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 M protein is characterized by a typical TM (transmembrane) region composed of three putative TM domains of 80 a.a. residues that account for about one third of the entire protein. It is located between Codons 19-98 in the ORF. Its overall features are summarized in Table 1 and Fig. 1, Fig. 2. The first TM domain (TMI) is composed of 19 a.a. residues (Codons 19-37). The non-polar, neutral amino acids account for a substantial fraction (83%) of the total domain, making it strongly hydrophobic (Fig. 1, Fig. 2). The second domain (TMII) is between Codons 50-72 (23 residues), with 81% non-polar, neutral residues, and with physiochemical features similar to TMI. A lipoprotein attachment site for prokaryotic membrane is identified at Codon 53 in TMII. The first inter-TM segment between TMI and TMII has a high probability of being located in the interior. A signal peptide of 39 a.a. residues in length with a likely cleavage site between Codons 39 and 40 (AYS-NR) is predicted within the first inter-TM segment between TMI and TMII. The TMIII domain is located between Codons 76–98 (23 residues), with 68.2% non-polar, neutral residues, and thus is not as hydrophobic as the other two. The segment between TMII and TMIII is possibly located in the exterior. A lipoprotein attachment site for prokaryotic membrane is predicted at Codon 75 in this segment or at its boundary with TMIII Figure 3.