Superresolution microscopy reveals partial preassembly and subsequent bending of the clathrin coat during endocytosis
Eukaryotic cells use clathrin-mediated endocytosis to take up a large range of extracellular cargos. During endocytosis, a clathrin coat forms on the plasma membrane, but it remains controversial when and how it is remodeled into a spherical vesicle. Here, we use 3D superresolution microscopy to determine the precise geometry of the clathrin coat at endocytic sites. Through pseudo-temporal sorting, we determine the average trajectory of clathrin remodeling during endocytosis and find that clathrin coats assemble first on flat membranes to ~50% of the coat area, before they become rapidly and continuously bent. We introduce a mathematical model that assumes a positive feedback for curvature generation of the clathrin coat. This Cooperative Curvature Model agrees excellently with experimental data in three cell lines, and likely describes a general pathway for clathrin coat remodeling during endocytosis.