Phenotypes of vesicular stomatitis virus mutants with mutations in the PSAP motif of the matrix protein
Linda Obiang, Hélène Raux, Malika Ouldali, Danielle Blondel and Yves Gaudin
Vesicular stomatitis virus (VSV) matrix protein (M) has a flexible amino-terminal part that recruits cellular partners. It contains a dynamin binding site, that is required for efficient viral assembly, and two motifs, 24PPPY27 and 37PSAP40, that constitute potential late domains. Late domains are present in proteins of several enveloped viruses and are involved in the ultimate step of the budding process (i.e. fission between viral and cellular membranes). In BHK21 cells, it has been demonstrated that the 24PPPY27 motif binds the Nedd4 E3 ubiquitine ligase for efficient viral budding and that the 37PSAP40 motif, although conserved among vesiculoviruses M proteins, does not possess L-domain activity. In this study, we have reexamined the contribution of the PSAP motif to VSV budding. First, we demonstrate that VSV M indeed binds TSG101 (a component of the ESCRT1 complex) through its PSAP motif. Second, we analyzed the phenotype of several recombinant mutants. We show that a double mutant with point mutations in both the PSAP and the PPPY motifs is impaired compared to a single mutant in the PPPY motif indicating that the PSAP motif partially compensates the lack of PPPY motif. Mutants phenotype depend on cell lines: in CERA cells, a recombinant virus with a single mutation in the PSAP motif is impaired compared to wild type and a mutant with a single mutation in the dynamin binding motif was much less impaired in Vero cells than in BSR cells. These results have implications on VSV budding pathway that will be discussed.