Interaction of melittin with solid supported membranes

Abstract

The interaction of the membrane active peptide melittin with solid supported lipid bilayers has been scrutinized by means of impedance spectroscopy and scanning force microscopy. Highly flexible lipid bilayers anchored via a hydrophilic spacer terminated by a thiol group onto gold were used to investigate the influence of melittin on the electrical parameters of membranes by means of ac impedance analysis. A melittin induced increase in the capacitance and conductivity of the membrane was observed suggesting that melittin induces defects within these immobilized lipid bilayers. Experiments were performed in the absence and presence of EDTA to investigate the influence of remaining phospholipase A(2) in the melittin sample as well as the sole impact of phospholipase A(2) from Apis mellifera. It was shown that the most pronounced influence of melittin on the electrical parameters of bilayers was found when EDTA was absent, revealing a synergistic effect of phospholipase A(2) and melittin. Morphological changes of solid supported membranes induced by the combined effect of melittin and phospholipase A(2) were visualized by TappingMode scanning force microscopy in aqueous solution. Dissolution of the lipid layer and the formation of non-lamellar, discoid structures was observed within minutes after addition of melittin, supporting a "carpet-like' mechanism of peptide action leaving mixed peptide lipid micelles behind. Scanning force microscopy allowed us to resolve the gradual action of melittin within one single scan.