Catalytic domain of the Protein Tyrosine Kinase, Hematopoietic cell kinase
PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. Hck is a member of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. Hck is present in myeloid and lymphoid cells that play a role in the development of cancer. It may be important in the oncogenic signaling of the protein Tel-Abl, which induces a chronic myelogenous leukemia (CML)-like disease. Hck also acts as a negative regulator of G-CSF-induced proliferation of granulocytic precursors, suggesting a possible role in the development of acute myeloid leukemia (AML). In addition, Hck is essential in regulating the degranulation of polymorphonuclear leukocytes. Genetic polymorphisms affect the expression level of Hck, which affects PMN mediator release and influences the development of chronic obstructive pulmonary disease (COPD). Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The Hck 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.
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