S-adenosylmethionine-dependent methyltransferase (SAM-MTase or AdoMet-MTase) is a conserved protein domain and protein superfamily. SAM-MTase proteins are methyltransferases. There are five protein families within SAM-MTase,
SAM-MTases use S-adenosyl-L-methionine as a substrate for methylation, creating the product S-adenosyl-L-homocysteine.
Structure and subgroups All SAM-MTases contain a structurally conserved SAM-binding domain consisting of a central seven-stranded beta-sheet that is flanked by three alpha-helices per side of the sheet.
A review published in 2003 divides all methyltransferases into 5 main classes based on the structure of their catalytic domain (fold):
class I: Rossmann-like α/β, the largest subgroup. class II: TIM β/α-barrel α/β class III: tetrapyrrole methylase α/β class IV: SPOUT α/β class V: SET domain all β
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