CALM regulates clathrin-coated vesicle size and maturation by directly sensing and driving membrane curvature.

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Miller, Sharon E 
Mathiasen, Signe 
Bright, Nicholas A 
Pierre, Fabienne 
Kelly, Bernard T 

The size of endocytic clathrin-coated vesicles (CCVs) is remarkably uniform, suggesting that it is optimized to achieve the appropriate levels of cargo and lipid internalization. The three most abundant proteins in mammalian endocytic CCVs are clathrin and the two cargo-selecting, clathrin adaptors, CALM and AP2. Here we demonstrate that depletion of CALM causes a substantial increase in the ratio of "open" clathrin-coated pits (CCPs) to "necked"/"closed" CCVs and a doubling of CCP/CCV diameter, whereas AP2 depletion has opposite effects. Depletion of either adaptor, however, significantly inhibits endocytosis of transferrin and epidermal growth factor. The phenotypic effects of CALM depletion can be rescued by re-expression of wild-type CALM, but not with CALM that lacks a functional N-terminal, membrane-inserting, curvature-sensing/driving amphipathic helix, the existence and properties of which are demonstrated. CALM is thus a major factor in controlling CCV size and maturation and hence in determining the rates of endocytic cargo uptake.

Cell Line, Tumor, Cell Membrane, Cell Shape, Clathrin-Coated Vesicles, Coated Pits, Cell-Membrane, Endocytosis, Epidermal Growth Factor, Fatty Acid-Binding Proteins, HeLa Cells, Humans, Liposomes, Monomeric Clathrin Assembly Proteins, Protein Structure, Tertiary, R-SNARE Proteins, RNA Interference, RNA, Small Interfering, Transferrin
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Dev Cell
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Elsevier BV
Medical Research Council (MR/M010007/1)
Wellcome Trust (100140/Z/12/Z)
Wellcome Trust (090909/Z/09/Z)
S.E.M. and D.J.O. are funded by a Wellcome Trust Fellowship (to D.J.O. no. 090909/Z). N.A.B. is funded by MRC grant MR/M010007/1, and S.H. is funded by a grant from the German Science Foundation (SFB 635, TP A3). D.S. and S.M. acknowledge financial support from the Lundbeck Foundation and the Danish Councils for Independent and Strategic Research. C.J.M. and F.P. were funded by the Fondation pour la Recherche Medicale.