CRYSTAL-STRUCTURE OF THE BREAKAGE-REUNION DOMAIN OF DNA GYRASE

DNA gyrase is a type II DNA topoisomerase from bacteria that introduce s supercoils into DNA(1,2). It catalyses the breakage of a DNA duplex (the G segment), the passage of another segment (the T segment) throug h the break, and then the reunification of the break. This activity in volves the opening and dosing of a series of molecular 'gates' which i s coupled to ATP hydrolysis. Here we present the crystal structure of the 'breakage-reunion' domain of the gyrase at 2.8 Angstrom resolution . Comparison of the structure of this 59K (relative molecular mass, 59 ,000) domain with that of a 92K fragment of yeast topoisomerase II (re f. 3) reveals a very different quaternary organization, and we propose that the two structures represent two principal conformations that pa rticipate in the enzymatic pathway. The gyrase structure reveals a new dimer contact with a grooved concave surface for binding the G segmen t and a duster of conserved charged residues surrounding the active-si te tyrosines. It also shows how breakage of the G segment can occur an d, together with the topoisomerase II structure, suggests a pathway by which the T segment can be released through the second gate of the en zyme. Mutations that confer resistance to the quinolone antibacterial agents cluster at the new dimer interface, indicating how these drugs might interact with the gyrase-DNA complex.