A proline-rich motif within the matrix protein of vesicular stomatitis virus and rabies virus interacts with WW domains of cellular proteins: Implications for viral budding

The matrix (M) protein of rhabdoviruses has been shown to play a key role i n virus assembly and budding; however, the precise mechanism by which M med iates these processes remains unclear. We have associated a highly conserve d, proline-rich motif (PPxY or PY motif, where P denotes proline, Y represe nts tyrosine, and x denotes any amino acid) of rhabdoviral M proteins with a possible role in budding mediated by the M protein. Point mutations that disrupt the PY motif of the M protein of vesicular stomatitis virus (VSV) h ave no obvious effect on membrane localization of M but instead lead to a d ecrease in the amount of M protein released from cells in a functional budd ing assay. Interestingly, the PPxY sequence within rhabdoviral M proteins i s identical to that of the ligand which interacts with WW domains of cellul ar proteins. Indeed, results from two in vitro binding assays demonstrate t hat amino acids 17 through 33 anti 29 through 44, which contain the PY moti fs of VSV and rabies virus M proteins, respectively, mediate interactions w ith WW domains of specific cellular proteins. Point mutations that disrupt the consensus PY motif of VSV or rabies virus M protein result in a signifi cant decrease in their ability to interact with the WW domains. These prope rties of the PY motif of rhabdovirus M proteins are strikingly analogous te a those of the late (L) budding domain identified in the gag-specific prote in p2b of Rous sarcoma virus. Thus, it is possible that rhabdoviruses may u surp host proteins to facilitate the budding process and that late stages i n the budding process of rhabdoviruses and retroviruses may have features i n common.