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Catalytic domain of the Protein Tyrosine Kinase, Tie1 Protein Tyrosine Kinase (PTK) family; Tie1; catalytic (c) domain. The PTKc family is part of a larger superfamily that includes the catalytic domains of other kinases such as protein serine/threonine kinases, RIO kinases, and phosphoinositide 3-kinase (PI3K). PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. Tie1 is a receptor tyr kinase (RTK) containing an extracellular region, a transmembrane segment, and an intracellular catalytic domain. The extracellular region contains an immunoglobulin (Ig)-like domain, three epidermal growth factor (EGF)-like domains, a second Ig-like domain, and three fibronectin type III repeats. Tie receptors are specifically expressed in endothelial cells and hematopoietic stem cells. No specific ligand has been identified for Tie1, although the angiopoietin, Ang-1, binds to Tie1 through integrins at high concentrations. In vivo studies of Tie1 show that it is critical in vascular development.
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