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

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. It is demonstrated that the introduction of such chiral distortions, which result from the tetrahedral deformation of the peptide nitrogen atoms, naturally produces right-twisted beta-sheet structures with optimal hydrogen bond geometry.