Expression, purification, crystallization and preliminary X-ray crystallographic studies of Deinococcus radiodurans thioredoxin reductase

Deinococcus radiodurans, a Gram-positive bacterium capable of withstanding extreme ionizing radiation, contains two thioredoxins (Trx and Trx1) and a single thioredoxin reductase (TrxR) as part of its response to oxidative stress. Thioredoxin reductase is a member of the family of pyridine nucleotide-disulfide oxidoreductase flavoenzymes. Recombinant D. radiodurans TrxR with a His tag at the N-terminus was expressed in Escherichia coli and purified by metal-affinity chromatography. The protein was crystallized using the sitting-drop vapour-diffusion method in the presence of 35% PEG 4000, 0.2 M ammonium acetate and citric acid buffer pH 5.1 at 293 K. X-ray diffraction data were collected on a cryocooled crystal to a resolution of 1.9 angstrom using a synchrotron-radiation source. The space group was determined to be P3(2)21, with unit-cell parameters a = b = 84.33, c = 159.88 angstrom. The structure of the enzyme has been solved by molecular-replacement methods and structure refinement is in progress.