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Catalytic domain of the Protein Tyrosine Kinase, Csk homologous kinase PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. Chk is also referred to as megakaryocyte-associated tyrosine kinase (Matk). Chk inhibits Src kinases using a noncatalytic mechanism by simply binding to them. As a negative regulator of Src kinases, Chk may play important roles in cell proliferation, survival, and differentiation, and consequently, in cancer development and progression. Chk is expressed in brain and hematopoietic cells. Like Csk, it is a cytoplasmic (or nonreceptor) tyr kinase containing the Src homology domains, SH3 and SH2, N-terminal to the catalytic tyr kinase domain. To inhibit Src kinases that are anchored to the plasma membrane, Chk is translocated to the membrane via binding to specific transmembrane proteins, G-proteins, or adaptor proteins near the membrane. Studies in mice reveal that Chk is not functionally redundant with Csk and that it plays an important role as a regulator of immune responses. Chk also plays a role in neural differentiation in a manner independent of Src by enhancing Mapk activation via Ras-mediated signaling. The Chk 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",