Highly pathogenic coronavirus N protein aggravates lung injury by MASP-2-mediated complement over-activation

Ting Gao; Mingdong Hu; Xiaopeng Zhang; Hongzhen Li; Lin Zhu; Hainan Liu; Qincai Dong; Zhang Zhang; Zhongyi Wang; Yong Hu; Yangbo Fu; Yanwen Jin; Kaitong Li; Songtao Zhao; Yongjiu Xiao; Shuping Luo; Lufeng Li; Lingfang Zhao; Junli Liu; Huailong Zhao; Yue Liu; Weihong Yang; Jing Peng; Xiaoyu Chen; Ping Li; Yaoning Liu; Yonghong Xie; Jibo Song; Lu Zhang; Qingjun Ma; Xiuwu Bian; Wei Chen; Xuan Liu; Qing Mao; Cheng Cao

SARS-CoV N protein can be detected in patient serum as early as 1 day after the onset of symptoms (22) . To simulate the SARS-CoV N protein associations in serum, Flag-tagged N protein (1 ng/ml) was added to human or mouse serum and precipitated with anti-Flag antibody conjugated agarose beads. The SARS-CoV N protein interacted with MASP-2 derived from both 20 human and mouse serum (Fig. 1B) . Further truncation and deletion analysis showed that amino acid residues 116-124, which are located in a coil motif of the SARS-CoV N protein (residues 115-130), were indispensable for the interaction with MASP-2 (Fig. 1C) . However, the association of MASP-2 with SARS-CoV N321-323, a mutant that fails to form the N protein dimer (Fig. S1C) , was not much affected (Fig. 1C) . 25 The crucial motif in SARS-CoV N protein for MASP2 interaction (residues 116-124) share a high identity with the corresponding motif in SARS-CoV-2 N (115-123) and MERS-CoV N (104-112) (Fig. S1D ), suggesting that the N protein of SARS-CoV-2 and MERS-CoV will also interact with MASP-2. As expected, exogenously expressed MERS-CoV N and SARS-CoV-2 N both associated with MASP-2 ( Fig. 1D and 1E ), and the Δ104-112 deletion mutant of MERS- 30 CoV N exhibited the predicted reduced association (Fig. 1D ). Therefore, a common motif across coronavirus N proteins is important for MASP-2 binding.