Cryo-EM structural analysis of FADD:Caspase-8 complexes defines the catalytic dimer architecture for co-ordinated control of cell fate

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