The fusion protein of Peste des petits ruminants virus mediates biological fusion in the absence of hemagglutinin-neuraminidase protein.

To study the process of membrane fusion in Morbilliviruses, the fusion (F) glycoproteins of Peste des petits ruminants virus (PPRV) and Rinderpest virus (RPV) were expressed transiently in mammalian cells. The recombinant F proteins were found to be localized at the surface of transfected cells. The fusion activity, as evident from cell fusion assays and lysis of chicken erythrocytes, documented that transiently expressed PPRV F glycoprotein induces cell fusion in the absence of homotypic hemagglutinin-neuraminidase (HN) attachment glycoprotein. The coexpression of homotypic HN increased the extent of fusion by twofold, while the efficiency of fusion was found to be substantially enhanced. In contrast, in RPV F-expressing cells, fusion was detected only when homotypic hemagglutinin (H) or heterotypic HN protein was coexpressed. This differs from the strict type-specific requirement for the attachment protein as in the fusion process of most of the paramyxoviruses. Further, we demonstrate by fluorescence transfer experiments that while PPRV F brings about both hemifusion and complete fusion on its own, RPV F induces only hemifusion while it brings about complete fusion in the presence of homotypic or heterotypic attachment protein.