Long polypeptide 3(10)-helices at atomic resolution.
The crystal-state preferred conformation of the terminally blocked homooctapeptide from the C(alpha,alpha)-dimethylated alpha-aminoisobutyric acid (Aib) residue, pBrBz-(Aib)(8)-OBu(t), in which pBrBz is para-bromobenzoyl and OBu(t) is tert-butoxy, determined by x-ray diffraction analysis using direct methods, was found to be a 3(10)-helix stabilized by six consecutive intramolecular N-H....O=C hydrogen bonds of the C(10)-III (or III') type. This is the first observation at atomic resolution of a regular 3(10)-helix longer than two complete turns. The solid-state structural analysis was extended to the terminally blocked, alpha-aminoisobutyric acid-rich octapeptide corresponding to the 2-9 sequence of the peptaibol antibiotics emerimicins III and IV, pBrBz-Aib(3)-L-Val-Gly-L-Leu-Aib(2)-OMe. Again, this peptide adopts a (right-handed) 3(10)-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 3(10)- or the alpha-helical conformation and their possible implications on the nature of the channel formed by peptaibol antibiotics in the membrane are also briefly discussed.
Dipartimento di Chimica, University of Napoli, Napoli, Italy.
A
A
Bavoso
E
E
Benedetti
B
B
Di Blasio
V
V
Pavone
C
C
Pedone
C
C
Toniolo
G M
GM
Bonora