uncharacterized subfamily of beta subunit of formate dehydrogenase
This subfamily includes the beta-subunit of formate dehydrogenases that are as yet uncharacterized. Members of the DMSO reductase family include formate dehydrogenase N and O (FDH-N, FDH-O) and tungsten-containing formate dehydrogenase (W-FDH) and other similar proteins. FDH-N, a major component of nitrate respiration of Escherichia coli, is involved in the major anaerobic respiratory pathway in the presence of nitrate, catalyzing the oxidation of formate to carbon dioxide at the expense of nitrate reduction to nitrite. It forms a heterotrimer; the alpha-subunit (FDH-G) is the catalytic site of formate oxidation and membrane-associated, incorporating a selenocysteine (SeCys) residue and a [4Fe/4S] cluster in addition to two bis-MGD cofactors, the beta subunit (FDH-H) contains four [4Fe/4S] clusters which transfer the electrons from the alpha subunit to the gamma-subunit (FDH-I), a hydrophobic integral membrane protein, presumably a cytochrome containing two b-type heme groups. W-FDH contains a tungsten instead of molybdenum at the catalytic center. This enzyme seems to be exclusively found in organisms such as hyperthermophilic archaea that live in extreme environments. It is a heterodimer of a large and a small subunit; the large subunit harbors the W site and one [4Fe-4S] center and the small subunit, containing three [4Fe-4S] clusters, functions to transfer electrons.