Formation of membrane domains by the envelope proteins of vesicular stomatitis virus

The properties of the two envelope-associated proteins of vesicular stomatitis virus, the glycoprotein (G) and the matrix protein (M), were investigated in order to understand the mechanism of virus budding and domain formation in membranes. Fluorescence resonance energy transfer was used to study the interaction between the G protein and specific phospholipids. The protein had the highest affinity for phosphatidic acid among the phospholipids tested. Fluorescence digital imaging microscopy also was used to determine how the protein could alter the lateral distribution of phospholipids in membranes. Large domains enriched in phosphatidic acid were observed when the protein was incorporated into phospholipid vesicles. The G protein colocalized with the phosphatidic acid-enriched domains. Similar experiments carried out with the M protein showed that the M protein induced the formation of domains enriched not only in phosphatidic acid but also in phosphatidylserine. The phosphatidic acid-enriched domains induced by either the G or M proteins were similar in terms of the degree of enrichment of phosphatidic acid and the size of the domains. When the two proteins were reconstituted in vesicles at the same time, the domains were condensed. There was a greater degree of phosphatidic acid enrichment, and the size of the domains was reduced. The formation of domains enriched in the viral proteins and specific phospholipids may mimic the first steps that occur during budding of the virus from the plasma membrane of infected cells.