Membrane fusion between liposomes composed of acidic phospholipids and neutral phospholipids induced by melittin: A differential scanning calorimetric study

Melittin-induced membrane fusion between neutral and acidic phospholipids w as examined in liposome systems with a high-sensitivity differential scanni ng calorimeter. Membrane fusion could be detected by calorimetric measureme nt by observing thermograms of mixed liposomal lipids. The roles of hydroph obic and electrostatic interactions were investigated in membrane fusion in duced by melittin. Melittin, a bee venom peptide, is composed of a hydropho bic region including hydrophobic amino acids and a positively charged regio n including basic amino acids. When phosphatidylcholine liposomes were prep ared in the presence of melittin, reductions in the phase transition enthal pies were observed in the following order; dimyristoylphosphatidylcholine ( DMPC) > dipalmitoylphosphatidylcholine (DPPC) > distearoylphosphatidylcholi ne (DSPC) > dielaidoylphosphatidylcholine (DEPC). The plase transition enth alpy of an acidic phospholipid, dipalmitoylphosphatidylserine (DPPS), was r aised by melittin at low concentrations, then reduced at higher concentrati ons. DPPC liposomes prepared in melittin solution were fused with DPPS lipo somes when the liposomal dispersions were mixed and incubated. Similar fusi on was observed between dipalmitoylphosphatidylcholine and dimyristoylphosp hatidic acid (DMPA) liposomes. These results indicate that a peptide includ ing hydrophobic and basic regions can mediate membrane fusion between neutr al and acidic liposomes by hydrophobic and electrostatic interactions.