1.A.117.  The Coronavirus Membrane Matrix-Protein (M-Protein) Family

The M-protein is the dominant organizing protein of the viral envelop, serving as the matrix structural protein (Fung and Liu 2018).  It is a component of the viral envelope that plays a central role in virus morphogenesis and assembly via its interactions with the other viral proteins, the Nucleocapsid (N-protein), the Spike (S-protein), the Envelope (E-protein), etc. (Rabaan et al. 2020)  It seems to have several functions. Mutations in its encoding gene allows it to functionally replace the 3a-protein viroporin (TC# 1.A.57), suggesting that the M-protein either has or can develop pore forming activity (Kuo and Masters 2010). Moreover, the sizes and topologies of these two proteins as well as the ORF 4a protein (TC# 1.A.89) are similar, with a transmembrane N-terminal half with three strongly hydrophobic TMSs and a C-terminal half that is largely hydrophilic.  Some of these proteins show 3 weakly hydrophobic peaks that may be transmembrane, but these characteristics apply to all three families, suggesting a relationship. (M. Saier, unpublished observations). The dynamics of membrane lipids and the integral M protein of SARS-CoV-2 enables it to better associate and aggregate only in a certain temperature range (i.e., ~ 30-40 degrees C) (Rath et al. 2022).