Radical SAM
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Radical SAM enzymes is a superfamily of enzymes that use a [4Fe-4S]+ cluster to reductively cleave S-adenosyl-L-methionine (SAM) to generate a radical, usually a 5′-deoxyadenosyl radical (5'-dAdo), as a critical intermediate.[1][2] These enzymes utilize this radical intermediate[3] to perform diverse transformations, often to functionalize unactivated C-H bonds. Radical SAM enzymes are involved in cofactor biosynthesis, enzyme activation, peptide modification, post-transcriptional and post-translational modifications, metalloprotein cluster formation, tRNA modification, lipid metabolism, biosynthesis of antibiotics and natural products etc. The vast majority of known radical SAM enzymes belong to the radical SAM superfamily,[4][5] and have a cysteine-rich motif that matches or resembles CxxxCxxC. Radical SAM enzymes comprise the largest superfamily of metal-containing enzymes.[6]