Electric charges of the lipid headgroup modulate Melittin adsorption to lipid vesicle membranes

Abstract

Peptide lipid membrane interactions are modulated by factors such as peptide hydrophobicity and the electric charge of both the peptide and the membrane surface. We investigated the influence of lipid headgroup charge on the adsorption of Melittin (Mel) on the surface of artificial lipid vesicles in conditions that mimic the interaction with biological cells, such as ionic strength, pH, and peptide concentration. Taking advantage of Mel TRP residue fluorescence, we used several fluorescence techniques (FRET, fluorescence quenching, time-resolved fluorescence) to investigate Mel adsorption on the surface of the DMPC and DMPC with fractions of positively charged lipids (EPC) or negatively charged lipids (DPPG) vesicles. Our results show that the DMPC:DPPG vesicles allow a deeper localization of TRP residues in the lipid membrane, proven by the blue shift of the TRP emission spectrum and the exclusion radius evaluated from FRET. We also showed that even for positively charged surfaces Mel tends to adsorb on the lipid surface. The results were confirmed indirectly by quencher accessibility to TRP. Finally, we discuss the results in correlation to the Mel effects on biological cells