Site-specific disruption of clathrin assembly produces novel structures.

Clathrin assembly in vitro produces a highly ordered polyhedral structure (basket). This resembles clathrin assembled in situ on coated pits and vesicles which form during receptor-mediated endocytosis. Sites on clathrin involved in assembly were identified by assembling clathrin in the presence of anti-clathrin monoclonal antibodies. Three of the antibodies, as IgG, prevented the assembly of normal baskets, and their Fab fragments induced formation of two types of novel clathrin structures. Antibody effects on assembly and competitive binding data indicate these antibodies bind to two sites, critical for clathrin interactions, located in the same region of the clathrin heavy chain. Analysis of novel structures formed, suggested that nucleation but not further assembly was occurring, implying an ordered sequence of clathrin interactions during assembly.