Phosphorylation of the AP2 mu subunit by AAK1 mediates high affinity binding to membrane protein sorting signals

J Cell Biol. 2002 Mar 4;156(5):791-5. doi: 10.1083/jcb.200111068. Epub 2002 Mar 4.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Protein Complex 2
  • Adaptor Proteins, Vesicular Transport
  • Animals
  • Binding Sites / physiology
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Membrane / metabolism*
  • Endocytosis / physiology*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Phosphorylation
  • Protein Transport / genetics*
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Receptors, Cell Surface / metabolism*
  • Swine


  • Adaptor Protein Complex 2
  • Adaptor Proteins, Vesicular Transport
  • Carrier Proteins
  • Membrane Proteins
  • Receptors, Cell Surface
  • AAK1 protein, human
  • Protein-Serine-Threonine Kinases