Abstract：
Type II toxin-antitoxin (TA) systems are ubiquitously distributed genetic elements in prokaryotes and are crucial for cell maintenance and survival under environmental stresses. The antitoxin is a modular protein consisting of the disordered C-terminal region that physically contacts and neutralizes the cognate toxin and the well-folded N-terminal DNA binding domain responsible for autorepression of TA transcription. However, how the two functional domains communicate is largely unknown. Herein, we determined the crystal structure of the N-terminal domain of the type II antitoxin MazE-mt10 from Mycobacterium tuberculosis, revealing a homodimer of the ribbon-helix-helix (RHH) fold with distinct DNA binding specificity. NMR studies demonstrated that full-length MazE-mt10 forms the helical and coiled states in equilibrium within the C-terminal region, and that helical propensity is allosterically enhanced by the N-terminal binding to the cognate operator DNA. This coil-to-helix transition may promote toxin binding/neutralization of MazE-mt10 and further stabilize the TA-DNA transcription repressor. This is supported by many crystal structures of type II TA complexes in which antitoxins form an α-helical structure at the TA interface. The hidden helical state of free MazE-mt10 in solution, favored by DNA binding, adds a new dimension to the regulatory mechanism of type II TA systems. Furthermore, complementary approaches using X-ray crystallography and NMR allow us to study the allosteric interdomain interplay of many other full-length antitoxins of type II TA systems.
摘要：
II型毒素-抗毒素（TA）系统是原核生物中普遍存在的遗传元件，对于细胞在环境压力下的维持和生存至关重要。抗毒素是由物理接触并中和同源毒素的无序C末端区域和负责TA转录自抑制的良好折叠的N末端DNA结合结构域组成的模块化蛋白质。然而,这两个功能域如何通信在很大程度上是未知的。在这里，我们确定了结核分枝杆菌II型抗毒素MazE-mt10的N末端结构域的晶体结构，揭示了具有独特DNA结合特异性的带状螺旋-螺旋（RHH）折叠的同二聚体。NMR研究表明，全长MazE-mt10在C末端区域内形成平衡的螺旋和卷曲状态，并且该螺旋倾向通过N末端与同源操纵子DNA的结合而变构增强。这种螺旋到螺旋的转变可以促进MazE-mt10的毒素结合/中和并进一步稳定TA-DNA转录阻遏物。这得到II型TA复合物的许多晶体结构的支持，其中抗毒素在TA界面处形成α-螺旋结构。溶液中游离MazE-mt10的隐藏螺旋状态，受DNA结合的青睐，为II型TA系统的监管机制增加了新的维度。此外，使用X射线晶体学和NMR的互补方法使我们能够研究II型TA系统的许多其他全长抗毒素的变构域间相互作用。
