The structure and function of the beta 2-adaptin appendage domain.

Area of Science:

• Cell Biology
• Molecular Biology
• Structural Biology

Background:

• The AP2 adaptor complex is crucial for clathrin-mediated endocytosis, a fundamental cellular process.
• Previous studies determined the structures of the mu 2 and alpha appendage domains of AP2.
• The beta 2-appendage domain's structure and function remained less understood.

Purpose of the Study:

• To elucidate the protein recruitment function and structure of the AP2 complex's beta 2-appendage domain.
• To investigate the binding interactions of the beta 2 appendage with clathrin and accessory proteins.

Main Methods:

• X-ray crystallography was used to determine the 1.7 A resolution structure of the beta 2-appendage domain.
• Structure-directed mutagenesis was employed to probe protein-protein interactions.
• Biochemical assays were performed to assess binding affinities and functional consequences.

Main Results:

• The beta 2-appendage domain directly binds to clathrin, AP180, epsin, and eps15 at a single site.
• Clathrin polymerization is enhanced by simultaneous binding to the beta 2 appendage and its adjacent hinge region.
• This dual binding promotes the displacement of accessory proteins from the beta 2 appendage.

Conclusions:

• The beta 2 appendage acts as a key regulatory hub in clathrin-mediated endocytosis.
• Clathrin binding to the AP2 complex facilitates the controlled release of accessory proteins at vesicle formation sites.
• This mechanism ensures efficient and regulated cargo selection and membrane scission during endocytosis.