Interactions of an antimicrobial peptide, magainin 2, with lipopolysaccharide-containing liposomes as a model for outer membranes of Gram-negative bacteria

F12W-magainin 2 preferentially interacted with lipopolysaccharide-containin g bilayers, permeabilizing the membranes, compared with lipopolysaccharide- free phosphatidylcholine vesicles. Using this system, we demonstrated for t he first time that the magainin peptide forms a helix upon binding to lipop olysaccharide. Incorporation of lipid A into phosphatidylcholine liposomes also enhanced interactions with the peptide. The presence of Mg2+, which nu llifies the peptide's antibacterial activity against Gram-negative bacteria , again weakened the interactions between the peptide and lipopolysaccharid e-doped bilayers, This system seems to be useful for investigating the mole cular details of peptide-lipopolysaccharide interactions. (C) 1999 Federati on of European Biochemical Societies.