Goatpoxvirus ATPase activity is increased by dsDNA and decreased by zinc ion

Viral-encoded ATPase can act as a part of molecular motor in genome packaging of DNA viruses, such as vaccinia virus and adenovirus, by ATP hydrolysis and interaction with DNA. Poxviral ATPase (also called A32) is involved in genomic double-stranded DNA (dsDNA) encapsidation, and inhibition of the expression of A32 causes formation of immature virions lacking viral DNA. However, the role of A32 in goatpoxvirus genome packaging and its dsDNA binding property are not known. In this study, purified recombinant goatpoxvirus A32 protein (rA32) was examined for its dsDNA binding property as well as the effect of dsDNA on ATP hydrolysis. We found that rA32 could bind dsDNA, and its ATPase activity was significant increased with dsDNA binding. Effects of magnesium and calcium ions on ATP hydrolysis were investigated also. The ATPase activity was dramatically enhanced by dsDNA in the presence of Mg2+; in contrast, ATPase function was not altered by Ca2+. Furthermore, the enzyme activity of rA32 was completely blocked by Zn2+. Regarding DNA–protein interaction, the rA32-ATP-Mg2+ showed lower dsDNA binding affinity than that of rA32-ATP-Ca2+. The DNA–protein binding was stronger in the presence of zinc ion. Our results implied that A32 may play a role in viral genome encapsidation and DNA condensation.