RADAR is a two-protein bacterial defense system that was reported to defend against phage by “editing” messenger RNA. Here, we determine cryo-EM structures of the RADAR defense complex, revealing RdrA as a heptameric, two-layered AAA+ ATPase and RdrB as a dodecameric, hollow complex with twelve surface-exposed deaminase active sites. RdrA and RdrB join to form a giant assembly up to 10 MDa, with RdrA docked as a funnel over the RdrB active site. Surprisingly, our structures reveal an RdrB active site that targets mononucleotides. We show that RdrB catalyzes ATP-to-ITP conversion in vitro and induces the massive accumulation of inosine mononucleotides during phage infection in vivo, limiting phage replication. Our results define ATP mononucleotide deamination as a determinant of RADAR immunity and reveal supramolecular assembly of a nucleotide-modifying machine as a mechanism of anti-phage defense.

RADAR 是一种双蛋白细菌防御系统，据报道可通过“编辑”信使 RNA 来防御噬菌体。在这里，我们确定了 RADAR 防御复合体的低温 EM 结构，揭示了 RdrA 是七聚体、双层 AAA+ ATP 酶，而 RdrB 是十二聚体、空心复合体，具有十二个表面暴露的脱氨酶活性位点。RdrA 和 RdrB 结合形成一个高达 10 MDa 的巨型组件，RdrA 作为漏斗停靠在 RdrB 活性位点上。令人惊讶的是，我们的结构揭示了一个靶向单核苷酸的 RdrB 活性位点。我们表明 RdrB在体外催化 ATP 到 ITP 的转化，并在体内噬菌体感染期间诱导肌苷单核苷酸的大量积累, 限制噬菌体复制。我们的结果将 ATP 单核苷酸脱氨基定义为雷达免疫的决定因素，并揭示了核苷酸修饰机器的超分子组装是一种抗噬菌体防御机制。