FORMATION OF MEMBRANE DOMAINS CREATED DURING THE BUDDING OF VESICULARSTOMATITIS-VIRUS - A MODEL FOR SELECTIVE LIPID AND PROTEIN SORTING INBIOLOGICAL-MEMBRANES

Vesicular stomatitis virus buds from domains of the plasma membrane th at have a unique protein and lipid composition. Fluorescence digital i maging microscopy and resonance energy transfer were used to determine how the two viral envelope-associated proteins, the G and the M prote ins, could alter the lateral distribution of lipids in large unilamell ar vesicles and form domains. The G protein formed large domains in ve sicles containing phosphatidic acid but not with phosphatidylserine, w hile the M protein formed domains enriched in both acidic phospholipid s. Domains enriched in sphingomyelin were observed only when both the G protein and the M protein were present in vesicles containing phosph atidic acid. Phosphatidylcholine and gramicidin (chosen to represent a host membrane protein) were excluded from the domains. Cholesterol wa s induced to partition into the domains only in vesicles containing ph osphatidic acid and sphingomyelin along with both of the proteins. Pho sphatidylethanolamine was not enriched or depleted in the domains. Dom ains of similar composition were formed using vesicles made from diole ylphospholipids and the lipids extracted from BHK-21 plasma membranes, indicating that the fatty acid composition was not as important as th e polar head groups of the phospholipids, The phospholipid and cholest erol compositions of the domains formed by the G and the M proteins in vesicles were very similar to the composition of the viral envelope, suggesting that the domains represent the areas in the plasma membrane where the virus buds. This study provides a model for selective lipid and protein sorting that occurs in biological membranes.