Proteins FADD Fas-associated death domain

An important trigger for apoptosis is known as the Fas system. This is used by cytotoxic Tcells, for example, which eliminate infected cells in this way (top left). Most of the body s cells have Fas receptors (CD 95) on their plasma membrane. If a T cell is activated by contact with an MHC presenting a viral peptide (see p. 296), binding of its Fas ligands occurs on the target cell s Fas receptors. Via the mediator protein FADD ( Fas-associated death domain ), this activates cas-pase-8 inside the cell, setting in motion the apoptotic process. 

Death domain receptors. The cytokine TNF (tumor necrosis factor) uses a type of receptor called the death domain receptor (Fig. 11.21). These receptors function as a trimer when they bind TNF (which is also a trimer). On TNF binding, an inhibitory protein called the silencer of death is released from the receptor. The receptor then binds and activates several adaptor proteins. One adaptor protein, FADD (fas-associated death domain), recruits and activates the zymogen form of a proteolytic enzyme called caspase. Caspases... 

Apoptosis can be induced by two pathways the extrinsic pathway starts with an activation of death receptors on the cell surface, which leads to the activation of caspases (Figure 5). Death receptors are a subgroup of the tumor necrosis factor (TNF) receptor family that have an intracellular death domain. Death receptors include CD95, TRAIL-Rl, and TRAIL-R2 (TNF-related apoptosis inducing ligand). The stimulated death receptors activate an adaptor protein FADD (Fas-associated death domain protein), which, in turn, activates the inactive form of caspase-8 (cysteine-aspartyl-specific proteases). Caspase-8 activates pro-caspase-3 and also the protein Bid (a member of the Bcl-2 family) that can stimulate and amplify the intrinsic pathway. 

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