IRAK3 (IRAK-M) is a pseudokinase of the IRAK family that acts as a negative feedback regulator of Toll-like receptor and interleukin-1 receptor signaling in myeloid cells. It has an N-terminal death domain, through which IRAK proteins assemble with MyD88 in the receptor-proximal Myddosome, a central kinase-like domain with a noncanonical, catalytically compromised active site and weak ATP affinity, and a C-terminal region. Studies of the mouse and human orthologs show that IRAK-M is induced by TLR stimulation and restrains signaling by preventing release of IRAK1 and IRAK4 from MyD88 and the formation of IRAK1-TRAF6 complexes, which limits inflammatory cytokine production and contributes to endotoxin tolerance. This UniProt entry is an alternative Ensembl gene model of horse IRAK3 that begins at an alternative first exon, lacks the first 50 residues of the canonical 614-residue product (F6QZW8), and keeps most of the death domain and the complete pseudokinase domain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005524 ATP binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: The horse product retains the complete kinase-like domain, and the human ortholog binds ATP with weak affinity in an unobstructed pocket. Nucleotide binding is real but secondary to the scaffolding role of this pseudokinase. Reason: InterPro2GO maps the protein kinase domain to ATP binding. The human IRAK3 pseudokinase domain, in the same PANTHER subfamily (PTHR24419:SF7), binds ATP only weakly but does bind it and binds ATP-competitive inhibitors with high affinity. The horse benchmark model contains the full pseudokinase domain (all 288 residues of the human domain align, 123-410) with the same noncanonical CGS/DFA configuration, so the term is retained. It does not imply phosphotransfer activity and is not the core function, so it is kept as non-core. Supporting Evidence: PMID:33238146 Here, we find that IRAK3 has a weak affinity for ATP, despite having a mostly unobstructed ATP-binding pocket that is accessible for the ATP-competitive inhibitor staurosporine. file:HORSE/IRAK3/IRAK3-bioinformatics/RESULTS-rereview.md | Protein kinase domain 165-452 | 288/288, 123-410 | 288/288, 170-457 | 288/288 | |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MODIFY | Summary: Correct but too general. IRAK3 acts specifically in MyD88-dependent Toll-like receptor and interleukin-1 receptor signaling, the pathways to which PAINT propagates the IRAK3 clade. Reason: The death-domain InterPro2GO mapping gives the generic signal transduction term. The IRAK3 subfamily (PTHR24419:SF7) operates in receptor-proximal TLR/IL-1R signaling. Human IRAK-M reconstitutes the IL-1 response in IRAK1-deficient cells, mouse IRAK-M controls MyD88-associated IRAK complexes, and PAINT places interleukin-1-mediated signaling and lipopolysaccharide-mediated signaling at nodes inherited by IRAK3 (these IBAs are present on the canonical horse product F6QZW8 but are not projected to this alternative model). The benchmark model keeps the Pfam/InterPro death-domain match (64 of 66 residues of the human PROSITE death domain) but lacks the N-terminal 50 residues of the canonical product. The replacement terms describe the gene; whether this particular alternative product assembles into the Myddosome has not been tested. Proposed replacements: MyD88-dependent toll-like receptor signaling pathway interleukin-1-mediated signaling pathway Supporting Evidence: PMID:10383454 Although IRAK-M and IRAK-2 exhibit only a negligible autophosphorylation activity, they can reconstitute the IL-1 response in a 293 mutant cell line lacking IRAK. PMID:12150927 IRAK-M prevented dissociation of IRAK and IRAK-4 from MyD88 and formation of IRAK-TRAF6 complexes. file:HORSE/IRAK3/IRAK3-bioinformatics/RESULTS-rereview.md Benchmark residues 4-567 are an exact substring of F6QZW8 starting at canonical residue 51. |
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Download this section (compressed HTML)Q: Is the alternative first exon used by the horse transcript ENSECAT00000032597 (A0A3Q2HDT6, starting MIT and lacking canonical residues 1-50) supported by horse RNA-seq or CAGE data, or is it a gene-model artifact?
Q: Human IRAK3 Ser110, phosphorylated by IRAK1 and isomerised by PIN1 in the IL-33 pathway, is Asn in horse. Does horse IRAK-M participate in IL-33-driven nuclear signaling by another route, or is that mechanism primate-specific?
Experiment: Express the horse canonical (F6QZW8) and alternative (A0A3Q2HDT6) IRAK3 products in IRAK3-deficient macrophages and compare MyD88 co-immunoprecipitation and suppression of LPS-induced cytokine production, to test whether the 50-residue N-terminal truncation affects Myddosome assembly.
Type: complementation and co-immunoprecipitation
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