Catalytic domain of C-terminal Src kinase-like Protein Tyrosine Kinases
PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. This subfamily is composed of Csk, Chk, and similar proteins. They are cytoplasmic (or nonreceptor) PTKs containing the Src homology domains, SH3 and SH2, N-terminal to the catalytic tyr kinase domain. They negatively regulate the activity of Src kinases that are anchored to the plasma membrane. To inhibit Src kinases, Csk and Chk are translocated to the membrane via binding to specific transmembrane proteins, G-proteins, or adaptor proteins near the membrane. Csk catalyzes the tyr phosphorylation of the regulatory C-terminal tail of Src kinases, resulting in their inactivation. Chk inhibit Src kinases using a noncatalytic mechanism by simply binding to them. As negative regulators of Src kinases, Csk and Chk play important roles in cell proliferation, survival, and differentiation, and consequently, in cancer development and progression. The Csk-like 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.",