Membrane selectivity by W-tagging of antimicrobial peptides

A pronounced membrane selectivity is demonstrated for short, hydrophilic, and highly charged antimicrobial peptides, end-tagged with aromatic amino acid stretches. The mechanisms underlying this were investigated by a method combination of fluorescence and CD spectroscopy, ellipsometry, and Langmuir balance measurements, as well as with functional assays on cell toxicity and antimicrobial effects. End-tagging with oligotryptophan promotes peptide-induced lysis of phospholipid liposomes, as well as membrane rupture and killing of bacteria and fungi. This antimicrobial potency is accompanied by limited toxicity for human epithelial cells and low hemolysis. The functional selectivity displayed correlates to a pronounced selectivity of such peptides for anionic lipid membranes, combined with a markedly reduced membrane activity in the presence of cholesterol. As exemplified for GRR10W4N (GRRPRPRPRPWWWW-NH(2)), potent liposome rupture occurs for anionic lipid systems (dioleoylphosphatidylethanolamine (DOPE)/dioleoylphosphatidylglycerol (DOPG) and Escherichia coli lipid extract) while that of zwitterionic dioleoylphosphatidylcholine (DOPC)/cholesterol is largely absent under the conditions investigated. This pronounced membrane selectivity is due to both a lower peptide binding to the zwitterionic membranes (z≈-8-10mV) than to the anionic ones (z≈-35-40mV), and a lower degree of membrane incorporation in the zwitterionic membranes, particularly in the presence of cholesterol. Replacing cholesterol with ergosterol, thus mimicking fungal membranes, results in an increased sensitivity for peptide-induced lysis, in analogy to the antifungal properties of such peptides. Finally, the generality of the high membrane selectivity for other peptides of this type is demonstrated.