InterPro: IPR001327 Pyridine nucleotide-disulphide oxidoreductase, NAD-binding region

This entry describes a small NADH binding domain within a larger FAD binding domain described by IPR013027. It is found in both class I and class II oxidoreductases.

FAD flavoproteins belonging to the family of pyridine nucleotide-disulphide oxidoreductases (glutathione reductase, trypanothione reductase, lipoamide dehydrogenase, mercuric reductase, thioredoxin reductase, alkyl hydroperoxide reductase) share sequence similarity with a number of other flavoprotein oxidoreductases, in particular with ferredoxin-NAD+ reductases involved in oxidative metabolism of a variety of hydrocarbons (rubredoxin reductase, putidaredoxin reductase, terpredoxin reductase, ferredoxin-NAD+ reductase components of benzene 1,2-dioxygenase, toluene 1,2-dioxygenase, chlorobenzene dioxygenase, biphenyl dioxygenase), NADH oxidase and NADH peroxidase [1, 2, 3]. Comparison of the crystal structures of human glutathione reductase and Escherichia coli thioredoxin reductase reveals different locations of their active sites, suggesting that the enzymes diverged from an ancestral FAD/NAD(P)H reductase and acquired their disulphide reductase activities independently [3].

Despite functional similarities, oxidoreductases of this family show no sequence similarity with adrenodoxin reductases [4] and flavoprotein pyridine nucleotide cytochrome reductases (FPNCR) [5]. Assuming that disulphide reductase activity emerged later, during divergent evolution, the family can be referred to as FAD-dependent pyridine nucleotide reductases, FADPNR.

To date, 3D structures of glutathione reductase [6], thioredoxin reductase [3], mercuric reductase [7], lipoamide dehydrogenase [8], trypanothione reductase [9] and NADH peroxidase [10] have been solved. The enzymes share similar tertiary structures based on a doubly-wound alpha/beta fold, but the relative orientations of their FAD- and NAD(P)H-binding domains may vary significantly. By contrast with the FPNCR family, the folds of the FAD- and NAD(P)H-binding domains are similar, suggesting that the domains evolved by gene duplication [11].