Background: Xenorhabdus nematophila maintains species-specific mutual interaction with nematodes of Steinernema genus. Type II Toxin Antitoxin (TA) systems, the mazEF TA system controls stress and programmed cell death in bacteria.

Objective: This study elucidates the functional characterization of Xn-mazEF, a mazEF homolog in X. nematophila by computational and in vitro approaches.

Methods: 3D- structural models for Xn-MazE toxin and Xn-MazF antitoxin were generated, validated and characterized for protein - RNA interaction analysis. Further biological and cellular functions of Xn-MazF toxin were also predicted. Molecular dynamics simulations of 50ns for Xn- MazF toxin complexed with nucleic acid units (DU, RU, RC, and RU) were performed. The MazF toxin and complete MazEF operon were endogenously expressed and monitored for the killing of Escherichia coli host cells under arabinose induced tightly regulated system.

Results: Upon induction, E. coli expressing toxin showed rapid killing within four hours and attained up to 65% growth inhibition, while the expression of the entire operon did not show significant killing. The observation suggests that the Xn-mazEF TA system control transcriptional regulation in X. nematophila and helps to manage stress or cause toxicity leading to programmed death of cells.

Conclusion: The study provides insights into structural and functional features of novel toxin, Xn- MazF and provides an initial inference on control of X. nematophila growth regulated by TA systems.

背景：Xenorhabdus nematophila 与 Steinernema 属的线虫保持物种特异性的相互作用。II 型毒素抗毒素 (TA) 系统，即 MazEF TA 系统控制细菌中的压力和程序性细胞死亡。

目的：本研究通过计算和体外方法阐明了 Xn-mazEF 的功能特征，Xn-mazEF 是 X. nematophila 中的 MazEF 同源物。

方法：生成、验证和表征 Xn-MazE 毒素和 Xn-MazF 抗毒素的 3D 结构模型，用于蛋白质-RNA 相互作用分析。还预测了 Xn-MazF 毒素的进一步生物学和细胞功能。对与核酸单元（DU、RU、RC 和 RU）复合的 Xn-MazF 毒素进行了 50ns 的分子动力学模拟。MazF 毒素和完整的 MazEF 操纵子被内源性表达并监测在阿拉伯糖诱导的严格调控系统下杀死大肠杆菌宿主细胞。

结果：诱导后，表达毒素的大肠杆菌在4小时内表现出快速杀灭，并获得高达65%的生长抑制，而整个操纵子的表达没有显示出明显的杀灭作用。观察结果表明，Xn-mazEF TA 系统控制线虫中的转录调节，并有助于控制压力或引起导致细胞程序性死亡的毒性。

结论：该研究提供了对新型毒素 Xn-MazF 的结构和功能特征的见解，并提供了对受 TA 系统调控的线虫生长控制的初步推断。