Expression and Activity Analysis of Non-Structural Protein 2 (NS2) of Bombyx mori Densovirus Zhenjiang Strain

The gene of the non-structure protein 2 (NS2) was cloned by PCR from the genome of Bombyx mori densovirus Zhenjiang strain (BmDNV-Z), inserted into prokaryotic expression vector pET28a to construct recombinant plasmid pET28a-NS2 and then expressed in bacteria Escherichia coli BL21 (DE3). The expressed recombinant protein was identified by SDS-PAGE and Western blot analysis. Then, the recombinant protein was purified by Ni-NTA column, renatured and tested for enzyme activities. The purified NS2 protein exhibited a helicase activity unwinding double-stranded DNA substrates into single-strand primers, and higher unwinding activity to polarity substrate. Similarly, the purified NS2 protein possessed an ATPase activity and its enzyme activity was 0.276 μmol μg-1 h-1 in this study. The results indicated that the non-structure protein which encoded by the gene of BmDNV-Z NS2 possesses the biological activities of helicase and ATPase, and the helicase prefers to polarity substrates. Based on these results, it is speculated that the gene of BmDNV-Z NS2 plays an important role in the viral DNA replication.