Fusogenic virosomes prepared by partitioning of vesicular stomatitis virus G protein into preformed vesicles.

Virosomes were prepared by the insertion of vesicular stomatitis virus glycoprotein, a pH-sensitive fusion protein, into preformed liposomes. The fusogenic activity of these virosomes was characterized in cell-free fusion assays using liposomal targets. Fusion was monitored by concentration-dependent changes in the efficiency of resonance energy transfer between N-(lissamine rhodamine B sulfonyl)-phosphatidylethanolamine and N-(4-nitrobenzo-2-oxa-1,3-diazol)-phosphatidylethanolamine and by electron microscopy. The fusogenic activity was dependent on the presence of vesicular stomatitis virus glycoprotein, was pH-sensitive, and had a pH threshold of activation similar to that of the native virus. The extent of fusion was dependent upon the lipid composition of the vesicles. This technique will allow vesicles prepared by any method to be made fusogenic.