Catalytic domain of the Protein Tyrosine Kinase, Discoidin Domain Receptor 1PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. DDR1 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 DDR1 results in a slow but sustained receptor activation. DDR1 binds to all collagens tested to date (types I-IV). It is widely expressed in many tissues. It is abundant in the brain and is also found in keratinocytes, colonic mucosa epithelium, lung epithelium, thyroid follicles, and the islets of Langerhans. During embryonic development, it is found in the developing neuroectoderm. DDR1 is a key regulator of cell morphogenesis, differentiation and proliferation. It is important in the development of the mammary gland, the vasculator and the kidney. DDR1 is also found in human leukocytes, where it facilitates cell adhesion, migration, maturation, and cytokine production. The DDR1 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.