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Catalytic domain of the Serine/Threonine protein kinase, cyclin G-Associated Kinase STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. GAK, also called auxilin-2, contains an N-terminal kinase domain that phosphorylates the mu subunits of adaptor protein (AP) 1 and AP2. In addition, it contains an auxilin-1-like domain structure consisting of PTEN-like, clathrin-binding, and J domains. Like auxilin-1, GAK facilitates Hsc70-mediated dissociation of clathrin from clathrin-coated vesicles. GAK is expressed ubiquitously and is enriched in the Golgi, unlike auxilin-1 which is nerve-specific. GAK also plays regulatory roles outside of clathrin-mediated membrane traffic including the maintenance of centrosome integrity and chromosome congression, neural patterning, survival of neurons, and immune responses through interaction with the interleukin 12 receptor. It also interacts with the androgen receptor, acting as a transcriptional coactivator, and its expression is significantly increased with the progression of prostate cancer. The GAK subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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