ALL ABOUT ME: Pierre and co-workers have revealed mechanistic details of a tryptophan methyltransferase (TsrM) involved in the biosynthesis of the thiopeptide antibiotic, thiostrepton. Utilising cobalamin and a [4Fe-4S] cluster to generate 2-methyltryptophan from tryptophan, a key difference between this enzyme and other radical SAM methyltransferases is that the reaction is not initiated by a single-electron reduction of SAM to generate 5'-dA⋅.