This family consists of various coronavirus matrix proteins which are transmembrane glycoproteins [1]. The membrane (M) protein is the most abundant structural protein and defines the shape of the viral envelope, being the central organiser of coronavirus assembly. M proteins play a critical role in protein-protein interactions (as well as protein-RNA interactions) since virus-like particle (VLP) formation in many CoVs requires only the M and envelope (E) proteins for efficient virion assembly [2]. Interaction of spike (S) with M is necessary for retention of S in the ER-Golgi intermediate compartment (ERGIC)/Golgi complex and its incorporation into new virions; binding of M to nucleocapsid (N) proteins stabilises the nucleocapsid. Together, M and E protein make up the viral envelope and their interaction is sufficient for the production and release of virus-like particles (VLPs)[3].

1: Sequence and topology of a model intracellular membrane protein, E1 glycoprotein, from a coronavirus. Armstrong J, Niemann H, Smeekens S, Rottier P, Warren G; Nature 1984;308:751-752. PMID:6325918

2: Incorporation of spike and membrane glycoproteins into coronavirus virions. Ujike M, Taguchi F; Viruses. 2015;7:1700-1725. PMID:25855243

3: Coronavirus envelope protein: current knowledge. Schoeman D, Fielding BC; Virol J. 2019;16:69. PMID:31133031