title: Self-association of the plasma membrane-associated clathrin assembly protein AP-2.
abstract: A self-association reaction involving the plasma membrane-associated clathrin assembly protein AP-2 has been detected by incubating AP-2 alone under solution conditions that would favor the assembly of complete coat structures if clathrin were present. Self-association was rapid, unaffected by nonionic detergents, readily reversible, and gave rise to sedimentable aggregates. Only the AP subtype AP-2 exhibited self-association: the structurally or functionally related assembly proteins AP-1 and AP-3 and unrelated proteins neither self-associated nor were incorporated into the AP-2 aggregate. AP-2 interactions responsible for self-association were of high affinity, with an apparent Kd of approximately 10(-8)M. By proteolytic dissection, the self-association domain was localized to the core of the molecule containing the intact 50- and 16-kDa polypeptides in association with the truncated 60-66-kDa moieties of the parent alpha/beta polypeptides. Self-association of the intact AP-2 molecule was pH-dependent, exhibiting an apparent pKa approximately 7.4. While it is unlikely that the large AP-2 aggregates formed in solution are themselves biologically relevant structures, the AP-2 interactions involved in their formation have properties consistent with their occurrence in intact cells and thus may be important in cellular functions of the plasma membrane-localized assembly protein.
authors.affiliation: Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
authors.forename: K A
authors.initials: KA
authors.lastname: Beck
authors.forename: J H
authors.initials: JH
authors.lastname: Keen
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D002417:Cattle; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000648:ultrastructure; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D034041:Monomeric Clathrin Assembly Proteins; D010446:Peptide Fragments / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D013329:Structure-Activity Relationship
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D002966:Clathrin; D046911:Macromolecular Substances; D034041:Monomeric Clathrin Assembly Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; C439023:clathrin assembly protein AP180