MopB_NDH-1_NuoG2: The second domain of the NuoG subunit of the NADH-quinone oxidoreductase/NADH dehydrogenase-1 (NDH-1), found in beta- and gammaproteobacteria. The NDH-1 is the first energy-transducting complex in the respiratory chain and functions as a redox pump that uses the redox energy to translocate H+ ions across the membrane, resulting in a significant contribution to energy production. In Escherichia coli NDH-1, the largest subunit is encoded by the nuoG gene, and is part of the 14 distinct subunits constituting the functional enzyme. The NuoG subunit is made of two domains: the first contains three binding sites for FeS clusters (the fer2 domain), the second domain (this CD), is of unknown function or, as postulated, has lost an ancestral formate dehydrogenase activity that became redundant during the evolution of the complex I enzyme. Although only vestigial sequence evidence remains of a molybdopterin binding site, this protein domain belongs to the molybdopterin_binding (MopB) superfamily of proteins.
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