Seventh pandemic Vibrio cholerae strains contain two pathogenicity islands that encode the DNA defense modules DdmABC and DdmDE. Here we use cryogenic electron microscopy to reveal the mechanistic basis for plasmid defense by DdmDE. A structure of the DdmD helicase-nuclease reveals it adopts an auto-inhibited dimeric architecture. The prokaryotic Argonaute protein DdmE uses a DNA guide to target plasmid DNA. A structure of the DdmDE complex, validated by in vivo mutational studies, shows that DNA binding by DdmE triggers disassembly of the DdmD dimer and loading of monomeric DdmD onto the non-target DNA strand. In vitro studies reveal that DdmD translocates in the 5′-to-3′ direction, while partially degrading the plasmid DNA. These findings provide critical insights into the mechanism of DdmDE systems in plasmid elimination.

中文翻译：

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DdmDE防御系统消除质粒的分子机制


第七次大流行霍乱弧菌菌株含有两个编码 DNA 防御模块 DdmABC 和 DdmDE 的致病岛。在这里，我们使用低温电子显微镜揭示了 DdmDE 质粒防御的机制基础。 DdmD 解旋酶-核酸酶的结构表明它采用自动抑制二聚体结构。原核 Argonaute 蛋白 DdmE 使用 DNA 引导来靶向质粒 DNA。经过体内突变研究验证的 DdmDE 复合物结构表明，DdmE 结合 DNA 会触发 DdmD 二聚体的分解，并将单体 DdmD 加载到非目标 DNA 链上。体外研究表明，DdmD 沿 5' 至 3' 方向易位，同时部分降解质粒 DNA。这些发现为 DdmDE 系统消除质粒的机制提供了重要的见解。