Crystallization and preliminary X-ray diffraction analysis of a redox-sensing repressor Rex from Thermotoga maritima

The redox-sensing repressor Rex is a homodimeric transcriptional regulator involved in expression of respiratory genes. Because nicotinamide adenine dinucleotide (NAD) exists oxidized or reduced form by catabolic metabolism, intracellular NAD + /NADH ratio can be a key signal indicating the cellular redox state. The Rex from hyperthermophilic bacterium, Thermotoga maritima (TmRex), was cloned and overexpressed in Escherichia coli. The TmRex is composed of 208 amino-acid residues with a molecular mass of 22,954 Da. The TmRex crystals were obtained by the sitting-drop vapourdiffusion method and diffracted to 1.95 Å resolution. The crystals belonged to the monoclinic space group P2 1 , with unitcell parameters a = 53.54 Å, b = 88.34 Å, c = 87.84 Å, and β = 96.74°. Two dimeric molecules of TmRex were present in an asymmetric unit, giving a solvent contents of 45.17%.