Regulation of clathrin assembly and trimerization defined using recombinant triskelion hubs

Clathrin polymerization into a polyhedral vesicle coat drives receptor sorting at cellular membranes during endocytosis and organelle biogenesis. To study clathrin self-assembly, we expressed the C-terminal third of the clathrin heavy chain in bacteria. The recombinant fragment trimerized, bound clathrin light chains, and morphologically resembled the hub domain of the triskelion-shaped clathrin molecule. Self-assembly of recombinant hubs demonstrated a regulatory role for clathrin light chains and for the distal portions of triskelion legs in clathrin coat formation. Deletion mutagenesis of the hub localized a domain mediating light chain binding and clathrin self-assembly and mapped a transferable trimerization domain. These studies define molecular interactions controlling clathrin self-assembly and establish a recombinant system for future analysis.