Preliminary crystallographic analysis of the ATP-hydrolysing domain of the Escherichia coli DNA gyrase B protein.

The 43 kDa N-terminal ATPase domain of the Escherichia coli DNA gyrase B protein has been purified from an over-expressing strain. This protein has been crystallized in two crystal forms, both in the presence of the non-hydrolysable ATP analogue 5'-adenylyl-beta,gamma-imidodiphosphate. The first crystal form is monoclinic P2(1), with cell dimensions a = 76 A, b = 88 A, c = 82 A, beta = 105.5 degrees, and diffracts to at least 2.7 A resolution using synchrotron radiation. Crystal density measurements suggest that there are two molecules in the asymmetric unit (Vm = 3.08 A3/Da). The second crystal form is orthorhombic C222(1), with cell dimensions a = 89.2 A, b = 143.1 A and c = 79.8 A. The crystals diffract to beyond 3 A and are stable for at least 100 hours when exposed to X-rays from a rotating anode source. The asymmetric unit of this crystal form appears to contain one molecule (Vm = 2.96 A3/Da). Data have already been collected to 5 A resolution from native crystals of this second form, and to 6 A resolution from three heavy-atom derivatives. Electron density maps calculated using phases obtained from these derivatives show features consistent with secondary structural elements, and have allowed the molecular boundary to be determined. Higher resolution native and derivative data are being collected.