Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India.
Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India; Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 004, India.
Structure. 2020 May 5;28(5):562-572.e4. doi: 10.1016/j.str.2020.03.006. Epub 2020 Apr 14.
Most biological processes involve formation of transient complexes where binding of a ligand allosterically modulates function. The ccd toxin-antitoxin system is involved in plasmid maintenance and bacterial persistence. The CcdA antitoxin accelerates dissociation of CcdB from its complex with DNA gyrase, binds and neutralizes CcdB, but the mechanistic details are unclear. Using a series of experimental and computational approaches, we demonstrate the formation of transient ternary and quaternary CcdA:CcdB:gyrase complexes and delineate the molecular steps involved in the rejuvenation process. Binding of region 61-72 of CcdA to CcdB induces the vital structural and dynamic changes required to facilitate dissociation from gyrase, region 50-60 enhances the dissociation process through additional allosteric effects, and segment 37-49 prevents gyrase rebinding. This study provides insights into molecular mechanisms responsible for recovery of CcdB-poisoned cells from a persister-like state. Similar methodology can be used to characterize other important transient, macromolecular complexes.
大多数生物过程都涉及到瞬态复合物的形成，其中配体的结合通过变构调节功能。ccd 毒素-抗毒素系统参与质粒维持和细菌持久存在。ccdA 抗毒素加速了 CcdB 与其与 DNA 拓扑异构酶复合物的解离，结合并中和 CcdB，但机制细节尚不清楚。我们使用一系列实验和计算方法，证明了瞬态三元和四元 CcdA:CcdB:gyrase 复合物的形成，并描绘了在复兴过程中涉及的分子步骤。ccdA 区域 61-72 与 CcdB 的结合诱导了从拓扑异构酶解离所需的重要结构和动态变化，区域 50-60 通过额外的变构效应增强了解离过程，而片段 37-49 防止拓扑异构酶重新结合。这项研究为从持久状态恢复 CcdB 中毒细胞的分子机制提供了深入了解。类似的方法可用于表征其他重要的瞬态、大分子复合物。
