Structure-function relationship of model Aib-containing peptides as ion transfer intermembrane templates

Peptaibols comprise a family of peptide antibiotics with high contents of a -aminoisobutyric acid (Aib) residues and C-terminal amino alcohols. These p eptides form a-helical structures leading to voltage-gated ion channels in lipid membranes. In the present study, amphiphilic helical Aib-containing p eptides of various chain-lengths, Ac-(Aib-Lys-Aib-Ala)(n)-NH2 (n = 1-5), we re designed to investigate the mechanisms of the aggregation and transmembr ane orientation of helical motifs in lipid bilayer membranes. Peptide synth esis was performed by the conventional stepwise Fmoc solid-phase method. Th e crude peptides were obtained in high yields (66-85%) with high purities ( 69-95%), Conformational analysis of the synthetic peptides was performed by CD spectroscopy. It was found that these peptides take on highly helical s tructures, and the helicity of the peptides increases with an increase in c hain-length. The longest peptide, Ac-(Aib-Lys-Aib-Ala)(5)-NH2, self-aggrega tes and adopts a barrel-stave conformation in liposomes, Ac-(Aib-Lys-Aib-Al a)(5)-NH2 exhibited potent antimicrobial activity against Gram-positive bac teria. Patch-clamp measurements revealed that this peptide can form well-de fined ion channels with a long lifetime at relatively low transbilayer pote ntials and peptide concentrations. For this peptide, the single-channel con ductance of the most frequent event is 227 pS, which could be related to a single-state tetrameric pore.