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  • Cryo-EM structural analysis...
    Fox, Joanna L; Hughes, Michelle A; Meng, Xin; Sarnowska, Nikola A; Powley, Ian R; Jukes-Jones, Rebekah; Dinsdale, David; Ragan, Timothy J; Fairall, Louise; Schwabe, John W R; Morone, Nobuhiro; Cain, Kelvin; MacFarlane, Marion

    Nature communications, 02/2021, Volume: 12, Issue: 1
    Journal Article

    Regulated cell death is essential in development and cellular homeostasis. Multi-protein platforms, including the Death-Inducing Signaling Complex (DISC), co-ordinate cell fate via a core FADD:Caspase-8 complex and its regulatory partners, such as the cell death inhibitor c-FLIP. Here, using electron microscopy, we visualize full-length procaspase-8 in complex with FADD. Our structural analysis now reveals how the FADD-nucleated tandem death effector domain (tDED) helical filament is required to orientate the procaspase-8 catalytic domains, enabling their activation via anti-parallel dimerization. Strikingly, recruitment of c-FLIP into this complex inhibits Caspase-8 activity by altering tDED triple helix architecture, resulting in steric hindrance of the canonical tDED Type I binding site. This prevents both Caspase-8 catalytic domain assembly and tDED helical filament elongation. Our findings reveal how the plasticity, composition and architecture of the core FADD:Caspase-8 complex critically defines life/death decisions not only via the DISC, but across multiple key signaling platforms including TNF complex II, the ripoptosome, and RIPK1/RIPK3 necrosome.