Structure-based identification of functional residues in the nucleoside-2'-O-methylase domain of Bluetongue virus VP4 capping enzyme

Stewart, Meredith E.; Roy, Polly

Recent studies of viral cap structures have revealed the importance of the 2 0 -O methylation in evading the host innate immune response to RNA viruses [39] . Modification of the catalytic K-D-K-E tetrad within the domain has been demonstrated to render the virus replication deficient and mutations of key residues within the catalytic pocket affect the rate of methylation, which leads to attenuation [8, 13, 15] . In this report, we focused on the 2 0 -O MTase domain of VP4, which although possesses the consensus fold of the typical class I AdoMet-dependent methyltransferases and displays some structural similarities with Vaccinia virus VP39 and Dengue virus NS5 methyltransferase as well as containing some unique features, the precise roles of which are unclear. We used structural information to identify key residues within VP4 2 0 -O MT and verified their importance employing a series of biochemical assays and the BTV reverse genetics system. This is the first report to assign function to the putative 2 0 -O MT domain for the capping enzyme of any member of the Reoviridae.