Conformational changes in endocytic proteins are regulators of clathrin-mediated endocytosis. Three clathrin heavy chains associated with clathrin light chains (CLC) assemble into triskelia that link into a geometric lattice that curves to drive endocytosis. Structural changes in CLC have been shown to regulate triskelia assembly in solution, yet the nature of these changes, and their effects on lattice growth, curvature, and endocytosis in cells are unknown. Here, we develop a new correlative fluorescence resonance energy transfer (FRET) and platinum replica electron microscopy method, named FRET-CLEM. With FRET-CLEM, we measure conformational changes in clathrin at thousands of individual morphologically distinct clathrin-coated structures. We discover that the N-terminus of CLC repositions away from the plasma membrane and triskelia vertex as coats curve. Preventing this conformational switch with chemical tools increases lattice sizes and inhibits endocytosis. Thus, a specific conformational switch in the light chain regulates lattice curvature and endocytosis in mammalian cells.

内吞蛋白的构象变化是网格蛋白介导的内吞作用的调节因子。与网格蛋白轻链 (CLC) 相关的三个网格蛋白重链组装成三脚架，连接成一个几何格子，该格子弯曲以驱动内吞作用。CLC 的结构变化已被证明可以调节溶液中的三脚踝组装，但这些变化的性质及其对细胞晶格生长、曲率和内吞作用的影响尚不清楚。在这里，我们开发了一种新的相关荧光共振能量转移 (FRET) 和铂复制电子显微镜方法，称为 FRET-CLEM。使用 FRET-CLEM，我们测量了数千个形态不同的网格蛋白涂层结构中网格蛋白的构象变化。我们发现 CLC 的 N 端重新定位远离质膜和 triskelia 顶点作为涂层曲线。用化学工具阻止这种构象转换会增加晶格大小并抑制内吞作用。因此，轻链中的特定构象开关调节哺乳动物细胞中的晶格曲率和内吞作用。