Sullivan Ashley E, Nabhani Ali, Schinkel Kate, Dinh David M, Duncan Melissa L, Ednacot Eirene Marie Q, Hoffman Charlotte R K, Izrailevsky Daniel S, Kibby Emily M, Nagy Toni A, Nguyen Christy M, Tak Uday, Burroughs A Maxwell, Aravind L, Whiteley Aaron T, Morehouse Benjamin R
Department of Biochemistry, University of Colorado Boulder, Boulder, CO, USA.
Department of Molecular Biology and Biochemistry, University of California Irvine, Irvine, CA, USA.
bioRxiv. 2025 Mar 30:2025.03.28.646047. doi: 10.1101/2025.03.28.646047.
Bacteria use antiphage systems to combat phages, their ubiquitous competitors, and evolve new defenses through repeated reshuffling of basic functional units into novel reformulations. A common theme is generating a nucleotide-derived second messenger in response to phage that activates an effector protein to halt virion production. Phages respond with counter-defenses that deplete these second messengers, leading to an escalating arms race with the host. Here we discover a novel antiphage system we call Panoptes that detects phage infection by surveying the cytosol for phage proteins that antagonize the nucleotide-derived second messenger pool. Panoptes is a two-gene operon, . OptS is predicted to synthesize a second messenger using a minimal CRISPR polymerase (mCpol) domain, a version of the polymerase domain found in Type III CRISPR systems (Cas10) that is distantly related to GGDEF and Thg1 tRNA repair polymerase domains. OptE is predicted to be a transmembrane effector protein that binds cyclic nucleotides. potently restricted phage replication but mutant phages that had loss-of-function mutations in anti-CBASS protein 2 (Acb2) escaped defense. These findings were unexpected because Acb2 is a nucleotide "sponge" that antagonizes second messenger signaling. Using genetic and biochemical assays, we found that Acb2 bound the OptS-synthesized nucleotide, 2',3'-cyclic adenosine monophosphate (2',3'-c-di-AMP); however, 2',3'-c-di-AMP was synthesized constitutively by OptS and inhibited OptE. Nucleotide depletion by Acb2 released OptE toxicity thereby initiating abortive infection to halt phage replication. These data demonstrate a sophisticated immune strategy that hosts use to guard their second messenger pool and turn immune evasion against the virus.
细菌利用抗噬菌体系统对抗噬菌体（它们无处不在的竞争者），并通过将基本功能单元反复改组为新的组合来进化出新的防御机制。一个共同的主题是响应噬菌体产生一种核苷酸衍生的第二信使，该信使激活效应蛋白以阻止病毒体的产生。噬菌体则通过消耗这些第二信使的反防御机制做出反应，导致与宿主之间的军备竞赛不断升级。在这里，我们发现了一种新型的抗噬菌体系统，我们将其称为全视之眼（Panoptes），它通过在细胞质中检测与核苷酸衍生的第二信使库拮抗的噬菌体蛋白来检测噬菌体感染。全视之眼是一个双基因操纵子。OptS预计使用最小CRISPR聚合酶（mCpol）结构域合成第二信使，mCpol结构域是III型CRISPR系统（Cas10）中发现的聚合酶结构域的一个版本，与GGDEF和Thg1 tRNA修复聚合酶结构域有远缘关系。OptE预计是一种结合环核苷酸的跨膜效应蛋白。它能有效限制噬菌体复制，但在抗CBASS蛋白2（Acb2）中具有功能丧失突变的突变噬菌体逃脱了防御。这些发现出乎意料，因为Acb2是一种拮抗第二信使信号传导的核苷酸“海绵”。通过遗传和生化分析，我们发现Acb2结合了OptS合成的核苷酸2',3'-环磷酸腺苷（2',3'-c-di-AMP）；然而，2',3'-c-di-AMP是由OptS组成型合成的，并抑制OptE。Acb2导致的核苷酸消耗释放了OptE的毒性，从而引发流产感染以阻止噬菌体复制。这些数据证明了宿主用来保护其第二信使库并将免疫逃逸转向病毒的复杂免疫策略。
