Catalytic (repeat 2) domain of the Protein Tyrosine Kinase, Janus kinase 1
PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. Jak1 is widely expressed in many tissues. Many cytokines are dependent on Jak1 for signaling, including those that use the shared receptor subunits common gamma chain (IL-2, IL-4, IL-7, IL-9, IL-15, IL-21) and gp130 (IL-6, IL-11, oncostatin M, G-CSF, and IFNs, among others). The many varied interactions of Jak1 and its ubiquitous expression suggest many biological roles. Jak1 is important in neurological development, as well as in lymphoid development and function. It also plays a role in the pathophysiology of cardiac hypertrophy and heart failure. A mutation in the ATP-binding site of Jak1 was identified in a human uterine leiomyosarcoma cell line, resulting in defective cytokine induction and antigen presentation, thus allowing the tumor to evade the immune system. Jak1 is a member of the Janus kinase (Jak) subfamily of proteins, which are cytoplasmic (or nonreceptor) PTKs containing an N-terminal FERM domain, followed by a Src homology 2 (SH2) domain, a pseudokinase domain, and a C-terminal tyr kinase domain. Jaks are crucial for cytokine receptor signaling. They are activated by autophosphorylation upon cytokine-induced receptor aggregation, and subsequently trigger downstream signaling events such as the phosphorylation of signal transducers and activators of transcription (STATs). The Jak1 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.
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