Structural Insights into Radical Generation by the Radical SAM Superfamily

The radical SAM enzymes, also referred to as the AdoMet radical enzymes are a newly identified enzyme superfamily capable of catalyzing radical chemistry similar to, but more extensive than, that performed by the AdoCbl-dependent enzymes. Radical SAM enzymes all catalyze radical chemistry and are united as a superfamily by their common mechanism of radical generation. The radical SAM superfamily has been expanded by the characterization of ThiC. While studying thiamine pyrimidine biosynthesis, Downs et al. found that the protein ThiC carries out radical SAM chemistry but does not contain the conserved motif. One of the two initial radical SAM enzymes to be structurally characterized, HemN is one of the more recently biochemically characterized members of this superfamily. Of all of the radical SAM enzymes, Lysine Aminomutase (LAM) is the best characterized. The radical SAM enzyme HydE from Thermotoga maritima is one of three enzymes recently identified as essential for maturation of the hydrogenase from that organism.