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Endocytic sites mature by continuous bending and remodeling of the clathrin coat

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Science  19 Jun 2015:
Vol. 348, Issue 6241, pp. 1369-1372
DOI: 10.1126/science.aaa9555

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Bend me, shape me: Clathrin in action

Endocytic clathrin-coated pits were among the first cellular structures described by electron microscopy over five decades ago. Despite this, the question remains: Does clathrin bind to the membrane as a flat lattice and then bend during coated pit invagination, or does clathrin assemble with a defined curvature as membranes invaginate? Avinoam et al. applied two state-of-the-art imaging approaches to resolve this conflict. They suggest that clathrin assembles into a defined flat lattice early in endocytosis, which predetermines the size of the vesicle. The assembled clathrin coat then rearranges through dynamic exchange of clathrin with the cytosolic pool to wrap around the forming vesicle.

Science, this issue p. 1369

Abstract

During clathrin-mediated endocytosis (CME), plasma membrane regions are internalized to retrieve extracellular molecules and cell surface components. Whether endocytosis occurs by direct clathrin assembly into curved lattices on the budding vesicle or by initial recruitment to flat membranes and subsequent reshaping has been controversial. To distinguish between these models, we combined fluorescence microscopy and electron tomography to locate endocytic sites and to determine their coat and membrane shapes during invagination. The curvature of the clathrin coat increased, whereas the coated surface area remained nearly constant. Furthermore, clathrin rapidly exchanged at all stages of CME. Thus, coated vesicle budding appears to involve bending of a dynamic preassembled clathrin coat.

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