ∼150 000 structures, offering basic search capabilities and the possibility to download the whole database, or parts thereof using a variety of standard open communication protocols. A newly developed website provides capabilities for all registered users to deposit published and so far unpublished structures as personal communications or pre-publication depositions. Such a setup enables extension of the COD database by many users simultaneously. This increases the possibilities for growth of the COD database, and is the first step towards establishing a world wide Internet-based collaborative platform dedicated to the collection and curation of structural knowledge.
Computer descriptions of chemical molecular connectivity are necessary for searching chemical databases and for predicting chemical properties from molecular structure. In this article, the ongoing ...work to describe the chemical connectivity of entries contained in the Crystallography Open Database (COD) in SMILES format is reported. This collection of SMILES is publicly available for chemical (substructure) search or for any other purpose on an open-access basis, as is the COD itself. The conventions that have been followed for the representation of compounds that do not fit into the valence bond theory are outlined for the most frequently found cases. The procedure for getting the SMILES out of the CIF files starts with checking whether the atoms in the asymmetric unit are a chemically acceptable image of the compound. When they are not (molecule in a symmetry element, disorder, polymeric species,etc.), the previously published cif_molecule program is used to get such image in many cases. The program package
Open Babel
is then applied to get SMILES strings from the CIF files (either those directly taken from the COD or those produced by cif_molecule when applicable). The results are then checked and/or fixed by a human editor, in a computer-aided task that at present still consumes a great deal of human time. Even if the procedure still needs to be improved to make it more automatic (and hence faster), it has already yielded more than 160,000 curated chemical structures and the purpose of this article is to announce the existence of this work to the chemical community as well as to spread the use of its results.
Crystallographic investigations deliver high‐accuracy information about positions of atoms in crystal unit cells. For chemists, however, the structure of a molecule is most often of interest. The ...structure must thus be reconstructed from crystallographic files using symmetry information and chemical properties of atoms. Most existing algorithms faithfully reconstruct separate molecules but not the overall stoichiometry of the complex present in a crystal. Here, an algorithm that can reconstruct stoichiometrically correct multimolecular ensembles is described. This algorithm uses only the crystal symmetry information for determining molecule numbers and their stoichiometric ratios. The algorithm can be used by chemists and crystallographers as a standalone implementation for investigating above‐molecular ensembles or as a function implemented in graphical crystal analysis software. The greatest envisaged benefit of the algorithm, however, is for the users of large crystallographic and chemical databases, since it will permit database maintainers to generate stoichiometrically correct chemical representations of crystal structures automatically and to match them against chemical databases, enabling multidisciplinary searches across multiple databases.
A syntax‐correcting CIF parser, COD::CIF::Parser, is presented that can parse CIF 1.1 files and accurately report the position and the nature of the discovered syntactic problems. In addition, the ...parser is able to automatically fix the most common and the most obvious syntactic deficiencies of the input files. Bindings for Perl, C and Python programming environments are available. Based on COD::CIF::Parser, the cod‐tools package for manipulating the CIFs in the Crystallography Open Database (COD) has been developed. The cod‐tools package has been successfully used for continuous updates of the data in the automated COD data deposition pipeline, and to check the validity of COD data against the IUCr data validation guidelines. The performance, capabilities and applications of different parsers are compared.
A syntax‐correcting CIF parser, COD::CIF::Parser, is described that can parse CIF 1.1 files and accurately report the position and nature of the discovered syntactic problems while automatically correcting the most common and the most obvious syntactic deficiencies.
The Crystallography Open Database (COD), which is a project that aims to gather all available inorganic, metal–organic and small organic molecule structural data in one database, is described. The ...database adopts an open‐access model. The COD currently contains ∼80 000 entries in crystallographic information file format, with nearly full coverage of the International Union of Crystallography publications, and is growing in size and quality.
Published reports of chemical compounds often contain multiple machine-readable descriptions which may supplement each other in order to yield coherent and complete chemical representations. This ...publication presents a method to cross-check such descriptions using a canonical representation and isomorphism of molecular graphs. If immediate agreement between compound descriptions is not found, the algorithm derives the minimal set of simplifications required for both descriptions to arrive to a matching form (if any). The proposed algorithm is used to cross-check chemical descriptions from the Crystallography Open Database to identify coherently described entries as well as those requiring further curation.
Crystallography and Databases Bruno, Ian; Gra?ulis, Saulius; Helliwell, John R ...
Data science journal,
08/2017, Letnik:
16
Journal Article
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Crystallographic databases have existed as electronic resources for over 50 years, and have provided comprehensive archives of crystal structures of inorganic, organic, metal-organic and biological ...macromolecular compounds of immense value to a wide range of structural sciences. They thus serve a variety of scientific disciplines, but are all driven by considerations of accuracy, precise characterization, and potential for search, analysis and reuse. They also serve a variety of end-users in academia and industry, and have evolved through different funding and licensing models. The diversity of their operational mechanisms combined with their undisputed value as scientific research tools gives rise to a rich ecosystem. A session at SciDataCon2016 gave an overview of the largest extant crystallographic databases and their current activities and plans for the future. This review summarizes these presentations and considers them alongside other players in the field, demonstrating their variety, versatility and focus on quality and usefulness.
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