Department of Biochemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany; Gene Center, Ludwig-Maximilians-Universität, 81377 Munich, Germany.
Department of Biochemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany; Gene Center, Ludwig-Maximilians-Universität, 81377 Munich, Germany; Center for Integrated Protein Science, 81377 Munich, Germany.
Mol Cell. 2019 Nov 7;76(3):382-394.e6. doi: 10.1016/j.molcel.2019.07.035. Epub 2019 Sep 3.
DNA double-strand breaks (DSBs) threaten genome stability throughout life and are linked to tumorigenesis in humans. To initiate DSB repair by end joining or homologous recombination, the Mre11-nuclease Rad50-ATPase complex detects and processes diverse and obstructed DNA ends, but a structural mechanism is still lacking. Here we report cryo-EM structures of the E. coli Mre11-Rad50 homolog SbcCD in resting and DNA-bound cutting states. In the resting state, Mre11's nuclease is blocked by ATP-Rad50, and the Rad50 coiled coils appear flexible. Upon DNA binding, the two coiled coils zip up into a rod and, together with the Rad50 nucleotide-binding domains, form a clamp around dsDNA. Mre11 moves to the side of Rad50, binds the DNA end, and assembles a DNA cutting channel for the nuclease reactions. The structures reveal how Mre11-Rad50 can detect and process diverse DNA ends and uncover a clamping and gating function for the coiled coils.
DNA 双链断裂 (DSBs) 威胁着整个生命周期的基因组稳定性，并与人类的肿瘤发生有关。为了通过末端连接或同源重组启动 DSB 修复，Mre11 核酸酶 Rad50-ATP 酶复合物检测和处理各种受阻的 DNA 末端，但仍缺乏结构机制。在这里，我们报告了大肠杆菌 Mre11-Rad50 同源物 SbcCD 在静止和 DNA 结合切割状态下的冷冻电镜结构。在静止状态下，Mre11 的核酸酶被 ATP-Rad50 阻断，而 Rad50 卷曲螺旋显得灵活。结合 DNA 后，两个卷曲螺旋系紧成一根棒，并与 Rad50 核苷酸结合域一起形成一个围绕双链 DNA 的夹子。Mre11 移动到 Rad50 的一侧，结合 DNA 末端，并组装用于核酸酶反应的 DNA 切割通道。这些结构揭示了 Mre11-Rad50 如何检测和处理各种 DNA 末端，并揭示了卷曲螺旋的夹闭和门控功能。
