CRYSTALLIZATION OF CCDB

CcdB is a small dimeric protein that poisons DNA-topoisomerase II comp lexes. Its crystallization properties in terms of precipitant type, pr ecipitant concentration, pH and protein concentration have been invest igated leading to a novel crystal form which, in contrast to previousl y reported crystals, is suitable for structure determination using the multiple isomorphous replacement (MIR) method. The space group of thi s new form is C2, with unit-cell parameters a = 74.94, b = 36.24, c = 35.77 Angstrom, beta = 115.27 degrees. The asymmetric unit contains a single monomer. Flash-frozen crystals diffract to at least 1.5 Angstro m resolution, while room-temperature diffraction can be observed up to 1.6 Angstrom. The double mutant S74C/G77Q, which acts as a super-kill er, crystallizes in space group I222 (or I2(1)2(1)2(1)) with unit-cell dimensions a = 105.58, b = 105.80, c = 91.90 Angstrom. These crystals diffract to 2.5 Angstrom resolution.