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

Stewart, Meredith E.; Roy, Polly

In comparison to the D265 mutation, these mutant proteins exhibited the in vitro 2 0 -O MTase activity albeit at reduced level in comparison to WT VP4. Interestingly, mutagenesis of the surrounding three residues, the putative substrate binding pocket, had less drastic effect on virus replication. Only the introduction of the triple mutation resulted in significant effect on in vivo virus replication. The diminished 2 0 -O MTase activity could have a 2-fold effect on the virus fitness; firstly decreased protein production would result in less virus progeny, and secondly the virus' inability to control the innate immune response. Previously, we and others have shown BTV proteins regulate the innate immune response during infection [25, 31] , lower viral protein production and growth may correspond with a more robust immune response early in infection.