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 CX3CX2C or CX2CX4C motif defining this family, HmdB contains a unique CX5CX2C motif.