Dear Editor,

Prokaryotes have evolved a multitude of defense systems that confer immunity against invasive mobile genetic elements.^1,2,3,4,5 A two-gene DNA defense module DdmDE system is found in Vibrionaceae and Lactobacillaceae family and imposes fitness advantages to the bacteria by eliminating invasive plasmids.⁶ DdmD encodes a fusion protein comprising an N-terminal superfamily 2 helicase and a C-terminal PD-(D/E)XK superfamily nuclease, while DdmE is a putative prokaryotic Argonaute-like protein that frequently engages in bacterial immunity. Although recent studies described the function and structure of DdmDE from Vibrio cholerae,^6,7,8,9 the mechanistic basis by which the DdmDE system detects and degrades plasmids is not fully understood. In particular, the process by which DdmD dimer dissociates and how the DNA is captured by the nuclease domain for degradation remain elusive.

 尊敬的编辑：

原核生物已经进化出多种防御系统，这些系统赋予对侵入性移动遗传元件的免疫力。^1,2,3,4,5 双基因 DNA 防御模块 DdmDE 系统存在于弧菌科和乳杆菌科中，通过消除侵袭性质粒为细菌带来适应性优势。⁶ DdmD 编码一种融合蛋白，包括一个 N 端超家族 2 解旋酶和一个 C 端 PD-（D/E）XK 超家族核酸酶，而 DdmE 是一种推定的原核 Argonaute 样蛋白，经常参与细菌免疫。尽管最近的研究描述了霍乱弧菌 DdmDE 的功能和结构，^6,7,8,9，但 DdmDE 系统检测和降解质粒的机制基础尚不完全清楚。特别是，DdmD 二聚体解离的过程以及 DNA 如何被核酸酶结构域捕获以进行降解仍然难以捉摸。