Glycine rescue of β-sheets from cis-proline.

Proline is incompatible with ideal beta-sheet geometry, and the incompatibility gets magnified when Pro assumes the cis peptidyl-prolyl conformation. We show that Gly appears with high propensity at pre-cisPro positions in beta-sheets and rescues the beta-sheet from severe distortions by assuming a right-handed polyproline conformation (beta(PR)), effectively increasing the local beta-sheet register by one residue. The united residue, Gly(beta(PR))-cisPro, is evolutionarily conserved, functionally important, and dynamic in nature.