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coronavirus Membrane (or Matrix) protein This family contains the Membrane (M) protein of coronaviruses (CoVs) including three highly pathogenic human CoVs such as Middle East respiratory syndrome (MERS)-related CoV, severe acute respiratory syndrome (SARS) CoV, and SARS-CoV-2, also known as 2019 novel CoV (2019-nCoV) or COVID-19 virus. There are five essential genes in CoVs that result in the following gene products: Spike (S) protein, Membrane (M) glycoprotein, Nucleocapsid (N), Envelope (E) protein, and the Orf1ab (a large polyprotein known as replicase/protease); all are required to produce a structurally complete viral particle. The M protein, a triple-spanning membrane protein, is the most abundant protein in the virion. It plays a central role in virion assembly and morphogenesis, and it defines the shape of the viral envelope. It is regarded as the central organizer of CoV assembly, interacting with all other major coronaviral structural proteins and turning cellular membranes into workshops where virus and host factors come together to make new virus particles. While homotypic interactions between the M proteins are the major driving force behind virion envelope formation, it needs to interact with other coronaviral structural proteins for complete virion formation. The interaction of the Spike protein with M is not required for the assembly process. However, binding of M to N protein stabilizes the nucleocapsid (N protein-RNA complex), as well as the internal core of virions, and thereby promotes completion of viral assembly. Thus, the M protein, and its interactions with other structural proteins, is necessary for the production and release of virus-like particles. |
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