Dominguez-Molina Lucia, Kurata Tatsuaki, Cepauskas Albinas, Echemendia-Blanco Dannele, Zedek Safia, Talavera-Perez Ariel, Atkinson Gemma C, Hauryliuk Vasili, Garcia-Pino Abel
Cellular and Molecular Microbiology, Faculté des Sciences, Université libre de Bruxelles (ULB), Brussels, Belgium.
Department of Experimental Medical Science, Lund University, Lund, Sweden.
Nat Chem Biol. 2025 Feb;21(2):182-192. doi: 10.1038/s41589-024-01630-4. Epub 2024 Jun 4.
Toxic small alarmone synthetase (toxSAS) enzymes constitute a family of bacterial effectors present in toxin-antitoxin and secretion systems. toxSASs act through either translation inhibition mediated by pyrophosphorylation of transfer RNA (tRNA) CCA ends or synthesis of the toxic alarmone adenosine pentaphosphate ((pp)pApp) and adenosine triphosphate (ATP) depletion, exemplified by FaRel2 and FaRel, respectively. However, structural bases of toxSAS neutralization are missing. Here we show that the pseudo-Zn finger domain (pZFD) of the ATfaRel2 antitoxin precludes access of ATP to the pyrophosphate donor site of the FaRel2 toxin, without affecting recruitment of the tRNA pyrophosphate acceptor. By contrast, (pp)pApp-producing toxSASs are inhibited by Tis1 antitoxin domains though occlusion of the pyrophosphate acceptor-binding site. Consequently, the auxiliary pZFD of AT2faRel is dispensable for FaRel neutralization. Collectively, our study establishes the general principles of toxSAS inhibition by structured antitoxin domains, with the control strategy directly coupled to toxSAS substrate specificity.
毒性小警报素合成酶（toxSAS）构成了一类存在于毒素-抗毒素和分泌系统中的细菌效应蛋白家族。toxSAS通过两种方式发挥作用，一种是通过对转运RNA（tRNA）CCA末端进行焦磷酸化介导的翻译抑制，另一种是合成毒性警报素五磷酸腺苷（(pp)pApp）并导致三磷酸腺苷（ATP）耗竭，分别以FaRel2和FaRel为例。然而，toxSAS中和作用的结构基础尚不清楚。在这里，我们表明ATfaRel2抗毒素的假锌指结构域（pZFD）可阻止ATP进入FaRel2毒素的焦磷酸供体位点，而不影响tRNA焦磷酸受体的募集。相比之下，产生(pp)pApp的toxSAS被Tis1抗毒素结构域通过封闭焦磷酸受体结合位点所抑制。因此，AT2faRel的辅助pZFD对于FaRel的中和作用是可有可无的。总的来说，我们的研究确立了结构化抗毒素结构域抑制toxSAS的一般原则，其控制策略与toxSAS底物特异性直接相关。
