Purification, crystallization, and preliminary X-ray diffraction studies of the flavoenzyme mercuric ion reductase from Bacillus sp. strain RC607

The flavoenzyme mercuric ion reductase from Bacillus sp. strain RC607 was purified by dye-ligand affinity chromatography. The protein was crystallized from solutions of high ionic strength, and one of the two crystal forms obtained has proven suitable for X-ray diffraction studies. Preliminary analysis showed that these crystals belong to the tetragonal space group I422. The unit cell dimensions are a = b = 180.7 Å; c = 127.9 Å. The diffraction pattern extends to better than 3 Å resolution. Crystal density measurements are consistent with one enzyme dimer of 2 x 69,000 Da comprising the asymmetric unit. Trypsin treatment of the native enzyme resulted in the removal of 157 amino acids at the N terminus. After purification, the remaining fragment (amino acids 158-631), which is still fully active in vitro, could be crytallized under the same conditions as native enzyme. Twinning problems, however, did not allow complete analysis of these crystals.