MutS family proteins are classified into MutS-I and -II lineages: MutS-I recognizes mismatched DNA and initiates mismatch repair, whereas MutS-II recognizes DNA junctions to modulate recombination. MutS-I forms dimeric clamp-like structures enclosing the mismatched DNA, and its composite ATPase sites regulate DNA-binding modes. Meanwhile, the structures of MutS-II have not been determined; accordingly, it remains unknown how MutS-II recognizes DNA junctions and how nucleotides control DNA binding. Here, we solved the ligand-free and ADP-bound crystal structures of bacterial MutS2 belonging to MutS-II. MutS2 also formed a dimeric clamp-like structure with composite ATPase sites. The ADP-bound MutS2 was more flexible compared to the ligand-free form and could be more suitable for DNA entry. The inner hole of the MutS2 clamp was two times larger than that of MutS-I, and site-directed mutagenesis analyses revealed DNA-binding sites at the inner hole. Based on these, a model is proposed that describes how MutS2 recognizes DNA junctions.

MutS 家族蛋白分为 MutS-I 和 -II 谱系：MutS-I 识别错配 DNA 并启动错配修复，而 MutS-II 识别 DNA 连接以调节重组。MutS-I 形成封闭错配 DNA 的二聚体钳状结构，其复合 ATP 酶位点调节 DNA 结合模式。同时，MutS-II的结构尚未确定；因此，尚不清楚 MutS-II 如何识别 DNA 连接以及核苷酸如何控制 DNA 结合。在这里，我们解决了属于 MutS-II 的细菌 MutS2 的无配体和 ADP 结合的晶体结构。MutS2 还形成了具有复合 ATP 酶位点的二聚体钳状结构。与无配体形式相比，ADP 结合的 MutS2 更灵活，更适合 DNA 进入。MutS2 夹的内孔比 MutS-I 大两倍，定点诱变分析显示内孔处有 DNA 结合位点。基于这些，提出了一个模型来描述 MutS2 如何识别 DNA 连接。