The effects of Leu or Val residues on cell selectivity of α-helical peptides.

In this study, the peptides were designed to compare the effect of multiple Leu or Val residues as the hydrophobic side of an α-helical model on their structure, function, and interaction with model membranes. The Leu-rich peptides displayed 4- to 16-fold stronger antimicrobial activity than Val-rich peptides, while Val-containing peptides showed no haemolysis and weak cytotoxicity. The peptides LR and VR showed an α-helical-rich structure under a membranemimicking environment. Different cell selectivity for Leu- or Val-containing peptides correlated with the targeted cell membranes. The Leu-rich peptide LR(W) and Val-rich peptide VR(W) interacted preferentially with negatively charged phospholipids over zwitterionic phospholipids. VR(W) displayed no interaction with zwitterionic phospholipids, which was consistent with its lack of haemolytic activity. The ability of LR to depolarize bacterial cells was much greater than that of VR. Val- and Leu-rich peptides appeared to kill bacteria in a membrane-targeted fashion, with different modes of action. Leu-rich peptides appeared to be active via a membrane-disrupting mode, while Val-rich peptides were active via the formation of small channels.