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Crystal structure of human phosphorylated IRF-3 bound to CBP
Structural highlights
FunctionIRF3_HUMAN Key transcriptional regulator of type I interferon (IFN)-dependent immune responses and plays a critical role in the innate immune response against DNA and RNA viruses. Regulates the transcription of type I IFN genes (IFN-alpha and IFN-beta) and IFN-stimulated genes (ISG) by binding to an interferon-stimulated response element (ISRE) in their promoters. Acts as a more potent activator of the IFN-beta (IFNB) gene than the IFN-alpha (IFNA) gene and plays a critical role in both the early and late phases of the IFNA/B gene induction. Found in an inactive form in the cytoplasm of uninfected cells and following viral infection, double-stranded RNA (dsRNA), or toll-like receptor (TLR) signaling, becomes phosphorylated by IKBKE and TBK1 kinases. This induces a conformational change, leading to its dimerization and nuclear localization and association with CREB binding protein (CREBBP) to form dsRNA-activated factor 1 (DRAF1), a complex which activates the transcription of the type I IFN and ISG genes. Can activate distinct gene expression programs in macrophages and can induce significant apoptosis in primary macrophages. Publication Abstract from PubMedThe innate immune system is the first line of defense against bacterial and viral infections. The recognition of pathogen-associated molecular patterns by the RIG-I-like receptors, TLRs, and cGAS leads to the induction of IFN-I by activating the transcription factor IRF-3. Although the mechanism of IRF-3 activation has been extensively studied, the structural basis of IRF-3 activation upon phosphorylation is not fully understood. In this study, we determined the crystal structures of phosphorylated human and mouse IRF-3 bound to CREB-binding protein (CBP), which reveal that phosphorylated IRF-3 forms a dimer via pSer(386) (pSer(379) in mouse IRF-3) and a downstream pLxIS motif. Size-exclusion chromatography and cell-based studies show that mutations of key residues interacting with pSer(386) severely impair IRF-3 activation and IFN-beta induction. By contrast, phosphorylation of Ser(396) within the pLxIS motif of human IRF-3 only plays a moderate role in IRF-3 activation. The mouse IRF-3/CBP complex structure reveals that the mechanism of mouse IRF-3 activation is similar but distinct from human IRF-3. These structural and functional studies reveal the detailed mechanism of IRF-3 activation upon phosphorylation. The Structural Basis of IRF-3 Activation upon Phosphorylation.,Jing T, Zhao B, Xu P, Gao X, Chi L, Han H, Sankaran B, Li P J Immunol. 2020 Aug 21. pii: jimmunol.2000026. doi: 10.4049/jimmunol.2000026. PMID:32826280[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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