NTPase kinetics of hepatitis G virus NS3 protein and interaction with cellular proteins

Abstract

Hepatitis G virus (HGV) which was first cloned from the plasma of a patient in 1996 share sequence similarity with hepatitis C virus (HCV). HGV nonstructural protein 3 (NS3) also contains the amino acid sequence motifs typical of ATPase and RNA helicase proteins like the HCV NS3 protein. To characterize the detail biochemical property and compare it with that of HCV NS3 protein and other Flaviviridae NS3 protein, we purified HGV NS3 protein. The purified HGV NS3 protein possessed RNA-stimulated NTPase activity. Characterization of the NTPase activities of HGV NS3 showed that the optimal reaction conditions were similar to those of other Flaviviridae viral NS3 proteins. However, the kinetic analysis of NTPase activity showed that the HGV NS3 protein had several unique properties compared to the other Flaviviridae NS3 proteins. We also investigated the effect of different polynucleotides on the NTPase activity of HGV NS3 protein. HGV NS3 protein ATPase activity was greatly enhanced in the presence of homopolymer poly(U). Poly(A) has the similar effect with poly(U). Poly(G) and duplex polynucleotide have the marginal capacity to enhance the enzymatic activity. The minimal binding size for oligonucleotide of the HGV NS3 protein was determined by measuring the NTPase activity stimulated by oligonucleotides and the filter binding assay. It was about 11 nucleotides. In another series of experiment, we tried to find cellular proteins that can interact with the HGV NS3 protein using yeast two hybrid method. It was revealed that Ash/Grb2, elongation factor-1-alpha, TRAF-3, 32kDa subunit of replication protein A, heat-shock protein 86 (hsp86) and proliferation associated gene (pag) product bound to the HGV NS3 protein. These results were verified through in vitro and in vivo binding assay. These results help us understanding in vivo function of HGV NS3 protein.