The M Protein of SARS-CoV: Basic Structural and Immunological Properties

Hu, Yongwu; Wen, Jie; Tang, Lin; Zhang, Haijun; Zhang, Xiaowei; Li, Yan; Wang, Jing; Han, Yujun; Li, Guoqing; Shi, Jianping; Tian, Xiangjun; Jiang, Feng; Zhao, Xiaoqian; Wang, Jun; Liu, Siqi; Zeng, Changqing; Wang, Jian; Yang, Huanming

The comparative analysis of the genome sequences of 361 ssRNA viruses demonstrates that the M protein is uniquely present in the seventeen currently available coronavirus genomes. The analysis on the published genome sequences of ten members in the family Coronaviridae has placed the SARS virus outside the three known groups. According to the unrooted phylogenetic tree we have proposed based on the M protein, the BCoV in Group 3 would be relatively closer to SARS-CoV. This finding for the M protein differs from the phylogenetic analysis for other structural proteins of the SARS-CoV 6., 14., 15.. However, our data based on the M protein, together with other ORFs and the entire genome, lend strong support to the conclusion that SARS-CoV is a variant in Coronaviridae that has been existing in a reservoir somewhere in nature, perhaps in non-human animal(s), for a long time and has only recently found a new pathway to humans. If SARS-CoV has been latent in its original host, it might have recently gained an extraordinarily strong selective advantage to expand its host range, establishing a high virulence to humans, through or after passing into humans. Alternatively, the virus might have passed back and forth from wild animals to humans for some time, lately changing from a wild form to a potent one.