InterPro: IPR014406 [NiFe]-hydrogenase-3-type complex, small subunit/NADH:quinone oxidoreductase, subunit NuoB

[NiFe] hydrogenases function in H2 metabolism in a variety of microorganisms, enabling them to use H2 as a source of reducing equivalent under aerobic and anaerobic conditions [NiFe] hydrogenases consist of two subunits, hydrogenase large and hydrogenase small. The large subunit contains the binuclear [NiFe] active site, while the small subunit binds at least one [4Fe-4S] cluster [1].

Energy-converting [NiFe] hydrogenases (or [NiFe]-hydrogenase-3-type) form a distinct group within the [NiFe] hydrogenase family [2, 3]. Members of this subgroup include:

• Hydrogenase 3 and 4 (Hyc and Hyf) from Escherichia coli
• CO-induced hydrogenase (Coo) from Rhodospirillum rubrum
• Mbh hydrogenase from Pyrococcus furiosus
• Eha and Ehb hydrogenases from Methanothermobacter species
• Ech hydrogenase from Methanosarcina barkeri

Energy-converting [NiFe] hydrogenases are membrane-bound enzymes with a six-subunit core: the large and small hydrogenase subunits, plus two hydrophilic proteins and two integral membrane proteins. Their large and small subunits show little sequence similarity to other [NiFe] hydrogenases, except for key conserved residues coordinating the active site and [FeS] cluster. However, they show considerable sequence similarity to the six-subunit, energy-conserving NADH:quinone oxidoreductases (complex I), which are present in cytoplasmic membranes of many bacteria and in inner mitochondrial membranes. However, the reactions they catalyse differ significantly from complex I. Energy-converting [NiFe] hydrogenases function as ion pumps.

This entry represents a [NiFe]-hydrogenase-3-type complex, small subunit/NADH:quinone oxidoreductase (complex I), subunit PSST/NdhK/NuoB.