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R W Hooft

Publications and source records attributed to R W Hooft.

7 recordsLinked to original sources
PubMed1997

Objectively judging the quality of a protein structure from a Ramachandran plot.

MOTIVATION: Statistical methods that compare observed and expected distributions of experimental observables provide powerful tools for the quality control of protein structures. The distribution of backbone dihedral angles ('Ramachandran plot') has often been used for such quality control, but without a firm statistical foundation. RESULTS: A new and-simple method is presented for judging the quality of a protein structure based on the distribution of backbone dihedral angles. Inputs to the method are 60 torsion angle distributions extracted from protein structures solved at high resolution; one for each combination of residue type and tri-state secondary structure. Output for a protein is a Ramachandran Z-score, expressing the quality of the Ramachandran plot relative to current state-of-the-art structures.

Algorithms↗
PubMed1996

Positioning hydrogen atoms by optimizing hydrogen-bond networks in protein structures.

A method is presented that positions polar hydrogen atoms in protein structures by optimizing the total hydrogen bond energy. For this goal, an empirical hydrogen bond force field was derived from small molecule crystal structures. Bifurcated hydrogen bonds are taken into account. The procedure also predicts ionization states of His, Asp, and Glu residues. During optimization, side-chain conformations of His, Gln, and Asn residues are allowed to change their last chi angle by 180 degrees to compensate for crystallographic misassignments. Crystal structure symmetry is taken into account where appropriate. The results can have significant implications for molecular dynamics simulations, protein engineering, and docking studies. The largest impact, however, is in protein structure verification: over 85% of protein structures tested can be improved by using our procedure.

Amino Acids↗
PubMed1996

PRODRG, a program for generating molecular topologies and unique molecular descriptors from coordinates of small molecules.

A software package is described that operates on small molecules observed in the PDB collection of protein structures. Molecular topology files for many molecular modeling programs can be generated automatically. The three-dimensional coordinates of small molecules can be converted to molecular descriptor strings that encode them uniquely in order to enable small-molecule recognition, despite high variability in atom and molecule nomenclature. From this descriptor a plausible 3D structure can be regenerated using energy minimisation. Alternatively, an ensemble of structures can be generated using a distance-geometry-based algorithm.

Ligands↗
PubMed1996

Improved coordinate reconstruction from stereo diagrams.

A program has been written that reconstructs three-dimensional coordinates for a protein structure given a stereo C alpha diagram. Initial three-dimensional coordinates are determined using an algorithm similar to the one used by Rossmann in the program STEREO. Thereafter the coordinates are refined such that the stereo image based on the reconstructed three-dimensional coordinates optimally fits the scanned stereo image while normal C alpha stereochemistry is enforced.

Computer Communication Networks↗
PubMed1996

The PDBFINDER database: a summary of PDB, DSSP and HSSP information with added value.

MOTIVATION: The Protein Data Bank currently contains more than 4700 protein coordinate sets. It is often desirable to make a selection from these files based on a criterion like R-factor, experimental method, length of the amino acid sequence, or the number of homologous sequences in SWISSPROT. Doing this using the distributed form of the Protein Data Bank can be a tedious task, because (1) this requires reading one file for every single entry, and (2) not all of the information is present in a consistent computer readable way in all of the entries. RESULTS: The PDBFINDER database provides an easy to interpret file containing summary information about all Protein Data Bank files. Summary information from the DSSP (Definition of Secondary Structure of Proteins) and HSSP (Homology derived Secondary Structure of Proteins) databases is also included. Furthermore, where essential data were missing from the Protein Data Bank file, this information has been retrieved from the original literature. AVAILABILITY: The latest version of the PDBFINDER database can be downloaded by anonymous ftp from swift.embl-heidelberg.de, directory:/pdbfinder. CONTACT: E-mail address hooft@embl-heidelberg.de.

Amino Acid Sequence↗
PubMed1995

The use of position-specific rotamers in model building by homology.

In this study we concentrate on replacing side chains as a subtask of model building by homology. Two problems arise. How to determine potential low energy rotamers? And how to avoid the combinatorial explosion that results from the combination of many residues for which multiple good rotamers are predicted? We attempt to solve these problems by choosing position-specific rather than generalized rotamers and by sorting the residues that have to be modelled as a function of their freedom in rotamer space. The practical advantages of our method are the quality of the models for cases of high backbone similarity, the small amount of human intervention needed, and the fact that the method automatically estimates the reliability with which each residue has been modeled. Other methods described in this issue are probably more suitable if large backbone rearrangements or loop insertions and deletions need to be modeled.

Bacterial Proteins↗