title: Phosphorylation of the AP2 mu subunit by AAK1 mediates high affinity binding to membrane protein sorting signals.
abstract: During receptor-mediated endocytosis, AP2 complexes act as a bridge between the cargo membrane proteins and the clathrin coat by binding to sorting signals via the mu 2 subunit and to clathrin via the beta subunit. Here we show that binding of AP2 to sorting signals in vitro is regulated by phosphorylation of the mu 2 subunit of AP2. Phosphorylation of mu 2 enhances the binding affinity of AP2 for sorting motifs as much as 25-fold compared with dephosphorylated AP2. The recognition of sorting signals was not affected by the phosphorylation status of the alpha or beta 2 subunit, suggesting that phosphorylation of mu 2 is critical for regulation of AP2 binding to sorting signals. Phosphorylation of mu 2 occurs at a single threonine residue (Thr-156) and is mediated by the newly discovered adaptor-associated kinase, AAK1, which copurifies with AP2. We propose that phosphorylation of the AP2 mu 2 subunit by AAK1 ensures high affinity binding of AP2 to sorting signals of cargo membrane proteins during the initial steps of receptor-mediated endocytosis.
authors.affiliation: Institute for Biochemistry II, University of Göttingen, 37073 Göttingen, Germany.
authors.forename: Doris
authors.initials: D
authors.lastname: Ricotta
authors.forename: Sean D
authors.initials: SD
authors.lastname: Conner
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Schmid
authors.forename: Kurt
authors.initials: K
authors.lastname: von Figura
authors.forename: Stefan
authors.initials: S
authors.lastname: Honing
mesh_terms: D033962:Adaptor Protein Complex 2; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000235:genetics*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013552:Swine
chemical_list: D033962:Adaptor Protein Complex 2; D033942:Adaptor Proteins, Vesicular Transport; D002352:Carrier Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; C451304:AAK1 protein, human; D017346:Protein Serine-Threonine Kinases