2001 Volume 130 Issue 3 Pages 393-397
Melittin-induced membrane fusion between neutral and acidic phospholipids was exam-ined in liposome systems with a high-sensitivity differential scanning calorimeter. Mem-brane fusion could be detected by calorimetric measurement by observing thermograms of mixed liposomal lipids. The roles of hydrophobic and electrostatic interactions were investigated in membrane fusion induced by melittin. Melittin, a bee venom peptide, is composed of a hydrophobic region including hydrophobic amino acids and a positively charged region including basic amino acids. When phosphatidylcholine liposomes were prepared in the presence of melittin, reductions in the phase transition enthalpies were observed in the following order; dimyristoylphosphatidylcholine (DMPC)>dipalmi-toylphosphatidylcholine (DPPC)>distearoylphosphatidylcholine (DSPC)>dielaidoyl-phosphatidylcholine (DEPC). The plase transition enthalpy of an acidic phospholipid, dipalmitoylphosphatidylserine (DPPS), was raised by melittin at low concentrations, then reduced at higher concentrations. DPPC liposomes prepared in melittin solution were fused with DPPS liposomes when the liposomal dispersions were mixed and incu-bated. Similar fusion was observed between dipalmitoylphosphatidylcholine and di-myristoylphosphatidic acid (DMPA) liposomes. These results indicate that a peptide in-cluding hydrophobic and basic regions can mediate membrane fusion between neutral and acidic liposomes by hydrophobic and electrostatic interactions.
