Crystallization and preliminary X-ray analysis of bacterial cytosine deaminase

Cytosine deaminase (CD) is found in prokaryotes and fungi (but not higher e ukaryotes) and catalyzes the deamination of cytosine and 5-fluorocytosine t o uracil and 5-fluorouracil, respectively. The former activity is an import ant function within the pyrimidine-salvage pathway, while the latter activi ty allows the formation of a cytotoxic chemotherapeutic agent from a non-cy totoxic 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 Angstrom and diffract to at least 1.5 Angstrom resolution a t a synchrotron X-ray source. There is one enzyme subunit per asymmetric un it and the Matthews coefficient V-M is 2.8 Angstrom (3) Da(-1), correspondi ng to a solvent content of 56%. Selenomethionine-containing protein has bee n prepared and crystallized for MAD phasing.