The radical SAM superfamily

Perry A. Frey, Adrian D. Hegeman, Frank J. Ruzicka

Research output: Contribution to journalReview articlepeer-review

457 Scopus citations


The radical S-adenosylmethionine (SAM) superfamily currently comprises more than 2800 proteins with the amino acid sequence motif CxxxCxxC unaccompanied by a fourth conserved cysteine. The charcteristic three-cysteine motif nucleates a [4Fe-4S] cluster, which binds SAM as a ligand to the unique Fe not ligated to a cysteine residue. The members participate in more than 40 distinct biochemical transformations, and most members have not been biochemically characterized. A handful of the members of this superfamily have been purified and at least partially characterized. Significant mechanistic and structural information is available for lysine 2,3-aminomutase, pyruvate formate-lyase, coproporphyrinogen III oxidase, and MoaA required for molybdopterin biosynthesis. Biochemical information is available for spore photoproduct lyase, anaerobic ribonucleotide reductase activation subunit, lipoyl synthase, and MiaB involved in methylthiolation of isopentenyladenine-37 in tRNA. The radical SAM enzymes biochemically characterized to date have in common the cleavage of the [4Fe-4S]1 + -SAM complex to [4Fe-4S]2 +-Met and the 5′-deoxyadenosyl radical, which abstracts a hydrogen atom from the substrate to initiate a radical mechanism.

Original languageEnglish (US)
Pages (from-to)63-88
Number of pages26
JournalCritical Reviews in Biochemistry and Molecular Biology
Issue number1
StatePublished - Jan 2008


  • 5′-deoxyadenosyl radical
  • Iron-sulfur clusters
  • Radical SAM superfamily
  • S-adenosylmethionine


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