Crystal Structure of the C-Terminal Cytoplasmic Domain of Non-Structural Protein 4 from Mouse Hepatitis Virus A59

Xu, Xiaoling; Lou, Zhiyong; Ma, Yanlin; Chen, Xuehui; Yang, Zhangsheng; Tong, Xiaohang; Zhao, Qi; Xu, Yuanyuan; Deng, Hongyu; Bartlam, Mark; Rao, Zihe

Studies on a variety of RNA viruses have revealed that replication complexes are associated with cellular membranes by hydrophobic domains from non-structural proteins. Of the 16 coronavirus non-structural proteins, only nsp3, nsp4 and nsp6 are known to possess trans-membrane domains [2, 8, 24, 25, 26] and are proposed to be involved in the interaction of replication complex with the cytoplasmic membranes, either as membrane anchors or as scaffolds for the replication complex [26, 27] . Membrane topology studies concerning SARS and MHV hydrophobic domains of non-structural proteins have revealed that nsp3, nsp4 and nsp6 all have a Nendo/Cendo topology, with both the amino and carboxy terminus exposing to the cytoplasm; furthermore, two of the three hydrophobic domains of nsp3, four hydrophobic domains of nsp4 and six of the seven hydrophobic domains of nsp6 are membrane spanning [26] . These trans-membrane domains comprise of the majority part of the polyprotein pp1a, which are generally believed to mediate the assembly and targeting of replication complex to cytoplasmic membranes [28, 29, 30] , while the ORF1b-encoded proteins (nsp12-nsp16) are directly involved in coronavirus RNA replication and transcription [15, 31] .