Tumour-necrosis factor (TNF) receptor-associated factor 6 (TRAF6) is the only TRAF family member that participates in signal transduction of both the TNF receptor (TNFR) superfamily and the interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) superfamily1,2,3,4,5; it is important for adaptive immunity, innate immunity and bone homeostasis. Here we report crystal structures of TRAF6, alone and in complex with TRAF6-binding peptides from CD40 and TRANCE-R (also known as RANK), members of the TNFR superfamily, to gain insight into the mechanism by which TRAF6 mediates several signalling cascades. A 40° difference in the directions of the bound peptides in TRAF6 and TRAF2 shows that there are marked structural differences between receptor recognition by TRAF6 and other TRAFs. The structural determinant of the petide–TRAF6 interaction reveals a Pro-X-Glu-X-X-(aromatic/acidic residue) TRAF6-binding motif, which is present not only in CD40 and TRANCE-R but also in the three IRAK adapter kinases for IL-1R/TLR signalling. Cell-permeable peptides with the TRAF6-binding motif inhibit TRAF6 signalling, which indicates their potential as therapeutic modulators. Our studies identify a universal mechanism by which TRAF6 regulates several signalling cascades in adaptive immunity, innate immunity and bone homeostasis.
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We thank the structural biology groups at the Memorial Sloan-Kettering Cancer Center for use of the microcalorimeter; Z. Cao for human TRAF6 cDNA; G. Mosialos and E. Kieff for the human GST–CD40ct construct; L. Tong, R. Khayat, Z. Yang and C. Lima for help with diffraction data collection; G. Cheng for discussions; C. Ogata and MacCHESS staff for beamline access and support; T. Burling for maintaining the home X-ray source; V. Burkitt and A. Villa for technical help; and laboratory members of Imgenex for synthesizing the decoy peptides. This work was supported in part by the NIH (Y.C.), an MSTP grant (J.R.A.), start-up funds from the Department of Bioimmunotherapy (B.G.D.) and a Translational Research Grant from the Leukemia and Lymphoma Society (B.G.D.). H.Y. is a postdoctoral fellow from the Revson Foundation. H.W. is a Pew Scholar of biomedical sciences and a Rita Allen Scholar.
The authors declare that they have no competing financial interests.
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Ye, H., Arron, J., Lamothe, B. et al. Distinct molecular mechanism for initiating TRAF6 signalling. Nature 418, 443–447 (2002). https://doi.org/10.1038/nature00888
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