Kurata Tatsuaki, Takegawa Masaki, Ohira Takayuki, Syroegin Egor A, Atkinson Gemma C, Johansson Marcus J O, Polikanov Yury S, Garcia-Pino Abel, Suzuki Tsutomu, Hauryliuk Vasili
Department of Experimental Medical Science, Lund University, Lund, Sweden.
Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113-8656.
bioRxiv. 2024 Jul 5:2024.07.05.602228. doi: 10.1101/2024.07.05.602228.
Translation-targeting toxic Small Alarmone Synthetases (toxSAS) are effectors of bacterial Toxin-Antitoxin systems that pyrophosphorylate the 3'-CCA end of tRNA to prevent aminoacylation. toxSAS are implicated in antiphage immunity: phage detection triggers the toxSAS activity to shut down viral production. We show that the toxSAS FaRel2 inspects the tRNA acceptor stem to specifically select tRNA and tRNA. The 1, 2, 4 and 5 base pairs the stem act as the specificity determinants. We show that the toxSASs PhRel2 and CapRel differ in tRNA specificity from FaRel2, and rationalise this through structural modelling: while the universal 3'-CCA end slots into a highly conserved CCA recognition groove, the acceptor stem recognition region is variable across toxSAS diversity. As phages use tRNA isoacceptors to overcome tRNA-targeting defences, we hypothesise that highly evolvable modular tRNA recognition allows for the escape of viral countermeasures through tRNA substrate specificity switching.
靶向翻译的毒性小 alarmone 合成酶（toxSAS）是细菌毒素 - 抗毒素系统的效应物，可将 tRNA 的 3'-CCA 末端焦磷酸化以阻止氨酰化。toxSAS 与抗噬菌体免疫有关：噬菌体检测会触发 toxSAS 活性以关闭病毒产生。我们表明，toxSAS FaRel2 检查 tRNA 受体茎以特异性选择 tRNA 和 tRNA。茎上的第 1、2、4 和 5 个碱基对充当特异性决定因素。我们表明，toxSASs PhRel2 和 CapRel 在 tRNA 特异性上与 FaRel2 不同，并通过结构建模对此进行了合理化解释：虽然通用的 3'-CCA 末端插入高度保守的 CCA 识别槽中，但受体茎识别区域在 toxSAS 的多样性中是可变的。由于噬菌体使用 tRNA 同工受体来克服针对 tRNA 的防御，我们假设高度可进化的模块化 tRNA 识别允许通过 tRNA 底物特异性切换来逃避病毒对策。
