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

Helicase SF1 also includes a large number of (putative) helicases from a dozen +RNA virus families belonging to two diverse phylogenetic lineages, known as the alphavirus-like (or Sindbis virus-like) supergroup (12) and the order Nidovirales (13) . More detailed studies on the SF1 helicases of two alphavirus-like viruses have recently been published. The helicase domain of the dendrolimus punctatus tetravirus (an insect virus form the Alphatetraviridae family) was found to have dsRNAunwinding activity with 5 0 -3 0 directionality (14) . The helicase domain of the plant tomato mosaic virus (ToMV; family Virgaviridae) was not characterized enzymatically, but its crystal structure revealed the two canonical RecA-like a/b domains (1A and 2A) of the helicase core (15) . Accessory domain insertions, an otherwise frequently observed phenomenon among cellular SF1 helicases, are lacking in the ToMV helicase. The SF1 helicases of nidoviruses (HEL1), one of which is the focus of this study, were characterized in some detail using bioinformatics, molecular genetics and biochemistry (see below), but structural information was lacking thus far.