Interaction of melittin with solid supported membranes

The interaction of the membrane active peptide melittin with solid supporte d lipid bilayers has been scrutinized by means of impedance spectroscopy an d scanning force microscopy. Highly flexible lipid bilayers anchored via a hydrophilic spacer terminated by a thiol group onto gold were used to inves tigate the influence of melittin on the electrical parameters of membranes by means of ac impedance analysis. A melittin induced increase in the capac itance and conductivity of the membrane was observed suggesting that melitt in induces defects within these immobilized lipid bilayers. Experiments wer e performed in the absence and presence of EDTA to investigate the influenc e of remaining phospholipase A(2) in the melittin sample as well as the sol e impact of phospholipase A(2) from Apis mellifera. It was shown that the m ost pronounced influence of melittin on the electrical parameters of bilaye rs was found when EDTA was absent, revealing a synergistic effect of phosph olipase A(2) and melittin. Morphological changes of solid supported membran es induced by the combined effect of melittin and phospholipase A(2) were v isualized by TappingMode scanning force microscopy in aqueous solution. Dis solution of the lipid layer and the formation of non-lamellar, discoid stru ctures was observed within minutes after addition of melittin, supporting a "carpet-like'' mechanism of peptide action leaving mixed peptide lipid mic elles behind. Scanning force microscopy allowed us to resolve the gradual a ction of melittin within one single scan.