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Catalytic domain of the Protein Tyrosine Kinase, Discoidin Domain Receptor 2 PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. DDR2 is a receptor PTK (RTK) containing an extracellular discoidin homology domain, a transmembrane segment, an extended juxtamembrane region, and an intracellular catalytic domain. The binding of the ligand, collagen, to DDR2 results in a slow but sustained receptor activation. DDR2 binds mostly to fibrillar collagens as well as collagen X. DDR2 is widely expressed in many tissues with the highest levels found in skeletal muscle, skin, kidney and lung. It is important in cell proliferation and development. Mice, with a deletion of DDR2, suffer from dwarfism and delayed healing of epidermal wounds. DDR2 also contributes to collagen (type I) regulation by inhibiting fibrillogenesis and altering the morphology of collagen fibers. It is also expressed in immature dendritic cells (DCs), where it plays a role in DC activation and function. The DDR2 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 (PI3K).
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