Selective interaction of synthetic antimicrobial peptides derived from sapecin B with lipid bilayers.

By measuring carboxyfluorescein leakage from liposomes and the increase in membrane current through planar lipid bilayer membranes, we examined the capacities of a series of low-molecular-weight cationic amphiphilic peptides derived from the alpha-helix domain of sapecin B for membrane-perturbation and ion-channel formation. Some of these peptides strongly interact with membranes containing acidic phospholipids and phosphatidylethanolamine, with a very negative potential, which are characteristic of the Escherichia coli membrane, in parallel with their antimicrobial activity. In contrast, they do not interact with membranes which predominantly contain choline phospholipids and cholesterol in their outer leaflets, with a slightly negative potential, all of which are characteristic of eukaryotic membranes, thereby providing a molecular basis for their selective toxicity. Membranes doped with these peptides are as permeable to inorganic phosphates as to chloride ions and are far more permeable to cations. The loss of inorganic phosphates may damage bacterial cells due to rapid depletion of cytoplasmic ATP. Examination of the structure-activity relationships of a series of derived peptides in their interaction with a model of the E. coli membrane confirmed the necessity of cationic amphiphilicity for the peptides to attack the bacterial membrane and to exhibit antimicrobial activity.