Geometrical validation around the Calpha is described, with a new Cbeta measure and updated Ramachandran plot. Deviation of the observed Cbeta atom from ideal position provides a single measure encapsulating the major structure-validation information contained in bond angle distortions. Cbeta deviation is sensitive to incompatibilities between sidechain and backbone caused by misfit conformations or inappropriate refinement restraints. A new phi,psi plot using density-dependent smoothing for 81,234 non-Gly, non-Pro, and non-prePro residues with B < 30 from 500 high-resolution proteins shows sharp boundaries at critical edges and clear delineation between large empty areas and regions that are allowed but disfavored. One such region is the gamma-turn conformation near +75 degrees,-60 degrees, counted as forbidden by common structure-validation programs; however, it occurs in well-ordered parts of good structures, it is overrepresented near functional sites, and strain is partly compensated by the gamma-turn H-bond. Favored and allowed phi,psi regions are also defined for Pro, pre-Pro, and Gly (important because Gly phi,psi angles are more permissive but less accurately determined). Details of these accurate empirical distributions are poorly predicted by previous theoretical calculations, including a region left of alpha-helix, which rates as favorable in energy yet rarely occurs. A proposed factor explaining this discrepancy is that crowding of the two-peptide NHs permits donating only a single H-bond. New calculations by Hu et al. [Proteins 2002 (this issue)] for Ala and Gly dipeptides, using mixed quantum mechanics and molecular mechanics, fit our nonrepetitive data in excellent detail. To run our geometrical evaluations on a user-uploaded file, see MOLPROBITY (http://kinemage.biochem.duke.edu) or RAMPAGE (http://www-cryst.bioc.cam.ac.uk/rampage).

No abstract

All published rotamer libraries contain some rotamers that exhibit impossible internal atomic overlaps if built in ideal geometry with all hydrogen atoms. Removal of uncertain residues (mainly those with B‐factors ≥40 or van der Waals overlaps ≥0.4 Å) greatly improves the clustering of rotamer populations. Asn, Gln, or His side chains additionally benefit from flipping of their planar terminal groups when required by atomic overlaps or H‐bonding. Sensitivity to skew and to the boundaries of χ angle bins is avoided by using modes rather than traditional mean values. Rotamer definitions are listed both as the modal values and in a preferred version that maximizes common atoms between related rotamers. The resulting library shows significant differences from previous ones, differences validated by considering the likelihood of systematic misfitting of models to electron density maps and by plotting changes in rotamer frequency with B‐factor. Few rotamers now show atomic overlaps in ideal geometry; those overlaps are relatively small and can be understood in terms of bond angle distortions compensated by favorable interactions. The new library covers 94.5% of examples in the highest quality protein data with 153 rotamers and can make a significant contribution to improving the accuracy of new structures. Proteins 2000;40:389–408. © 2000 Wiley‐Liss, Inc.

All published rotamer libraries contain some rotamers that exhibit impossible internal atomic overlaps if built in ideal geometry with all hydrogen atoms. Removal of uncertain residues (mainly those with B-factors >/=40 or van der Waals overlaps >/=0.4 A) greatly improves the clustering of rotamer populations. Asn, Gln, or His side chains additionally benefit from flipping of their planar terminal groups when required by atomic overlaps or H-bonding. Sensitivity to skew and to the boundaries of chi angle bins is avoided by using modes rather than traditional mean values. Rotamer definitions are listed both as the modal values and in a preferred version that maximizes common atoms between related rotamers. The resulting library shows significant differences from previous ones, differences validated by considering the likelihood of systematic misfitting of models to electron density maps and by plotting changes in rotamer frequency with B-factor. Few rotamers now show atomic overlaps in ideal geometry; those overlaps are relatively small and can be understood in terms of bond angle distortions compensated by favorable interactions. The new library covers 94.5% of examples in the highest quality protein data with 153 rotamers and can make a significant contribution to improving the accuracy of new structures. Proteins 2000;40:389-408.

The pKa-cooperative aims to provide a forum for experimental and theoretical researchers interested in protein pKa values and protein electrostatics in general. The first round of the pKa-cooperative, which challenged computational labs to carry out blind predictions against pKas experimentally determined in the laboratory of Bertrand Garcia-Moreno, was completed and results discussed at the Telluride meeting (July 6–10, 2009). This paper serves as an introduction to the reports submitted by the blind prediction participants that will be published in a special issue of PROTEINS: Structure, Function and Bioinformatics. Here we briefly outline existing approaches for pKa calculations, emphasizing methods that were used by the participants in calculating the blind pKa values in the first round of the cooperative. We then point out some of the difficulties encountered by the participating groups in making their blind predictions, and finally try to provide some insights for future developments aimed at improving the accuracy of pKa calculations.