C11/C9 helices in crystals of αβ hybrid peptides and switching structures between helix types by variation in the α-residue

Abstract

Close-packed helices with mixed hydrogen bond directionality are unprecedented in the structural chemistry of α-polypeptides. While NMR studies in solution state provide strong evidence for the occurrence of mixed helices in (ββ)n and (αβ)n sequences, limited information is currently available in crystals. The peptide structures presented show the occurrence of C11/C9 helices in (αβ)n peptides. Transitions between C11 and C11/C9 helices are observed upon varying the α-amino acid residue.