MTase fold (class I)
Methyl transferases SAM dependent exist with several different folds. The largest group is classifed as class I Mtase otherwise referred to as the Rossmann-like structure. This enzyme may vary to catalyse N-7 or 2'O methyl-transfer . Viral MTase are encoded by most eukaryotic viruses, mainly from Varidnaviria or Riboviria realms
Origin
The MTase seven beta-strand fold occurs across all cellular life forms and many viruses, indicating an evolutionary origin that likely predates the Last Universal Cellular Ancestor (LUCA) .
Topology
Class I MTs feature an alternating alpha/beta sequence, which folds into a seven-strand sheet sandwiched by helices on each side,m creating a pocket for binding S-adenosyl methionine (SAM) .
SARS-CoV-2 nsp14 n7-MTase 8CER