Long Polypeptide 310-helices at Atomic Resolution

• Published in: Proceedings of the National Academy of Sciences - PNAS 1986-04, Vol.83 (7), p.1988-1992
• Main Authors: Bavoso, Alfonso, Benedetti, Ettore, Di Blasio, Benedetto, Pavone, Vincenzo, Pedone, Carlo, Toniolo, Claudio, Bonora, Gian Maria
• Format: Article
• Language: English
• Subjects: Amino acids; Aminoisobutyric acids; Antibiotics; Atoms; Biochemistry; Biological and medical sciences; Biological Sciences: Biochemistry; Biopolymers; Crystal structure; Crystalline structure; Fundamental and applied biological sciences. Psychology; Hydrogen bonds; Molecular biophysics; Molecules; Structure in molecular biology; X ray diffraction
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.83.7.1988

The crystal-state preferred conformation of the terminally blocked homooctapeptide from the Cα,α-dimetylated α -aminoisobutyric acid (Aib) residue, pBrBz- (Aib)8-OBut, in which pBrBz is para-bromobenzoyl and OBut is tert-butoxy, determined by x-ray diffraction analysis using direct methods, was found to be a 310-helix stabilized by six consecutive intramolecular N--H...O==C hydrogen bonds of the C10-III (or III′) type. This is the first observation at atomic resolution of a regular 310-helix longer than two complete turns. The solid-state structural analysis was extended to the terminally blocked, α -aminoisobutyric acid-rich octapeptide corresponding to the 2-9 sequence of the peptaibol antibiotics emerimicins III and IV, pBrBz-Aib3-L-Val-Gly-L-Leu-Aib2-OMe . Again, this peptide adopts a (right-handed) 310-helical structure, although slightly distorted at the level of the L-leucine residue. The role of specific amino acid sequence and peptide main-chain length in stabilizing either the 310- or the α -helical conformation and their possible implications on the nature of the channel formed by peptaibol antibiotics in the membrane are also briefly discussed.