Defense-associated sirtuin 2 (DSR2) systems are widely distributed across prokaryotic genomes, providing robust protection against phage infection. DSR2 recognizes phage tail tube proteins and induces abortive infection by depleting intracellular NAD⁺, a process that is counteracted by another phage-encoded protein, DSR Anti Defense 1 (DSAD1). Here, we present cryo-EM structures of Bacillus subtilis DSR2 in its apo, Tube-bound, and DSAD1-bound states. DSR2 assembles into an elongated tetramer, with four NADase catalytic modules clustered in the center and the regulatory-sensing modules distributed at four distal corners. Interestingly, monomeric Tube protein, rather than its oligomeric states, docks at each corner of the DSR2 tetramer to form a 4:4 DSR2-Tube assembly, which is essential for DSR2 NADase activity. DSAD1 competes with Tube for binding to DSR2 by occupying an overlapping region, thereby inhibiting DSR2 immunity. Thus, our results provide important insights into the assembly, activation and inhibition of the DSR2 anti-phage defense system.

防御相关沉默调节蛋白 2 (DSR2) 系统广泛分布于原核生物基因组中，提供针对噬菌体感染的强大保护。 DSR2 识别噬菌体尾管蛋白，并通过消耗细胞内 NAD ⁺诱导流产感染，这一过程被另一种噬菌体编码蛋白 DSR 抗防御 1 (DSAD1) 抵消。在这里，我们展示了枯草芽孢杆菌DSR2 在 apo、管结合和 DSAD1 结合状态下的冷冻电镜结构。 DSR2 组装成一个细长的四聚体，四个 NADase 催化模块聚集在中心，调节传感模块分布在四个远端角。有趣的是，单体 Tube 蛋白，而不是其寡聚状态，停靠在 DSR2 四聚体的每个角，形成 4:4 DSR2-Tube 组装体，这对于 DSR2 NADase 活性至关重要。 DSAD1 通过占据重叠区域与 Tube 竞争与 DSR2 的结合，从而抑制 DSR2 免疫。因此，我们的结果为 DSR2 抗噬菌体防御系统的组装、激活和抑制提供了重要的见解。