| Type: | Family | Name: | Probable [NiFe]-hydrogenase-type-3 Eha complex membrane subunit A |
| Description: | [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 [].Energy-converting [NiFe] hydrogenases (or [NiFe]-hydrogenase-3-type) form a distinct group within the [NiFe] hydrogenase family [, ]. Members of this subgroup include:Hydrogenase 3 and 4 (Hyc and Hyf) from Escherichia coliCO-induced hydrogenase (Coo) from Rhodospirillum rubrumMbh hydrogenase from Pyrococcus furiosusEha and Ehb hydrogenases from Methanothermobacter speciesEch hydrogenase from Methanosarcina barkeriEnergy-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.Eha and Ehb hydrogenases contain extra subunits in addition to those shared by other energy-converting [NiFe] hydrogenases (or [NiFe]-hydrogenase-3-type). Eha contains a 6[4Fe-4S] polyferredoxin, a 10[4F-4S]polyferredoxin, ten other predicted integral membrane proteins (EhaA , EhaB , EhaC , EhaD , EhaE , EhaF , EhaG , EhaI , EhaK , EhaL ) and four hydrophobic subunits (EhaM, EhaR , EhS, EhT) []. The ten predicted integral membrane proteins are absent from Ech, Coo, Hyc and Hyf complexes, which may have simpler membrane components than Eha. Eha and Ehb catalyse the reduction of low-potential redox carriers (e.g. ferredoxins or polyferredoxins), which then might function as electron donors to oxidoreductases.Based on sequence similarity and genome context analysis, other organisms such as Methanopyrus kandleri, Methanocaldococcus jannaschii, and Methanothermobacter marburgensisalso encode Eha-like [NiFe]-hydrogenase-3-type complexes and have very similar ehaoperon structure.This entry represents small membrane proteins that are predicted to be the EhaA transmembrane subunits of multisubunit membrane-bound [NiFe]-hydrogenase Eha complexes. | Short Name: | Prd_NiFe_hyd_3_EhaA |
