Crystallization and preliminary crystallographic analysis of Bacillus subtilis guanine deaminase

Guanine deaminase, a key enzyme in nucleotide metabolism, catalyzes the hydrolytic deamination of guanine to xanthine. The first guanine deaminase crystal from Bacillus subtilis was grown in the absence or presence of the inhibitor hypoxanthine in 30% polyethylene glycol 4000, 0.2 M ammonium acetate and 0.1 M sodium citrate pH 6.5. The crystals belong to space group C222₁, with unit-cell parameters a = 84.91, b = 90.90, c = 80.19 Å, with one dimer per asymmetric unit. The crystals diffract X-rays to beyond 1.2 Å resolution and an initial atomic model has been built based on selenomethionyl multiwavelength anomalous data at 2 Å resolution. Unexpectedly, this is the first domain-swapped structure in the cytidine deaminase superfamily.