Effects of incorporation of various amphiphiles into recipient liposome membranes on inter-membrane protein transfer.

To obtain information about the factors governing spontaneous inter-membrane protein transfer, we examined the effects of incorporation of various amphiphilic compounds in dimyristoylphosphatidylcholine (DMPC) liposomes on protein transfer from influenza virus-infected cells to the liposomes, and analyzed the physical properties of these liposome membranes. The incorporation of amphiphilic compounds, negatively charged dicetylphosphate (DCP), dipalmitoylphosphatidylserine (DPPS) or positively charged dimethyldipalmitoylammonium (DMDPA), into DMPC liposomal membranes enhanced protein transfer. The liposomes containing DCP, DPPS or DMDPA were unaffected by osmotic shock caused by external addition of glucose, suggesting a decrease in lipid packing in the liposomal membranes. Furthermore, calorimetric study of these liposomes showed that a phase separation occurred partially in the liposomal membranes. Accordingly, the membranes of DMPC liposomes containing DCP, DPPS and DMDPA should be distorted due to the coexistence of two phases, gel and liquid crystalline, in the membranes. Consequently, the membrane distortion could be responsible for the enhancement effects of the amphiphiles on the inter-membrane protein transfer from influenza virus-infected cells to the liposomes.