The Interactions of Histidine-containing Amphipathic Helical Peptide Antibiotics with Lipid Bilayers: THE EFFECTS OF CHARGES AND pH

Abstract

The alpha-helix of the designed amphipathic peptide antibiotic LAH(4 )(KKALLALALHHLAHLALHLALALKKA-NH(2)) strongly interacts with phospholipid membranes. The peptide is oriented parallel to the membrane surface under acidic conditions, but transmembrane at physiological pH (Bechinger, B. (1996) J. Mol. Biol. 263, 768-775). LAH(4) exhibits antibiotic activities against Escherichia coli and Bacillus subtilis; the peptide does not, however, lyse human red blood cells at bacteriocidal concentrations. The antibiotic activities of LAH(4) are 2 orders of magnitude more pronounced at pH 5 when compared with pH 7.5. Although peptide association at low pH is reduced when compared with pH 7.5, the release of the fluorophore calcein from large unilamellar 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol vesicles is more pronounced at pH values where LAH(4) adopts an orientation along the membrane surface. The calcein release experiments thereby parallel the results obtained in antibiotic assays. Despite a much higher degree of association, calcein release activity of LAH(4) is significantly decreased for negatively charged membranes. Pronounced differences in the interactions of LAH(4) with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol or 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine membranes also become apparent when the mechanisms of dye release are investigated. The results presented in this paper support models in which antibiotic activity is caused by detergent-like membrane destabilization, rather than pore formation by helical peptides in transmembrane alignments.