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Catalytic domain of the Protein Tyrosine Kinases, Apoptosis-associated tyrosine kinases PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. The Aatyk subfamily is also referred to as the lemur tyrosine kinase (Lmtk) subfamily. It consists of Aatyk1 (Lmtk1), Aatyk2 (Lmtk2, Brek), Aatyk3 (Lmtk3), and similar proteins. Aatyk proteins are mostly receptor PTKs (RTKs) containing a transmembrane segment and a long C-terminal cytoplasmic tail with a catalytic domain. Aatyk1 does not contain a transmembrane segment and is a cytoplasmic (or nonreceptor) kinase. Aatyk proteins are classified as PTKs based on overall sequence similarity and the phylogenetic tree. However, analysis of catalytic residues suggests that Aatyk proteins may be multispecific kinases, functioning also as serine/threonine kinases. They are involved in neural differentiation, nerve growth factor (NGF) signaling, apoptosis, and spermatogenesis. The Aatyk subfamily is part of a larger superfamily that includes the catalytic domains of other kinases such as protein serine/threonine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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