Protein rotational diffusion measurements on the interaction of bee venom melittin with bacteriorhodopsin in lipid vesicles

The rotational diffusion of bacteriorhodopsin reconstituted into dimyristoylphosphatidylcholine vesicles was measured by the technique of flash-induced transient dichroism. In the presence of melittin, a cell lysing peptide from honey bee (Apis mellifera) venom, dose-dependent loss of rotational mobility was observed. Chemically modified melittin derivatives, in which free amine groups were either acetylated or succinylated, were impaired in their ability to induce immobilisation of bacteriorhodopsin. Bacteriorhodopsin reconstitutions of differing lipid/protein ratio were tested and it was found that the bacteriorhodopsin immobilisation phenomena depended on the melittin/protein ratio, not the melittin/lipid ratio. This suggests that melittin produces its effect via direct interaction with bacteriorhodopsin. A mechanism is proposed in which the aggregation of bacteriorhodopsin is induced by electrostatic attraction between its anionic surface moieties and the highly cationic C-terminal segment of melittin.