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Catalytic domain of the Serine/Threonine kinases, Interleukin-1 Receptor Associated Kinases and related STKs 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. Some IRAKs may also play roles in T- and B-cell signaling, and adaptive immunity. 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. IRAK-1, -2, and -4 are ubiquitously expressed and are active kinases, while IRAK-M is only induced in monocytes and macrophages and is an inactive kinase. Variations in IRAK genes are linked to diverse diseases including infection, sepsis, cancer, and autoimmune diseases. IRAKs contain an N-terminal Death domain (DD), a proST region (rich in serines, prolines, and threonines), a central kinase domain (a pseudokinase domain in the case of IRAK3), and a C-terminal domain; IRAK-4 lacks the C-terminal domain. This subfamily includes plant receptor-like kinases (RLKs) including Arabidopsis thaliana BAK1 and CLAVATA1 (CLV1). BAK1 functions in BR (brassinosteroid)-regulated plant development and in pathways involved in plant resistance to pathogen infection and herbivore attack. CLV1, directly binds small signaling peptides, CLAVATA3 (CLV3) and CLAVATA3/EMBRYO SURROUNDING REGI0N (CLE), to restrict stem cell proliferation: the CLV3-CLV1-WUS (WUSCHEL) module influences stem cell maintenance in the shoot apical meristem, and the CLE40 (CLAVATA3/EMBRYO SURROUNDING REGION40) -ACR4 (CRINKLY4) -CLV1- WOX5 (WUSCHEL-RELATED HOMEOBOX5) module at the root apical meristem. The IRAK 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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