Conformations of twisted parallel beta-sheets and the origin of chirality in protein structures.

Abstract
An analysis of the conformational properties of parallel .beta.-pleated sheets suggests that an important factor in the generation of .beta.-sheet twist is the preference for nonplanar peptide bond distortions that impart local left-handed helical character to polypeptide chains. The introduction of such chiral distortions, which result from the tetrahedral deformation of the peptide N atoms, naturally produces right-twisted .beta.-sheet structures with optimal H-bond geometry.