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Catalytic domain of the Serine/Threonine kinase, Interleukin-1 Receptor Associated Kinase 4 STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. IRAKs are involved in Toll-like receptor (TLR) and interleukin-1 (IL-1) signalling pathways, and are thus critical in regulating innate immune responses and inflammation. IRAKs contain an N-terminal Death domain (DD), a proST region (rich in serines, prolines, and threonines), a central kinase domain, and a C-terminal domain; IRAK-4 lacks the C-terminal domain. Vertebrates contain four IRAKs (IRAK-1, -2, -3 (or -M), and -4) that display distinct functions and patterns of expression and subcellular distribution, and can differentially mediate TLR signaling. IRAK4 plays a critical role in NFkB activation by its interaction with MyD88, which acts as a scaffold that enables IRAK4 to phosphorylate and activate IRAK1 and/or IRAK2. It also plays an important role in type I IFN production induced by TLR7/8/9. The IRAK4 subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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