Protein Domain : Nidovirus 2-O-methyltransferase IPR046438

Type	Domain
Description	Positive-stranded RNA (RNA) viruses that belong to the order Nidovirales infect a wide range of vertebrates (families Arteriviridae and Coronaviridae) or invertebrates (Mesoniviridae and Roniviridae). Examples of nidoviruses with high economic and societal impact are the arterivirus porcine reproductive and respiratory syndrome virus (PRRSV) and the zoonotic coronaviruses (CoVs) causing severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and Covid-19 (SARS-CoV-2) in humans.The 3'-terminal region of the most conserved ORF1b in three of the four families of the order Nidovirales (except for the family Arteriviridae) encodes a 2'-O-methyltransferase (2'-O-MTase), known as non structural protein (NSP) 16 in CoV and implicated in methylation of the 5' cap structure of nidoviral mRNAs. Assembly of a cap1 structure at the 5' end of viral mRNA assists in translation and evading host defense. The cap structure consists of a 7-methylguanosine (m7G) linked to the first nucleotide of the RNA transcript through a 5'-5' triphosphate bridge. The CoV NSP16 methyltransferase forms an obligatory complex with NSP10 to efficiently convert client mRNA species from the cap-0 ((me7)G(0)pppA(1)) to the cap-1 form ((me7)G(0)pppA(1m)) by methylating the ribose 2'-O of the first nucleotide of the nascent mRNA using S-adenosyl methionine (SAM) as the methyl donor [ , , , ].The nidovirus 2'-O-MTase domain exhibits the characteristic fold of the class I MTase family, comprising a β-sheet flanked by α-helices and loops. The nidovirus 2'-O-MTase domain harbors a catalytic K-D-K-E tetrad that is conserved among 2'-O-MTases [ , , ].
Short Name	NIV_2_O_MTASE