Kampranis S C, Maxwell A
Department of Biochemistry, University of Leicester, United Kingdom.
Proc Natl Acad Sci U S A. 1996 Dec 10;93(25):14416-21. doi: 10.1073/pnas.93.25.14416.
DNA gyrase is unique among topoisomerases in its ability to introduce negative supercoils into closed-circular DNA. We have demonstrated that deletion of the C-terminal DNA-binding domain of the A subunit of gyrase gives rise to an enzyme that cannot supercoil DNA but relaxes DNA in an ATP-dependent manner. Novobiocin, a competitive inhibitor of ATP binding by gyrase, inhibits this reaction. The truncated enzyme, unlike gyrase, does not introduce a right-handed wrap when bound to DNA and stabilizes DNA crossovers; characteristics reminiscent of conventional type II topoisomerases. This new enzyme form can decatenate DNA circles with increased efficiency compared with intact gyrase and, as a result, can complement the temperature-sensitive phenotype of a parCts mutant. Thus these results suggest that the unique properties of DNA gyrase are attributable to the wrapping of DNA around the C-terminal DNA-binding domains of the A subunits and provide an insight into the mechanism of type II topoisomerases.
DNA促旋酶在拓扑异构酶中独具一格，能够将负超螺旋引入闭环DNA。我们已经证明，删除促旋酶A亚基的C端DNA结合结构域会产生一种酶，这种酶无法使DNA超螺旋化，但能以ATP依赖的方式使DNA松弛。新生霉素是促旋酶ATP结合的竞争性抑制剂，可抑制此反应。与促旋酶不同，截短的酶在与DNA结合时不会引入右手缠绕，而是稳定DNA交叉；这些特征让人联想到传统的II型拓扑异构酶。与完整的促旋酶相比，这种新的酶形式能够更高效地解开连环DNA环，因此能够弥补parCts突变体的温度敏感表型。所以，这些结果表明DNA促旋酶的独特性质归因于DNA围绕A亚基的C端DNA结合结构域的缠绕，这为II型拓扑异构酶的作用机制提供了深入见解。
