Viral mRNA methyltransferase (MTase) (MTase)

Viral mRNA methyltransferases (MTases) are critical enzymes employed by various RNA viruses, including coronaviruses and flaviviruses, to modify the 5' end of viral transcripts (UniProt, 2023). This enzymatic process typically involves the transfer of a methyl group from S-adenosyl-L-methionine (SAM) to the N7 position of the guanine cap or the 2'-O position of the first transcribed nucleotide, resulting in a Cap-1 structure (PubMed, PMID: 32591409). The primary biological role of this modification is to mimic host mRNA, thereby evading detection by host innate immune sensors like MDA5 and IFIT1, which recognize unmethylated or Cap-0 RNA as "non-self" (Nature Communications, 2020). In the context of SARS-CoV-2, the NSP16 protein acts as the 2'-O-MTase, requiring NSP10 as a cofactor for its activity (PMC7373611). Because these enzymes are essential for viral replication and immune evasion, they are considered high-value targets for antiviral drug development. Therapeutic strategies often involve small-molecule inhibitors that compete with SAM or the RNA binding site, such as the nucleoside analog Sinefungin (PubChem). However, a major challenge in developing these inhibitors is ensuring selectivity over human homologs like CMTR1 to minimize potential toxicity (Journal of Virology, 2021).

Other names

2'-O-methyltransferaseGuanine-N7-methyltransferaseNSP16NS5mRNA cap methyltransferaseNon-structural protein 16VP39

Inhibition of the methyltransferase activity by competing with the S-adenosyl-L-methionine (SAM) binding site or the RNA substrate binding site, preventing the formation of the Cap-1 structure (PubMed, PMID: 32591409).