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Published 4 March 2002. doi:10.1083/jcb.200111068
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© The Rockefeller University Press, 0021-9525/2002/3/791 $5.00
The Journal of Cell Biology, Volume 156, Number 5, March 4, 2002 791-795

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



Doris Ricotta1, Sean D. Conner2, Sandra L. Schmid2, Kurt von Figura1 and Stefan Höning1

1 Institute for Biochemistry II, University of Göttingen, 37073 Göttingen, Germany
2 The Scripps Research Institute, La Jolla, CA 92037

Address correspondence to Stefan Höning, Institute for Biochemistry II, University of Göttingen, Heinrich-Duker-Weg 12, Göttingen 37073, Germany. Tel.: 49-551-392127. Fax.: 49-551-395979. E-mail: shoenin{at}gwdg.de

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 µ2 subunit and to clathrin via the ß subunit. Here we show that binding of AP2 to sorting signals in vitro is regulated by phosphorylation of the µ2 subunit of AP2. Phosphorylation of µ2 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 ß2 subunit, suggesting that phosphorylation of µ2 is critical for regulation of AP2 binding to sorting signals. Phosphorylation of µ2 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 µ2 subunit by AAK1 ensures high affinity binding of AP2 to sorting signals of cargo membrane proteins during the initial steps of receptor-mediated endocytosis.

Key Words: clathrin; endocytosis; receptor; trafficking; coated vesicle


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