Purification, crystallization and preliminary crystallographic data for rat cytosolic selenocysteine 498 to cysteine mutant thioredoxin reductase

Mammalian cytosolic thioredoxin reductase is a homodimer of 55 kDa subunit containing an essential penultimate selenocysteine residue. An active analogue of the rat enzyme in which cysteine replaces selenocysteine has been expressed in Escherichia coli cells at high levels and purified to homogeneity. The pure enzyme contains one FAD per subunit and shows spectral properties identical to that of the wild-type thioredoxin reductase. The isolated enzyme in its oxidized and reduced forms or the enzyme complexed with NADP⁺ was crystallized by the hanging-drop vapour-diffusion method. The diffraction pattern extends to 3 Å resolution. The crystals are monoclinic, space group P2₁, with unit-cell parameters a = 78.9, b = 140.5, c = 170.8 Å, α = 94.6°. There are three dimeric molecules in the asymmetric unit.