School of Biochemistry, University of Bristol, Bristol, United Kingdom.
Department of Macromolecular Structures, Centro Nacional de Biotecnologia, Consejo Superior de Investigaciones Cientificas, Madrid, Spain.
Elife. 2019 Jan 2;8:e42129. doi: 10.7554/eLife.42129.
CtIP is involved in the resection of broken DNA during the S and G2 phases of the cell cycle for repair by recombination. Acting with the MRN complex, it plays a particularly important role in handling complex DNA end structures by localised nucleolytic processing of DNA termini in preparation for longer range resection. Here we show that human CtIP is a tetrameric protein adopting a dumbbell architecture in which DNA binding domains are connected by long coiled-coils. The protein complex binds two short DNA duplexes with high affinity and bridges DNA molecules in trans. DNA binding is potentiated by dephosphorylation and is not specific for DNA end structures per se. However, the affinity for linear DNA molecules is increased if the DNA terminates with complex structures including forked ssDNA overhangs and nucleoprotein conjugates. This work provides a biochemical and structural basis for the function of CtIP at complex DNA breaks.
CtIP 参与细胞周期 S 和 G2 期断裂 DNA 的切除，以便通过重组进行修复。它与 MRN 复合物一起作用，通过局部核酶处理 DNA 末端，在进行更长距离的切除之前，对复杂的 DNA 末端结构发挥特别重要的作用。在这里，我们表明人 CtIP 是一种四聚体蛋白，采用哑铃结构，其中 DNA 结合结构域通过长螺旋卷曲连接。该蛋白复合物以高亲和力结合两个短的 DNA 双链体，并在 trans 中桥接 DNA 分子。去磷酸化可增强 DNA 结合，并且本身并不特定于 DNA 末端结构。然而，如果 DNA 以包括分叉 ssDNA 突出端和核蛋白缀合物在内的复杂结构终止，则对线性 DNA 分子的亲和力会增加。这项工作为 CtIP 在复杂 DNA 断裂处的功能提供了生化和结构基础。
