Abstract：
Retrons are toxin-antitoxin systems protecting bacteria against bacteriophages via abortive infection. The Retron-Eco1 antitoxin is formed by a reverse transcriptase (RT) and a non-coding RNA (ncRNA)/multi-copy single-stranded DNA (msDNA) hybrid that neutralizes an uncharacterized toxic effector. Yet, the molecular mechanisms underlying phage defense remain unknown. Here, we show that the N-glycosidase effector, which belongs to the STIR superfamily, hydrolyzes NAD+ during infection. Cryoelectron microscopy (cryo-EM) analysis shows that the msDNA stabilizes a filament that cages the effector in a low-activity state in which ADPr, a NAD+ hydrolysis product, is covalently linked to the catalytic E106 residue. Mutations shortening the msDNA induce filament disassembly and the effector\'s toxicity, underscoring the msDNA role in immunity. Furthermore, we discovered a phage-encoded Retron-Eco1 inhibitor (U56) that binds ADPr, highlighting the intricate interplay between retron systems and phage evolution. Our work outlines the structural basis of Retron-Eco1 defense, uncovering ADPr\'s pivotal role in immunity.
摘要：
Retrons是毒素-抗毒素系统，可通过流产感染保护细菌免受噬菌体的侵害。Retron-Eco1抗毒素由逆转录酶（RT）和非编码RNA（ncRNA）/多拷贝单链DNA（msDNA）杂交体形成，可中和未表征的毒性效应子。然而，噬菌体防御的分子机制仍然未知。这里,我们表明，N-糖苷酶效应子，属于STIR超家族，在感染期间水解NAD+。冷冻电子显微镜（cryo-EM）分析表明，msDNA稳定了将效应子笼罩成低活性状态的细丝，其中ADPr，NAD+水解产物，共价连接至催化E106残基。缩短msDNA的突变诱导细丝分解和效应子的毒性，强调msDNA在免疫中的作用。此外，我们发现了一种噬菌体编码的Retron-Eco1抑制剂（U56），可以结合ADPr，强调retron系统和噬菌体进化之间复杂的相互作用。我们的工作概述了Retron-Eco1防御的结构基础，揭示ADPr在免疫中的关键作用。
