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The Fas–FADD death domain complex structure unravels signalling by receptor clustering


The death inducing signalling complex (DISC) formed by Fas receptor, FADD (Fas-associated death domain protein) and caspase 8 is a pivotal trigger of apoptosis1,2,3. The Fas–FADD DISC represents a receptor platform, which once assembled initiates the induction of programmed cell death. A highly oligomeric network of homotypic protein interactions comprised of the death domains of Fas and FADD is at the centre of DISC formation4,5. Thus, characterizing the mechanistic basis for the Fas–FADD interaction is crucial for understanding DISC signalling but has remained unclear largely because of a lack of structural data. We have successfully formed and isolated the human Fas–FADD death domain complex and report the 2.7 Å crystal structure. The complex shows a tetrameric arrangement of four FADD death domains bound to four Fas death domains. We show that an opening of the Fas death domain exposes the FADD binding site and simultaneously generates a Fas–Fas bridge. The result is a regulatory Fas–FADD complex bridge governed by weak protein–protein interactions revealing a model where the complex itself functions as a mechanistic switch. This switch prevents accidental DISC assembly, yet allows for highly processive DISC formation and clustering upon a sufficient stimulus. In addition to depicting a previously unknown mode of death domain interactions, these results further uncover a mechanism for receptor signalling solely by oligomerization and clustering events.

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Figure 1: Overall structure of the Fas–FADD death domain complex.
Figure 2: Fas–FADD death domain complex: Fas–FADD and Fas–Fas interactions are dependent on Fas opening.
Figure 3: The Fas–FADD bridge in the DISC: binding of full-length FADD and the key role of Fas opening in vivo.
Figure 4: Model of DISC formation: mechanism of receptor signalling through clustering.

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We thank S. Snipas for protein sequencing and technical assistance, J. Reed for providing Fas cDNA and A. Bobkov for the AUC. This work was supported by a P30 CA030199 cancer center grant and R01AA017238 to S.J.R.; PO1CA69381 to G.S.S.; and MCEXT-033534 to R.S. Data measured at beamline X29 of the National Synchrotron Light Source were also supported by Biological and Environmental Research DOE, and National Center for Research Resources NIH. Earlier stages of the work were supported by a LLS scholarship to S.J.R. S.J.R. is currently a V Foundation scholar.

Author Contributions F.L.S. performed and evaluated in vivo studies. J.J.L. and M.K.D. performed cloning, protein expression and crystallization. C.P. performed biochemical analyses. H.R., B.S. and in particular R.S. performed data collection and structure solution. E.M. performed EM-studies. G.S.S. participated in study design and evaluation. All authors discussed the work. S.J.R. participated in and oversaw all aspects of the work and wrote the manuscript.

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Correspondence to Robert Schwarzenbacher or Stefan J. Riedl.

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Atomic coordinates and experimental structure factors have been deposited within the Protein Data Bank and are accessible under the code 3EZQ.

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This file contains Supplementary Figures 1-5, a Supplementary Discussion, Supplementary Tables 1-2, Supplementary Methods and Supplementary References (PDF 1797 kb)

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Scott, F., Stec, B., Pop, C. et al. The Fas–FADD death domain complex structure unravels signalling by receptor clustering. Nature 457, 1019–1022 (2009).

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