Pseudokinase (repeat 1) domain of the Protein Tyrosine Kinase, Janus kinase 2
Jak2 is widely expressed in many tissues. It is essential for the signaling of hormone-like cytokines such as growth hormone, erythropoietin, thrombopoietin, and prolactin, as well as some IFNs and cytokines that signal through the IL-3 and gp130 receptors. Disruption of Jak2 in mice results in an embryonic lethal phenotype with multiple defects including erythropoietic and cardiac abnormalities. It is the only Jak gene that results in a lethal phenotype when disrupted in mice. A mutation in the pseudokinase domain of Jak2, V617F, is present in many myeloproliferative diseases, including almost all patients with polycythemia vera, and 50% of patients with essential thrombocytosis and myelofibrosis. Jak2 is a cytoplasmic (or nonreceptor) PTK containing an N-terminal FERM domain, followed by a Src homology 2 (SH2) domain, a pseudokinase domain, and a C-terminal tyr kinase domain. The pseudokinase domain shows similarity to tyr kinases but lacks crucial residues for catalytic activity and ATP binding. Despite this, the presumed pseudokinase (repeat 1) domain of Jak2 exhibits dual-specificity kinase activity, phosphorylating two negative regulatory sites in Jak2: Ser523 and Tyr570. Inactivation of the repeat 1 domain increased Jak2 basal activity, suggesting that it modulates the kinase activity of the C-terminal catalytic (repeat 2) domain. The Jak2 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",