Glycine rescue of β-sheets from cis-proline.

Proline is incompatible with ideal β-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 β-sheets and rescues the β-sheet from severe distortions by assuming a right-handed polyproline conformation (β(PR)), effectively increasing the local β-sheet register by one residue. The united residue, Gly(β(PR))-cisPro, is evolutionarily conserved, functionally important, and dynamic in nature.