Structural basis for the thioredoxin-like activity profile of the glutaredoxin-like NrdH-redoxin from Escherichia coli

NrdH-redoxin is a representative of a class of small redox proteins that co ntain a conserved CXXC motif and are characterized by a glutaredoxin-like a mino acid sequence and thioredoxin-like activity profile. The crystal struc ture of recombinant Escherichia coli NrdH-redoxin in the oxidized state has been determined at 1.7 Angstrom resolution by multiwavelength anomalous di ffraction. NrdH-redoxin belongs to the thioredoxin superfamily and is struc turally most similar to E. coli glutaredoxin 3 and phage T4 glutaredoxin. T he angle between the C-terminal helix alpha3 and strand beta4, which differ s between thioredoxin and glutaredoxin, has an intermediate value in NrdH-r edoxin. The orientation of this helix is to a large extent determined by an extended hydrogen-bond network involving the highly conserved sequence mot if (61)WSG-FRP(D/E)(67), which is unique to this subclass of the thioredoxi n superfamily. Residues that bind glutathione in glutaredoxins are in gener al not conserved in NrdH-redoxin, and no glutathione-binding cleft is prese nt. Instead, NrdH-redoxin contains a wide hydrophobic pocket at the surface , similar to thioredoxin. Modeling studies suggest that NrdH-redoxin can in teract with E. coli thioredoxin reductase at this pocket and also via a loo p that is complementary to a crevice in the reductase in a similar manner a s observed in the E. coli thioredoxin-thioredoxin reductase complex.