Crystallization and preliminary X-ray analysis of bacterial cytosine deaminase

Cytosine deaminase (CD) is found in prokaryotes and fungi (but not higher eukaryotes) and catalyzes the deamination of cytosine and 5-fluorocytosine to uracil and 5-fluorouracil, respectively. The former activity is an important function within the pyrimidine-salvage pathway, while the latter activity allows the formation of a cytotoxic chemotherapeutic agent from a non-cytotoxic precursor. Recombinant bacterial CD from Escherichia coli has been subcloned, overexpressed, purified and crystallized for structural analysis. The crystals belong to space group R32, with unit-cell parameters a = b = 109.1, c = 240 A and diffract to at least 1.5 A resolution at a synchrotron X-ray source. There is one enzyme subunit per asymmetric unit and the Matthews coefficient V(M) is 2.8 A(3) Da(-1), corresponding to a solvent content of 56%. Selenomethionine-containing protein has been prepared and crystallized for MAD phasing.