Toxin–antitoxin (TA) systems, which regulate many important cellular processes, are abundantly present in prokaryotic organisms. MazEF is a common type of TA system implicated in the formation of “persisters cells” of the pathogen Mycobacterium tuberculosis, which contains 10 such systems. However, the exact function and inhibition mode of each MazF protein are not quite understood. Here, we report four high-resolution crystal structures of MazF-mt1 in various forms, including one in complex with MazE-mt1. The toxin displayed two unique interlocked loops that allow the formation of a tight dimer. These loops would open upon interacting with the MazE-mt1 antitoxin mediated by the last two helices of MazE-mt1. With our structure-based design, a mutant that could bind to the antitoxin with an enhanced affinity was produced. Combined crystallographic and biochemical studies further revealed that the binding affinity of MazE-mt1 to MazF-mt1 was mainly attributed to its α3 helical region, while the terminal helix η1 contributes very little or even negatively to the association of the pair, in stark contrast to the MazEF-mt9 system. This study provides structural insight into the binding mode and the inhibition mechanism of the MazE/F-mt1 TA pair, which may reflect the functional differences between different TA systems.

中文翻译：

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结核分枝杆菌MazEF-mt1调节中的保守构象变化。

调节许多重要细胞过程的毒素-抗毒素（TA）系统在原核生物中大量存在。MazEF是一种常见的TA系统类型，与病原体结核分枝杆菌的“粘附细胞”形成有关，其中包含10个此类系统。但是，每种MazF蛋白的确切功能和抑制方式还不太清楚。在这里，我们报告了各种形式的MazF-mt1的四个高分辨率晶体结构，其中一个与MazE-mt1复杂。毒素显示出两个独特的互锁环，可形成紧密的二聚体。当与由MazE-mt1的最后两个螺旋介导的MazE-mt1抗毒素相互作用时，这些环将打开。通过我们基于结构的设计，产生了可以以增强的亲和力结合抗毒素的突变体。结合晶体学和生化研究的结果进一步表明，MazE-mt1与MazF-mt1的结合亲和力主要归因于其α3螺旋区，而末端螺旋η1对该对缔合的贡献很小，甚至是负面的，与MazEF-mt9系统形成鲜明对比。这项研究提供了对MazE / F-mt1 TA对的结合模式和抑制机制的结构见解，这可能反映了不同TA系统之间的功能差异。