Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093, USA.
Mol Cell. 2022 Nov 3;82(21):4145-4159.e7. doi: 10.1016/j.molcel.2022.09.008. Epub 2022 Oct 6.
Self versus non-self discrimination is a key element of innate and adaptive immunity across life. In bacteria, CRISPR-Cas and restriction-modification systems recognize non-self nucleic acids through their sequence and their methylation state, respectively. Here, we show that the Wadjet defense system recognizes DNA topology to protect its host against plasmid transformation. By combining cryoelectron microscopy with cross-linking mass spectrometry, we show that Wadjet forms a complex similar to the bacterial condensin complex MukBEF, with a novel nuclease subunit similar to a type II DNA topoisomerase. Wadjet specifically cleaves closed-circular DNA in a reaction requiring ATP hydrolysis by the structural maintenance of chromosome (SMC) ATPase subunit JetC, suggesting that the complex could use DNA loop extrusion to sense its substrate's topology, then specifically activate the nuclease subunit JetD to cleave plasmid DNA. Overall, our data reveal how bacteria have co-opted a DNA maintenance machine to specifically recognize and destroy foreign DNAs through topology sensing.
自我与非我识别是贯穿生命的先天免疫和适应性免疫的关键要素。在细菌中，CRISPR-Cas 和限制修饰系统分别通过其序列和甲基化状态识别非我核酸。在这里，我们表明，Wadjet 防御系统通过识别 DNA 拓扑结构来保护其宿主免受质粒转化。通过结合冷冻电子显微镜和交联质谱，我们表明 Wadjet 形成了类似于细菌凝聚素复合物 MukBEF 的复合物，其中有一个新颖的核酸酶亚基类似于 II 型 DNA 拓扑异构酶。Wadjet 特异性地切割需要结构维持染色体 (SMC) ATP 酶亚基 JetC 水解 ATP 的闭环 DNA，这表明该复合物可以利用 DNA 环伸出来感知其底物的拓扑结构，然后特异性地激活核酸酶亚基 JetD 来切割质粒 DNA。总的来说，我们的数据揭示了细菌如何通过拓扑感应来特异地识别和破坏外源 DNA，从而利用一种 DNA 维护机器。
