Long, Chiral Polypeptide-310- Helices At Atomic Resolution

The crystal-state preferred conformation of the terminally blocked hepta- and octapeptides with the general formula -(Aib)n L-Leu-(Aib)2- (n=4 and 5, respectively), determined by X- ray diffraction, was found to be a right-handed 310-helix stabilized by five and six consecutive intramolecular NH   0=C H-bonds of the C10-III type, respectively. The octapeptide structure represents the first observation at atomic resolution of a regular, chiral 310-helix larger than two complete turns. In both cases the right handed screw sense of the helix is dictated by the presence of the single, internal L-residue. This study confirms the propensity of short peptides rich in Aib, the prototype of the amino acid residues dialkylated at the α carbon, to adopt a 310- helical structure and is expected to help our understanding of the conformational preferences of the membrane-active, channel-forming, ion-transporting peptaibol antibiotics. © Taylor & Francis Group, LLC.