School of Agriculture, Sun Yat-sen University, Shenzhen, China.
Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, USA.
mBio. 2021 Feb 23;12(1):e03020-20. doi: 10.1128/mBio.03020-20.
Bacterial cells utilize toxin-antitoxin systems to inhibit self-reproduction, while maintaining viability, when faced with environmental challenges. The activation of the toxin is often coupled to the induction of cellular response pathways, such as the stringent response, in response to multiple stress conditions. Under these conditions, the cell enters a quiescent state referred to as dormancy or persistence. How toxin activation triggers persistence and induces a systemic stress response in the alphaproteobacteria remains unclear. Here, we report that in , a -encoded bacterial toxin contributes to bacterial persistence by manipulating intracellular amino acid balance. HipA2 is a serine/threonine kinase that deactivates tryptophanyl-tRNA synthetase by phosphorylation, leading to stalled protein synthesis and the accumulation of free tryptophan. An increased level of tryptophan allosterically activates the adenylyltransferase activity of GlnE that, in turn, deactivates glutamine synthetase GlnA by adenylylation. The inactivation of GlnA promotes the deprivation of glutamine in the cell, which triggers a stringent response. By screening 69 stress conditions, we find that HipBA2 responds to multiple stress signals through the proteolysis of HipB2 antitoxin by the Lon protease and the release of active HipA2 kinase, revealing a molecular mechanism that allows disparate stress conditions to be sensed and funneled into a single response pathway. To overcome various environmental challenges, bacterial cells can enter a physiologically quiescent state, known as dormancy or persistence, which balances growth and viability. In this study, we report a new mechanism by which a toxin-antitoxin system responds to harsh environmental conditions or nutrient deprivation by orchestrating a dormant state while preserving viability. The -encoded kinase functions as a toxin in , inducing bacterial persistence by disturbing the intracellular tryptophan-glutamine balance. A nitrogen regulatory circuit can be regulated by the intracellular level of tryptophan, which mimics the allosteric role of glutamine in this feedback loop. The HipBA2 module senses different types of stress conditions by increasing the intracellular level of tryptophan, which in turn breaks the tryptophan-glutamine balance and induces glutamine deprivation. Our results reveal a molecular mechanism that allows disparate environmental challenges to converge on a common pathway that results in a dormant state.
细菌细胞利用毒素-抗毒素系统来抑制自我繁殖，同时在面临环境挑战时保持生存能力。毒素的激活通常与细胞反应途径的诱导相关联，例如严格反应，以应对多种应激条件。在这些条件下，细胞进入休眠或持续状态。毒素激活如何引发持续状态以及在α变形菌中诱导全身性应激反应尚不清楚。在这里，我们报告说，在 中，一种编码细菌毒素的 HipA2 通过操纵细胞内氨基酸平衡来促进细菌的持续存在。HipA2 是一种丝氨酸/苏氨酸激酶，通过磷酸化使色氨酰-tRNA 合成酶失活，导致蛋白质合成停滞和游离色氨酸积累。增加的色氨酸水平变构激活 GlnE 的腺苷酰转移酶活性，反过来通过腺苷酰化使 GlnA 失活。GlnA 的失活促进细胞中谷氨酰胺的剥夺，从而引发严格反应。通过筛选 69 种应激条件，我们发现 HipBA2 通过 Lon 蛋白酶对 HipB2 抗毒素的蛋白水解和活性 HipA2 激酶的释放对多种应激信号做出反应，揭示了一种分子机制，允许不同的应激条件被感知并汇集到单个反应途径中。为了克服各种环境挑战，细菌细胞可以进入生理休眠或持续状态，这种状态平衡了生长和生存能力。在这项研究中，我们报告了一种新的机制，即毒素-抗毒素系统通过协调休眠状态来应对恶劣的环境条件或营养剥夺，同时保持生存能力。编码的激酶在 中作为毒素发挥作用，通过扰乱细胞内色氨酸-谷氨酰胺平衡来诱导细菌持续存在。氮调节回路可以通过细胞内色氨酸水平来调节，这模拟了该反馈环中谷氨酰胺的变构作用。HipBA2 模块通过增加细胞内色氨酸水平来感知不同类型的应激条件，这反过来又打破了色氨酸-谷氨酰胺平衡并诱导谷氨酰胺缺乏。我们的结果揭示了一种分子机制，允许不同的环境挑战汇聚到一个共同的途径上，导致休眠状态。
