Expression, purification, crystallization and preliminary X-ray crystallographic studies of Mycobacterium tuberculosis thioredoxin reductase

Mycobacterium tuberculosis (H37Rv), the causative agent of the dreaded disease tuberculosis, contains three thioredoxins and a single thioredoxin reductase. Thioredoxin reductase is a member of the pyridine-nucleotide disulfide oxidoreductase family of flavoenzymes. The thioredoxin reductase gene with a His tag at the C-terminus was expressed in Escherichia coli and purified. The dimeric (70 kDa) protein was incubated with 10 mM DTT for 30 min and then crystallized using the hanging-drop vapour-diffusion method in the presence of 15% PEG 3350 and phosphate-citrate buffer pH 5 at room temperature (298 K). A diffraction data set complete to 3 Angstrom resolution has been collected under cryoconditions and the space group was determined to be P4(1)2(1)2, with unit-cell parameters a=107.4, c=118.2 Angstrom. Matthews coefficient calculations revealed the presence of two monomers in the asymmetric unit.