The interactions of histidine-containing amphipathic helical peptide antibiotics with lipid bilayers. The effects of charges and pH

Abstract

The α-helix of the designed amphipathic peptide antibiotic LAH4 (KKALLALALHHLAHLALHLALAHKKANH2) 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). LAH4 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 LAH4 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 LAH4 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 LAH4 is significantly decreased for negatively charged membranes. Pronounced differences in the interactions of LAH4 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.