We studied structural and immunological properties of the SARS-CoV M (membrane) protein, based on comparative analyses of sequence features, phylogenetic investigation, and experimental results. The M protein is predicted to contain a triple-spanning transmembrane (TM) region, a single N-glycosylation site near its N-terminus that is in the exterior of the virion, and a long C-terminal region in the interior. The M protein harbors a higher substitution rate (0.6% correlated to its size) among viral open reading frames (ORFs) from published data. The four substitutions detected in the M protein, which cause non-synonymous changes, can be classified into three types. One of them results in changes of pI (isoelectric point) and charge, affecting antigenicity. The second changes hydrophobicity of the TM region, and the third one relates to hydrophilicity of the interior structure. Phylogenetic tree building based on the variations of the M protein appears to support the non-human origin of SARS-CoV. To investigate its immunogenicity, we synthesized eight oligopeptides covering 69.2% of the entire ORF and screened them by using ELISA (enzyme-linked immunosorbent assay) with sera from SARS patients. The results confirmed our predictions on antigenic sites.

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Fig. 1

The distribution of GC content…

Fig. 1

The distribution of GC content (I), charge (II), the predicted hydrophobicity and antigenicity…

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Fig. 2

The predicted transmembrane domains of…

Fig. 2

The predicted transmembrane domains of the M protein.

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Fig. 3

Predicted signal peptides and cleavage…

Fig. 3

Predicted signal peptides and cleavage sites of the M protein in six coronaviruses.

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Fig. 4

The predicted transmembrane domains in…

Fig. 4

The predicted transmembrane domains in six coronaviruses.

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Fig. 5

The multiple alignments of amino…

Fig. 5

The multiple alignments of amino acid sequences of the M protein in 12…

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Fig. 6

A phylogenetic tree of the…

Fig. 6

A phylogenetic tree of the coronaviruses based on the M protein. A: ClustalW,…

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Fig. 7

The immunoassay of oligopeptides in…

Fig. 7

The immunoassay of oligopeptides in a 96-well plate. The sample distribution listed in…

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Fig. 8

The average immune reactivity of…

Fig. 8

The average immune reactivity of 8 oligopeptides by ELISA. Four oligopeptides show higher…

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Fig. 9

A diagram of the predicted…

Fig. 9

A diagram of the predicted TM structure in the SARS-CoV M protein.