The enzyme, characterized from the bacterium Streptomyces laurentii, is involved in thiostrepton biosynthesis. It is a radical SAM enzyme that contains a [4Fe-4S] center and a cobalamin cofactor. The enzyme first transfers the methyl group from SAM to the bound cobalamin, followed by transfer from methylcobalamin to L-tryptophan, resulting in retention of the original methyl group configuration. The second transfer is likely to involve a CH3 radical species formed from methylcobalamin by the concerted action of a partially ligated radical SAM [4Fe-4S]2+/1+ center.
