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

Abstract

The Death Inducing Signaling Complex (DISC) formed by Fas receptor, FADD and caspase-8 is a pivotal trigger of apoptosis1-3. 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 (DD) of Fas and FADD is at the center of DISC formation4, 5. Thus characterising the mechanistic basis for the Fas/FADD interaction is paramount for understanding DISC signaling but has remained enigmatic largely due to a lack of structural data. We have successfully formed and isolated the Fas/FADD DD complex and here we report the 2.7 Å crystal structure. The complex shows a tetrameric arrangement of four FADD DDs bound to four Fas DDs. We show that an opening of the Fas DD 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 functions as a mechanistic switch. This switch prevents accidental DISC assembly, yet allows for highly processive DISC formation and clustering upon a sufficient stimulus. Thus besides depicting a previously unknown mode of death domain interactions, these results further uncover a mechanism for receptor signaling solely by oligomerization and clustering events.

Parameter-free methods distinguish Wnt pathway models and guide design of experiments

“…Based on injectivity-multistationarity analysis, we find that the shuttle model predicts the possibility of a regulatory switch, acting early in the cell fate determination pathway. Other systems have also reported early checkpoints in cell fate signaling in activation of apoptosis through receptor-ligand binding (51,52). We identify the possibility of important roles for spatial localization and degradation in cell fate switching.…”

FADD cleavage by NK cell granzyme M enhances its self-association to facilitate procaspase-8 recruitment for auto-processing leading to caspase cascade

“…The intracellular DD motif can recruit the DD-containing adaptor protein FADD through homophilic DD/DD interactions. 16,17,31 FADD possesses an N-terminal DED and a C-terminal DD domains, which recruits procaspase-8 to generate the DISC.…”

Regulation of CD95/Fas signaling at the DISC

“…18 Recently, there have been several new reports on the X-ray structure of the complex formed by isolated CD95 and FADD DDs. 19,20 Scott et al 19 have suggested that binding of CD95L leads to an opening of the CD95 DD, which exposes the FADD-binding site and simultaneously generates a bridge between two CD95 molecules. They show that a basic unit of this oligomeric CD95 network is composed of a tetramer, comprising four FADD DDs and four CD95 DDs.…”