Geometrical criteria for left-handed twists within protein beta-strands

Using a statistical analysis on beta-sheet structures from the Protein Data Bank, characteristic angles within beta-strands were correlated to the nature of the side chains. The twists were computed from the atomic coordinates of five consecutive amino acids’ alpha carbons from single beta-strand sequences. Conditions on the angles for twists to be mainly left-handed are given together with the frequency of occurrence for these non-standard geometrical properties within protein beta-strands. Applications in protein structure prediction and CASP challenges in particular are envisioned by making use of the probabilities of occurrence in protein structures of angle value ranges for given amino acids.