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

Stewart, Meredith E.; Roy, Polly

It is clear that 2 0 -O MTase must recruit and position the newly synthesized cap0 within the catalytic site for the reaction to occur. We postulated that a disruption of the residues forming the substrate/cap binding pocket would have an effect on the overall function of the domain. The ligand interactions studies with VP4 [33] enabled us to identify three residues that may be involved in binding the cap0 and/or its recruitment. The substitution of the three residues (N311, Y334, and R367) in the cap binding pocket, whether singly or in combination, retained the upstream cap methylation activities (autoguanylation and guanylyltransferase). Initially, the N311 and Y334 residues were hypothesized to interact with the guanosine residue while R367 is in proximity of the m7 of cap0. Our autoguanylation and m7-GTP data suggest that residue R367 probably interacts with the guanosine residue while N311 interacts with the m7 as also corroborated with the ligand binding data from crystallisation studies [33] .