Multimers of the bluetongue virus nonstructural protein, NS2, possess nucleotidyl phosphatase activity: Similarities between NS2 and rotavirus NSP2

The nonstructural protein, NS2, of bluetongue virus is a nonspecific single -stranded RNA-binding protein that forms large homomultimers and accumulate s in Viral inclusion bodies of infected cells. NS2 shares these features wi th the nonstructural protein, NSP2, of rotavirus, which like BTV is a membe r of the family Reoviridae. Recently, NSP2 was shown to have an NTPase acti vity and an autokinase activity that catalyzed its phosphorylation in vitro . To examine NS2 for similar enzymatic activities, the protein was expresse d in bacteria with a C-terminal His-tag and purified to homogeneity. Recomb inant (r)NS2 possessed nonspecific RNA-binding activity and formed 8-10S ho momultimers of the same approximate size as rNSP2 homomultimers. Notably. e nzymatic assays performed with rNS2 showed that the protein hydrolyzed the alpha, beta, and gamma phosphodiester bonds of all four NTPs. Therefore, rN S2 possesses a nucleotidyl phosphatase activity instead of the NTPase activ ity of NSP2, which only hydrolyzes the gamma phosphodiester bonds of NTPs. NS2 did not exhibit any autokinase activity in vitro, unlike NSP2. However, both NS2 and NSP2 were phosphorylated in vitro by cellular kinases. Althou gh the nature of the enzymatic activities differs significantly. the fact t hat both NS2 and NSP2 hydrolyze NTPs, undergo phosphorylation, bind RNA, an d assemble into multimers consisting of 6 +/- 2 subunits suggests that they are functional homologs.