Beyond assembly: functions of the coronavirus M protein

Coronaviruses are enveloped RNA viruses from the family Coronaviridae, notable for their crown-like spike glycoproteins. Though historically regarded as inconsequential, recent outbreaks, most notably COVID-19 caused by SARS-CoV-2, highlight their significant impact on global health. SARS-CoV-2 possesses a 27-31 kb, complex genome encoding multiple structural and non-structural proteins. The membrane/matrix (M) glycoprotein is the most abundant structural component of the viral envelope and confers the minimal requirement for virion formation. Its highly conserved structure, featuring three transmembrane domains, facilitates interactions with other viral proteins that are essential for assembly, budding, and maintaining the integrity of the viral envelope. Beyond its canonical functions in virion assembly and egress, emerging evidence suggests the M protein influences early infection processes, modulates host immune responses, and may serve as a promising antiviral target. This mini review consolidates current knowledge on the structure, multifunctional roles, and therapeutic potential of the coronavirus M protein, emphasizing the necessity for further research into its diverse functions throughout the viral lifecycle.