Structure of RNA-dependent RNA polymerase from 2019-nCoV, a major antiviral drug target

Yan Gao; Liming Yan; Yucen Huang; Fengjiang Liu; Yao Zhao; Lin Cao; Tao Wang; Qianqian Sun; Zhenhua Ming; Lianqi Zhang; Ji Ge; Litao Zheng; Ying Zhang; Haofeng Wang; Yan Zhu; Chen Zhu; Tianyu Hu; Tian Hua; Bing Zhang; Xiuna Yang; Jun Li; Haitao Yang; Zhijie Liu; Wenqing Xu; Luke W. Guddat; Quan Wang; Zhiyong Lou; Zihe Rao

Although the overall architecture of 2019-nCoV nsp12-nsp7-nsp8 complex is generally similar to that of SARS-CoV with an r.m.s.d value of 0.82 for 1,078 Cɑ atoms there are key features that 40 distinguish them. First, the cryo-EM map allows us to build the structure of 2019-nCoV nsp12 covering almost all residues, presenting the first insight into the complete architecture of coronaviral RdRp. In SARS-CoV nsp12, there are seven helices with a three-stranded β-sheet at the end that make up the NiRAN domain (6) ( Fig. 2A) . Residues Y69-R118 constitute an additional structural block with three anti-parallel β-strands and one helix. Residues N215-D218 form a β-strand in 2019-nCoV nsp12. We reasoned that the contact of this region with the strand (residues V96-A100) helps to stabilize it. As a result, these four strands form a compact semi βbarrel architecture. Therefore, we identify residues Y69-R249 as the complete coronaviral NiRAN domain. Second, the cryo-EM map helps us to identify a unique N-terminal β-hairpin (Figs. 1A and 2A). This β-hairpin inserts in the groove clamped by the NiRAN domain and the palm 5 subdomain in the RdRp domain and forms a set of close contacts to stabilize the overall structure ( Fig. 2B and fig. S5 ). Another point to note is that, we have observed C301-C306 and C487-C645 form disulfide bonds in the absence of DTT (Dataset-1). However, in the presence of DTT (Dataset-2), chelated zinc ions are present and in the same location as that observe in SARS-CoV ( fig. S3B) . We reasoned the different purification buffer has led to this variation.