Clathrin-adaptor ratio and membrane tension regulate the flat-to-curved transition of the clathrin coat during endocytosis
Authors: Bucher D, Frey F, Sochacki KA, Kummer S, Bergeest JP, Godinez WJ, Kräusslich HG, Rohr K, Taraska JW, Schwarz US, Boulant S
CellNetworks People: Boulant Steeve, Kräusslich Hans-Georg, Rohr Karl, Schwarz Ulrich
Journal: Nat Commun. 2018 Mar 16;9(1):1109. doi: 10.1038/s41467-018-03533-0

Although essential for many cellular processes, the sequence of structural and molecular events during clathrin-mediated endocytosis remains elusive. While it was long believed that clathrin-coated pits grow with a constant curvature, it was recently suggested that clathrin first assembles to form flat structures that then bend while maintaining a constant surface area. Here, we combine correlative electron and light microscopy and mathematical growth laws to study the ultrastructural rearrangements of the clathrin coat during endocytosis in BSC-1 mammalian cells. We confirm that clathrin coats initially grow flat and demonstrate that curvature begins when around 70% of the final clathrin content is acquired. We find that this transition is marked by a change in the clathrin to clathrin-adaptor protein AP2 ratio and that membrane tension suppresses this transition. Our results support the notion that BSC-1 mammalian cells dynamically regulate the flat-to-curved transition in clathrin-mediated endocytosis by both biochemical and mechanical factors.