Clathrin self-assembly is mediated by a tandemly repeated superhelix

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Abstract
Clathrin is a triskelion-shaped cytoplasmic protein that polymerizes into a polyhedral lattice on intracellular membranes to form protein-coated membrane vesicles. Lattice formation induces the sorting of membrane proteins during endocytosis and organelle biogenesis by interacting with membrane-associated adaptor molecules1. The clathrin triskelion is a trimer of heavy-chain subunits (1,675 residues), each binding a single light-chain subunit, in the hub domain (residues 1,074–1,675). Light chains negatively modulate polymerization so that intracellular clathrin assembly is adaptor-dependent2. Here we report the atomic structure, to 2.6 Å resolution, of hub residues 1,210–1,516 involved in mediating spontaneous clathrin heavy-chain polymerization and light-chain association3,4. The hub fragment folds into an elongated coil of α-helices, and alignment analyses reveal a 145-residue motif that is repeated seven times along the filamentous leg and appears in other proteins involved in vacuolar protein sorting. The resulting model provides a three-dimensional framework for understanding clathrin heavy-chain self-assembly, light-chain binding and trimerization.