InterPro domain: IPR019574

This entry describes the G subunit (one of 14 subunits, A to N) of the NADH-quinone oxidoreductase complex I which generally couples NADH and ubiquinone oxidation/reduction in bacteria and mammalian mitochondria while translocating protons, but may act on NADPH and/or plastoquinone in cyanobacteria and plant chloroplasts. This family does not contain related subunits from formate dehydrogenase complexes.

This entry represents the iron-sulphur binding domain of the G subunit. This domain consists of just two alpha helices separated by a loop region that coordinates a [4Fe-4S] cluster through an unusual H-x(3)-C-x(2)-C-x(5)-C motif that includes one His and three Cys residues [ 1 , 2 , 3 ].

NADH:ubiquinone oxidoreductase (complex I) ( 7.1.1.2 ) is a respiratory-chain enzyme that catalyses the transfer of two electrons from NADH to ubiquinone in a reaction that is associated with proton translocation across the membrane (NADH + ubiquinone = NAD+ + ubiquinol) [ 4 ]. Complex I is a major source of reactive oxygen species (ROS) that are predominantly formed by electron transfer from FMNH(2). Complex I is found in bacteria, cyanobacteria (as a NADH-plastoquinone oxidoreductase), archaea [ 5 ], mitochondria, and in the hydrogenosome, a mitochondria-derived organelle. In general, the bacterial complex consists of 14 different subunits, while the mitochondrial complex contains homologues to these subunits in addition to approximately 31 additional proteins [ 6 ].

1. Structural analysis of the fds operon encoding the NAD+-linked formate dehydrogenase of Ralstonia eutropha. J. Biol. Chem. 273, 26349-60
2. A novel FeS cluster in Fe-only hydrogenases. Trends Biochem. Sci. 25, 138-43
3. Iron-sulfur cluster N5 is coordinated by an HXXXCXXCXXXXXC motif in the NuoG subunit of Escherichia coli NADH:quinone oxidoreductase (complex I). J. Biol. Chem. 283, 25979-87
4. The NADH:ubiquinone oxidoreductase (complex I) of respiratory chains. Q. Rev. Biophys. 25, 253-324
5. The respiratory complex I of bacteria, archaea and eukarya and its module common with membrane-bound multisubunit hydrogenases. FEBS Lett. 479, 1-5
6. Assembly of the Escherichia coli NADH:ubiquinone oxidoreductase (complex I). Biochim. Biophys. Acta 1777, 735-9