The Importance of Conformational Mobility to the Post-Attachment Functions of Reovirus σ1 Attachment Protein
Mammalian orthoreovirus (reovirus) is a member of the reoviridae virus family of segmented, double-stranded (ds) RNA genomes. Although reovirus has not been associated with human disease, advancement in reovirus knowledge remains important as reovirus has displayed oncolytic properties in selectively infecting and killing cancer cells. The reovirus genome is composed of ten segments of dsRNA, which encodes eight structural and four non-structural proteins. The S1 genome segment encodes the viral attachment protein σ1, which forms a trimeric molecule containing tail, body, and head domains and plays an important role in target cell selection. During infection, viral attachment protein σ1 will engage membrane-bound sialylated glycan and junction adhesion molecule-A, triggering clathrin-dependent endocytosis. While the endocytic compartment is responsible for the proteolytical conversion of virions to infectious subvirion particles (ISVPs), the mechanism of ISVP exit from the endosome is unknown. Electron microscopy has revealed a distinct conformational change in σ1 from a compact form on virions to an extended form on ISVPs, inspiring the hypothesis that σ1 extension in the endosome is imperative for reovirus escape into the cytosol.To explore the importance of σ1 conformational mobility, we are introducing pairs of cysteines into structurally adjacent sites in the head, body, and tail of σ1 using reverse genetics to prevent σ1 extension and enable the quantification of mutant viral titer. These studies will enhance our understanding of non-enveloped virus entry and facilitate future σ1 modification to better selectively and efficiently target cancer cell receptors without hindering the σ1 mechanisms necessary for replication.