AAK1

Adaptor-associated kinase 1 (AAK1), also known as AP2-associated kinase 1, is a 104 kDa serine/threonine kinase. AAK1 is expressed within the cell in the membrane and cytoplasm. It is a key endocytic kinase that is known to have two physiological substrates. AAK1 binds and phosphorylates the threonine residue at position 102 of the Numb protein. AAK1-mediated phosphorylation has been shown to be important for the endocytic activity of Numb. AAK1 is also an interacting partner of the adaptor protein 2 (AP2) complex and AAK1 recruits AP-2 to the plasma membrane. Phosphorylation of the threonine residue in the µ–subunit of AP2 (AP2M1) by AAK1 increases its binding affinity for specific tyrosine- or dileucine-based sorting signals of certain membrane receptors. It enhances cargo recruitment, vesicle assembly, and efficient internalization. AAK1 is also implicated in the regulation of various signaling pathways, such as the Notch pathway. It has been shown that AAK1 directly interacts with ligand activated Notch, but not with the inactive fulllength receptor.