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

One of the main discoveries of this study is that the M protein has the highest substitution rate among all the defined non-structural and structural proteins in SARS-CoV. Comparative analysis with genome sequences of all the 16 isolates has detected a total number of 4 nucleotide substitutions in the ORFs for the M protein, with an estimated overall substitution rate of 0.6% (4/666 nt). This rate is much higher than that of the ORFs for any other viral structure proteins, and even higher than the average rate of the entire genome (0.46%). It should be emphasized that all the mutations were only detected from one of the isolate genomes, and should not be taken as the equivalent of the evolution rate. We have re-estimated this rate with a simple alternative: since 16 sequences of the M protein have been used, a reasonable approximation for this mutation rate might be 0.03% (4/666×16). Using this approach, the average rate for the entire viral genome would be 0.02%, and that for the S protein would be 0.025%.