SIR2-HerA, a bacterial two-protein anti-phage defense system, induces bacterial death by depleting NAD⁺ upon phage infection. Biochemical reconstitution of SIR2, HerA, and the SIR2-HerA complex reveals a dynamic assembly process. Unlike other ATPases, HerA can form various oligomers, ranging from dimers to nonamers. When assembled with SIR2, HerA forms a hexamer and converts SIR2 from a nuclease to an NAD⁺ hydrolase, representing an unexpected regulatory mechanism mediated by protein assembly. Furthermore, high concentrations of ATP can inhibit NAD⁺ hydrolysis by the SIR2-HerA complex. Cryo-EM structures of the SIR2-HerA complex reveal a giant supramolecular assembly up to 1 MDa, with SIR2 as a dodecamer and HerA as a hexamer, crucial for anti-phage defense. Unexpectedly, the HerA hexamer resembles a spiral staircase and exhibits helicase activities toward dual-forked DNA. Together, we reveal the supramolecular assembly of SIR2-HerA as a unique mechanism for switching enzymatic activities and bolstering anti-phage defense strategies.

SIR2-HerA 是一种细菌双蛋白抗噬菌体防御系统，通过在噬菌体感染时耗尽 NAD ⁺来诱导细菌死亡。 SIR2、HerA 和 SIR2-HerA 复合物的生化重建揭示了动态组装过程。与其他 ATP 酶不同，HerA 可以形成各种寡聚体，从二聚体到九聚体。当与 SIR2 组装时，HerA 形成六聚体，并将 SIR2 从核酸酶转化为 NAD ⁺水解酶，代表了蛋白质组装介导的意想不到的调节机制。此外，高浓度的 ATP 可以抑制SIR2-HerA 复合物对NAD ^{+ 的}水解。 SIR2-HerA 复合物的冷冻电镜结构揭示了一个高达 1 MDa 的巨型超分子组装体，其中 SIR2 作为十二聚体，HerA 作为六聚体，对于抗噬菌体防御至关重要。出乎意料的是，HerA 六聚体类似于螺旋楼梯，并且表现出针对双叉 DNA 的解旋酶活性。我们共同揭示了 SIR2-HerA 的超分子组装作为转换酶活性和支持抗噬菌体防御策略的独特机制。