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

The structural basis for the essential role of ZBD in EAV nsp10 helicase function Previously, ZBD mutagenesis demonstrated the in vitro and in vivo importance of this domain for nsp10 enzyme activities, genome replication and transcription, and arterivirus viability. The solved structure now provides us with a structural basis for these observations. ZBD packs against the HEL1 domains through extensive hydrophobic and hydrophilic interactions ( Figure 5A and B). Specifically, residues Leu138, Val141, Val143, Leu147, Pro247, Val248, Leu280 and Trp281 in domain 1A together with residues Ile71, Leu72, Leu75, Leu76 and Ile79 from a4 in ZBD create an extensive hydrophobic surface. The total interface area between ZBD and the HEL1 is 1019 Ã… 2 , as determined by Protein Interfaces, Surfaces and Assemblies (PISA) server (50) . A major part of this interface involves the a4 helix, which is located in a groove formed by two helices and a loop of domain 1A, while making extensive contacts to the main body of ZBD and, to lesser extent, domain 1B ( Figure 5 ). The interface areas between a4 and domain 1A, on the one hand, and the ZBD fingers (including zinc ions) on the other hand, are 558.1 and 402.4 Ã… 2 , respectively. In addition, four hydrogen bonds between ZBD and the HEL1 enhance the interaction (Figure 5B) , and a salt bridge is observed between His78 in ZBD and Asp136 in domain 1B ( Figure 5B ). The large size of these interface surfaces and the large number of interactions suggest the existence of a signalling network through which ZBD could affect both the fold and activity of HEL1.