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

Peptaibols comprise a family of peptide antibiotics with high contents of 2-aminoisobutyric acid (Aib) residues and C-terminal amino alcohols. These peptides form alpha-helical structures leading to voltage-gated ion channels in lipid membranes. In the present study, amphiphilic helical Aib-containing peptides of various chain-lengths, Ac-(Aib-Lys-Aib-Ala)n-NH2 (n = 1-5), were designed to investigate the mechanisms of the aggregation and transmembrane orientation of helical motifs in lipid bilayer membranes. Peptide synthesis was performed by the conventional stepwise Fmoc solid-phase method. The 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 structures, and the helicity of the peptides increases with an increase in chain-length. The longest peptide, Ac-(Aib-Lys-Aib-Ala)5-NH2, self-aggregates and adopts a barrel-stave conformation in liposomes. Ac-(Aib-Lys-Aib-Ala)5-NH2 exhibited potent antimicrobial activity against Gram-positive bacteria. Patch-clamp measurements revealed that this peptide can form well-defined ion channels with a long lifetime at relatively low transbilayer potentials and peptide concentrations. For this peptide, the single-channel conductance of the most frequent event is 227 pS, which could be related to a single-state tetrameric pore.