Li Wei, Xing Ying, Wang Yue, Xu Tao, Song Eli, Feng Wei
National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China; College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
Structure. 2023 Jan 5;31(1):68-77.e5. doi: 10.1016/j.str.2022.11.002.
As the prototype of Sec1/Munc18 (SM) family proteins, Munc18-1 can manipulate the distinct conformations of syntaxin-1 for controlling intracellular membrane fusion. The Munc18-1-interacting domain of Mint1 (Mint1-MID) binds to Munc18-1 together with syntaxin-1 to form a Mint1-Munc18-1-syntaxin-1 complex, but the mechanism underlying the complex assembly remains unclear. Here, we determine the structure of the Mint1-MID-Munc18-1-syntaxin-1 complex. Unexpectedly, Munc18-1 recognizes Mint1-MID and syntaxin-1 simultaneously via two opposite sites. The canonical central cavity between domains 1 and 3a of Munc18-1 embraces closed syntaxin-1, whereas the non-canonical basic pocket in domain 3b captures the acidic Mint1-MID helix. The domain 3b-mediated recognition of an acidic-helical motif is distinct from other target-recognition modes of Munc18-1. Mutations in the interface between domain 3b and Mint1-MID disrupt the assembly of the Mint1-Munc18-1-syntaxin-1 complex. This work reveals a non-canonical target-binding site in Munc18-1 domain 3b for assembling the Mint1-Munc18-1-syntaxin-1 complex.
作为Sec1/Munc18（SM）家族蛋白的原型，Munc18-1可调控Syntaxin-1的不同构象以控制细胞内膜融合。Mint1的Munc18-1相互作用结构域（Mint1-MID）与Syntaxin-1一起结合到Munc18-1上，形成Mint1-Munc18-1-Syntaxin-1复合物，但该复合物组装的潜在机制仍不清楚。在此，我们确定了Mint1-MID-Munc18-1-Syntaxin-1复合物的结构。出乎意料的是，Munc18-1通过两个相对的位点同时识别Mint1-MID和Syntaxin-1。Munc18-1结构域1和3a之间的典型中央腔容纳封闭的Syntaxin-1，而结构域3b中的非典型碱性口袋捕获酸性的Mint1-MID螺旋。结构域3b介导的酸性螺旋基序识别不同于Munc18-1的其他靶标识别模式。结构域3b与Mint1-MID之间界面的突变会破坏Mint1-Munc18-1-Syntaxin-1复合物的组装。这项工作揭示了Munc18-1结构域3b中用于组装Mint1-Munc18-1-Syntaxin-1复合物的非典型靶标结合位点。
