Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA.
Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA.
Cell Rep. 2020 Feb 25;30(8):2655-2671.e7. doi: 10.1016/j.celrep.2020.02.003.
Non-clustered δ1- and δ2-protocadherins, close relatives of clustered protocadherins, function in cell adhesion and motility and play essential roles in neural patterning. To understand the molecular interactions underlying these functions, we used solution biophysics to characterize binding of δ1- and δ2-protocadherins, determined crystal structures of ectodomain complexes from each family, and assessed ectodomain assembly in reconstituted intermembrane junctions by cryoelectron tomography (cryo-ET). Homophilic trans (cell-cell) interactions were preferred for all δ-protocadherins, with additional weaker heterophilic interactions observed exclusively within each subfamily. As expected, δ1- and δ2-protocadherin trans dimers formed through antiparallel EC1-EC4 interfaces, like clustered protocadherins. However, no ectodomain-mediated cis (same-cell) interactions were detectable in solution; consistent with this, cryo-ET of reconstituted junctions revealed dense assemblies lacking the characteristic order observed for clustered protocadherins. Our results define non-clustered protocadherin binding properties and their structural basis, providing a foundation for interpreting their functional roles in neural patterning.
非聚类的 δ1- 和 δ2-原钙黏蛋白是聚类原钙黏蛋白的近亲，在细胞黏附和运动中发挥作用，并在神经模式形成中发挥重要作用。为了了解这些功能的分子相互作用，我们使用溶液生物物理学来表征 δ1- 和 δ2-原钙黏蛋白的结合，确定每个家族的外域复合物的晶体结构，并通过冷冻电镜断层扫描（cryo-ET）评估在重建的膜间连接中的外域组装。同种型的转（细胞-细胞）相互作用优先于所有 δ-原钙黏蛋白，除了在每个亚家族中观察到的额外较弱的异型相互作用。如预期的那样，δ1- 和 δ2-原钙黏蛋白通过 EC1-EC4 界面的反平行形成转二聚体，就像聚类原钙黏蛋白一样。然而，在溶液中无法检测到外域介导的顺式（同一细胞）相互作用；与之一致的是，重建连接的 cryo-ET 显示出密集的组装，缺乏聚类原钙黏蛋白观察到的特征顺序。我们的结果定义了非聚类原钙黏蛋白的结合特性及其结构基础，为解释它们在神经模式形成中的功能作用提供了基础。
