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Crystal structure of the unphosphorylated IRAK4 kinase domain Bound to a type I inhibitorCrystal structure of the unphosphorylated IRAK4 kinase domain Bound to a type I inhibitor
Structural highlights
Disease[IRAK4_HUMAN] Defects in IRAK4 are the cause of recurrent isolated invasive pneumococcal disease type 1 (IPD1) [MIM:610799]. Recurrent invasive pneumococcal disease (IPD) is defined as two episodes of IPD occurring at least 1 month apart, whether caused by the same or different serotypes or strains. Recurrent IPD occurs in at least 2% of patients in most series, making IPD the most important known risk factor for subsequent IPD.[1] Defects in IRAK4 are the cause of IRAK4 deficiency (IRAK4D) [MIM:607676]. IRAK4 deficiency causes extracellular pyogenic bacterial and fungal infections in otherwise healthy children.[2] [3] Function[IRAK4_HUMAN] Serine/threonine-protein kinase that plays a critical role in initiating innate immune response against foreign pathogens. Involved in Toll-like receptor (TLR) and IL-1R signaling pathways. Is rapidly recruited by MYD88 to the receptor-signaling complex upon TLR activation to form the Myddosome together with IRAK2. Phosphorylates initially IRAK1, thus stimulating the kinase activity and intensive autophosphorylation of IRAK1. Phosphorylates E3 ubiquitin ligases Pellino proteins (PELI1, PELI2 and PELI3) to promote pellino-mediated polyubiquitination of IRAK1. Then, the ubiquitin-binding domain of IKBKG/NEMO binds to polyubiquitinated IRAK1 bringing together the IRAK1-MAP3K7/TAK1-TRAF6 complex and the NEMO-IKKA-IKKB complex. In turn, MAP3K7/TAK1 activates IKKs (CHUK/IKKA and IKBKB/IKKB) leading to NF-kappa-B nuclear translocation and activation. Alternatively, phosphorylates TIRAP to promote its ubiquitination and subsequent degradation. Phosphorylates NCF1 and regulates NADPH oxidase activation after LPS stimulation suggesting a similar mechanism during microbial infections.[4] [5] [6] [7] [8] [9] [10] Publication Abstract from PubMedInterleukin-1 receptor-associated kinase 4 (IRAK4) is a key player in innate immune and inflammatory responses, performing a critical role in signal transduction downstream of Toll-like receptors and interleukin-1 (IL-1) receptors. Upon ligand binding and via its N-terminal death domain, IRAK4 is recruited to an oligomeric receptor that is proximal to the Myddosome signaling complex, inducing IRAK4 kinase domain dimerization, autophosphorylation, and activation. To date, all known IRAK4 structures are in the active conformation, precluding a good understanding of IRAK4's conformational dynamics. To address this issue, here we first solved three crystal structures of the IRAK4 kinase domain (at </=2.6 A resolution), in its unphosphorylated, inactive state bound to either the ATP analog AMP-PNP or to one of the two small-molecule inhibitors JH-I-25 and JH-I-17. The structures disclosed that although the structure in complex with AMP-PNP is in an "alphaC-out" inactive conformation, those in complex with type I inhibitors assume an active "Asp-Phe-Gly (DFG)-in" and "alphaC-in" conformation. The ability of unphosphorylated IRAK4 to take on variable conformations prompted us to screen for small-molecule inhibitors that bind preferentially to unphosphorylated IRAK4, leading to the identification of ponatinib and HG-12-6. Solving the structures of unphosphorylated IRAK4 in complex with these two inhibitors, we found that they both bind as type II inhibitors with IRAK4 in a "DFG-out" conformation. Collectively, these structures reveal conformational flexibility of unphosphorylated IRAK4 and provide unexpected insights into the potential use of small molecules to modulate IRAK4 activity in cancer, autoimmunity, and inflammation. Conformational flexibility and inhibitor binding to unphosphorylated interleukin-1 receptor-associated kinase 4 (IRAK4).,Wang L, Ferrao R, Li Q, Hatcher JM, Choi HG, Buhrlage SJ, Gray NS, Wu H J Biol Chem. 2019 Mar 22;294(12):4511-4519. doi: 10.1074/jbc.RA118.005428. Epub, 2019 Jan 24. PMID:30679311[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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