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

The surface of the nsp4C crystal structure suggests that the most likely candidate region for protein interaction may be the hydrophobic cavity formed by Ile419, Met453, Thr455, Tyr458, Ala461, Ala462, Gln465, Leu466, Ala469, Phe473, Val481, Leu482 Tyr483, Pro485, Pro486, Thr487 and Ala488. In the WT nsp4C structure, the Ser450-Met452 and Ala488-Thr492 loops are the most flexible regions of the molecule, but form more stable elements b3 and b4 respectively in the C425S mutant via interactions with adjacent molecules in the asymmetric unit, suggesting that interaction of these regions with other partner molecules could help to stabilize the nsp4C molecule. SARS coronavirus nsp2 reportedly interacts with nsp4 and nsp6 in vitro [39] . However, our Surface Plasmon Resonance (SPR)-based interaction assays of nsp4C with several MHV A59 nsps did not indicate any direct interaction between nsp4C and other nsps (data not shown). Since not all of the MHV ORF-encoded proteins were tested, further interaction studies are required to identify the nsp4C partner protein.