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[摘要]：DNA gyrase catalyzes ATP-dependent negative supercoiling of DNA by a strand passage mechanism that requires coordinated opening and closing of three protein interfaces, the N-, DNA-, and C-gates. ATP binding to the GyrB subunits of gyrase causes dimerization and N-gate closure. The closure of the N-gate is a key step in the gyrase catalytic cycle, as it captures the DNA segment to be transported and poises gyrase toward strand passage. We show here that K+ ions are required for DNA supercoiling but are dispensable for ATP-independent DNA relaxation. Although DNA binding, distortion, wrapping, and DNA-induced narrowing of the N-gate occur in the absence of K+, nucleotide-induced N-gate closure depends on their presence. Our results provide evidence that K+ ions relay small conformational changes in the nucleotide-binding pocket to the formation of a tight dimer interface at the N-gate by connecting regions from both GyrB monomers and suggest an important role for K+ in synchronization of N-gate closure and DNA-gate opening. |
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