This family includes both hybrid-cluster proteins and the beta chain of carbon monoxide dehydrogenase. The hybrid-cluster proteins contain two Fe/S centres - a [4Fe-4S] cubane cluster, and a hybrid [4Fe-2S-2O] cluster. The physiological role of this protein is as yet unknown, although a role in nitrate/nitrite respiration has been suggested [1]. The prismane protein from Escherichia coli was shown to contain hydroxylamine reductase activity (NH2OH + 2e + 2 H+ -> NH3 + H2O). This activity is rather low. Hydroxylamine reductase activity was also found in CO-dehydrogenase in which the active site Ni was replaced by Fe [2]. The CO dehydrogenase contains a Ni-3Fe-2S-3O centre.

1: The hybrid-cluster protein ('prismane protein') from Escherichia coli. Characterization of the hybrid-cluster protein, redox properties of the [2Fe-2S] and [4Fe-2S-2O] clusters and identification of an associated NADH oxidoreductase containing FAD and [2F van den Berg WA, Hagen WR, van Dongen WM; Eur J Biochem 2000;267:666-676. PMID:10651802

2: Hydroxylamine reductase activity of the hybrid cluster protein from Escherichia coli. Wolfe MT, Heo J, Garavelli JS, Ludden PW; J Bacteriol 2002;184:5898-5902. PMID:12374823