Crystallization and preliminary X-ray diffraction analysis of a fatty-acid metabolism regulatory protein, FadR, from Bacillus halodurans

FadR is an acyl-CoA-dependent transcription factor which regulates genes encoding proteins involved in fatty-acid degradation and synthesis in order to maintain lipid homeostasis. FadR from the alkaliphilic bacterium Bacillus halodurans was cloned and overexpressed in Escherichia coli. The FadR (Bh3102) protein from B. halodurans is composed of 195 amino-acid residues with a molecular mass of 22 378 Da. Crystals were obtained by the sitting-drop vapour-diffusion method and diffracted to 2.05 Å resolution. FadR was crystallized at 296 K using polyethylene glycol 3350 as a precipitant. The crystal belonged to the apparent trigonal space group P3221, with unit-cell parameters a = b = 56.34, c = 199.73 Å. The Matthews coefficient and solvent content were estimated to be 2.0 Å ³ Da ^-1 and 39.8%, respectively, assuming that the asymmetric unit contained two molecules of FadR, which was subsequently confirmed by molecular-replacement calculations.