Identification and characterization of a novel member of the radical AdoMet enzyme superfamily and implications for the biosynthesis of the Hmd hydrogenase active site cofactor

The genetic context, phylogeny, and biochemistry of a gene flanking the H(2)-forming methylene-H(4)-methanopterin dehydrogenase gene (hmdA), here designated hmdB, indicate that it is a new member of the radical S-adenosylmethionine enzyme superfamily. In contrast to the characteristic CX(3)CX(2)C or CX(2)CX(4)C motif defining this family, HmdB contains a unique CX(5)CX(2)C motif.