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Catalytic domain of the Protein Tyrosine Kinase, Axl PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. Axl is widely expressed in a variety of organs and cells including epithelial, mesenchymal, hematopoietic, as well as non-transformed cells. It is important in many cellular functions such as survival, anti-apoptosis, proliferation, migration, and adhesion. Axl was originally isolated from patients with chronic myelogenous leukemia and a chronic myeloproliferative disorder. It is overexpressed in many human cancers including colon, squamous cell, thyroid, breast, and lung carcinomas. Axl is a member of the TAM subfamily, composed of receptor PTKs (RTKs) containing an extracellular ligand-binding region with two immunoglobulin-like domains followed by two fibronectin type III repeats, a transmembrane segment, and an intracellular catalytic domain. Binding to its ligands, Gas6 and protein S, leads to receptor dimerization, autophosphorylation, activation, and intracellular signaling. The Axl subfamily is part of a larger superfamily that includes the catalytic domains of other kinases such as serine/threonine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",