研究人员利用冷冻电镜揭示了DdmDE防御质粒的机理基础。DdmD螺旋酶-核酸酶的结构显示，它采用了一种自动抑制的二聚体结构。原核生物的Argonaute蛋白DdmE利用DNA向导靶向质粒DNA。经体内突变研究验证的DdmDE复合物结构表明，DdmE与DNA结合会触发DdmD二聚体的解体，并将单体DdmD加载到非靶标DNA链上。
体外研究显示，DdmD在5′-3′方向上进行转运，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启示。
据介绍，第七次大流行的霍乱弧菌菌株含有两个致病岛，分别编码DNA防御模块DdmABC和DdmDE。
附：英文原文
Title: Molecular mechanism of plasmid elimination by the DdmDE defense system
Author: Luuk Loeff, David W. Adams, Christelle Chanez, Sandrine Stutzmann, Laurie Righi, Melanie Blokesch, Martin Jinek
Issue&Volume: 2024-06-13
Abstract: 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.
DOI: adq0534
Source: https://www.science.org/doi/10.1126/science.adq0534