Structural basis for the regulatory function of a complex zinc-binding domain in a replicative arterivirus helicase resembling a nonsense-mediated mRNA decay helicase

Deng, Zengqin; Lehmann, Kathleen C.; Li, Xiaorong; Feng, Chong; Wang, Guoqiang; Zhang, Qi; Qi, Xiaoxuan; Yu, Lin; Zhang, Xingliang; Feng, Wenhai; Wu, Wei; Gong, Peng; Tao, Ye; Posthuma, Clara C.; Snijder, Eric J.; Gorbalenya, Alexander E.; Chen, Zhongzhou

Previously, using bioinformatics, biochemistry and molecular genetics, it was established that nsp10 of arteriviruses and its orthologs in other nidoviruses are multi-domain proteins. Of its domains, ZBD and the HEL1 domains are critical for the enzyme's ATPase and helicase activities in vitro and for the regulation of viral replication and transcription in infected cells. Our structural and biochemical studies extended the characterization of known domains and delineated two hitherto uncharacterized domains: one (domain 1B) flanked by ZBD and HEL1, and the other (C-terminal domain) located downstream of the HEL1, with its structure remaining to be solved. Our data show that, along with ZBD, these two non-enzymatic domains may regulate HEL1 function. Given that nsp10/nsp13 is one of only three proteins whose nidovirus-wide conservation can be detected at the sequence level (19, 24, 25, 28) , the nsp10Á structure should be applicable to other nidovirus helicases, including those of PRRS viruses and coronaviruses. However, considerable size differences exist between arteri-and coronaviruses in the most conserved ZBD and HEL1 domains, whereas the 1B and C-terminal domains lack appreciable sequence conservation. Thus, helicase structures from other small-and large-genome nidoviruses will be required to fully understand the enzyme's function.