The Membrane glycoprotei (M) spans the viral envelope and has three domains, namely the cytoplasmic domain, the transmembrane domain, and the N hydrophilic end of the membrane. M protein is also a glycoprotein. M protein is mainly responsible for the assembly of virus particles. M protein itself acts to form a homogeneous complex. Proteins such as S, N, and E can interact with this protein to form heterogeneous complexes. M protein alone cannot induce the formation of virions It must be activated before the action of E protein before it can be assembled into virions. M protein has a highly conserved glycosylation sequence, and the interaction between the virus and the host may be related to the glycosylation of M protein. In MHV, if the O-glycosylation site is replaced by N-glycosylation, , Then the assembly efficiency of virus-like particles is significantly reduced. The M protein is also associated with the immunogenicity of the coronavirus.