Ebola virus VP40-induced particle formation and association with the lipidbilayer

Viral protein 40 (VP40) of Ebola virus appears equivalent to matrix protein s of other viruses, yet little is known about its role in the viral life cy cle. To elucidate the functions of VP40, we investigated its ability to ind uce the formation of membrane-bound particles when it was expressed apart f rom other viral proteins. We found that VP40 is indeed able to induce parti cle formation when it is expressed in mammalian cells, and this process app eared to rely on a conserved N-terminal PPXY motif, as mutation or loss of this motif resulted in markedly reduced particle formation, These findings demonstrate that VP40 alone possesses the information necessary to induce p article formation, and this process most likely requires cellular WW domain -containing proteins that interact with the PPXY motif of VP40. The ability of VP40 to bind cellular membranes was also studied. Flotation gradient an alysis indicated that VP40 binds to membranes in a hydrophobic manner, as N aCl at 1 M did not release the protein from the lipid bilayer, Triton X-114 phase-partitioning analysis suggested that VP40 possesses only minor featu res of an integral membrane protein. We confirmed previous findings that tr uncation of the 50 C-terminal amino acids of VP40 results in decreased asso ciation with cellular membranes and demonstrated that this deletion disrupt s hydrophobic interactions of VP40 with the lipid bilayer, as well as aboli shing particle formation. Truncation of the 150 C-terminal amino acids or 1 00 N-terminal amino acids of VP40 enhanced the protein's hydrophobic associ ation with cellular membranes, These data suggest that VP40 binds the lipid bilayer in an efficient yet structurally complex fashion.