Apaf-1 apoptotic protease-activating factor

In cytosol, cytochrome c combines with very high affinity with a cytosolic protein called Apoptotic Protease-Activating Factor 1 (Apaf-1) and dATP. The complex, in turn, combines with an inactive protease precursor, procaspase 9, to form the apoptosome . As a result, several procaspase 9 molecules are placed near each other, and they cleave each other to form active caspases 9. When formed, caspase 9 attacks procaspase 3 and cleaves it to form active caspase 3, a protease that hydrolyses certain enzymes occupying key positions on the metabolic map. This causes cell death. 

Novel pathways include apoptotic protease-activating factor-1 (APAF-1) with an N-terminal caspase recruitment domain (CARD) recruiting caspase-9, or the RIP-like kinase CARDIAK specifically interacting with the CARD of caspase-1 (Thome et al., 1998). The overall structure of the... 

Interestingly, evidence has been obtained that Fas may induce apoptosis via different pathways that are used almost exclusively in different cells (Scaffidi et al. 1998). In some cells. Fas ligation induced a rapid and strong activation of caspase-8 and caspase-3 (see above and Fig. 1) and subsequent apoptosis was not blocked by Bcl-2. In other cells, Fas-ligation resulted in a considerably weaker activation of FLICE (caspase-8), which cleaves Bid, a proapoptotic member of the Bcl-2 family (Luo et al. 1998 Li et al. 1998). Cleaved Bid subsequently translocates to mitochondria, where it promotes, either alone or together with Bax, cytochrome c efflux (Eskes et al. 2000). Subsequently, cytochrome c can interact with the cytosolic apoptotic protease-activating factor 1 (Apaf-1), which in turn activates caspase 9... 

Binds pro-apoptotic protease activating factor (Apaf-1)... 

It is now well estahlished that activation of the caspase cascade is an indispensable and sufficient process in the execution phase of apoptosis (Nunez et al, 1998). As for mitochondria-mediated apoptosis, cytochrome c released from the mitochondrial inner membrane is well known to play an important role in the activation of caspase 9, one of the upstream proteases in the cascade (Zou et al, 1997). For activation of caspase 9, cytochrome c or apoptotic protease activating factor 2 (Apaf 2) induces the formation of the complex between Apaf 1 and caspase 9. The resultant activated caspase 9 then activates caspase 3, which in turn leads to the genomic DNA fragmentation and apoptotic cell death. 

Apaf-1 Apoptotic protease-activating factor APAF1... 

Analyte A substance or chemical that is detected by an analytical procedure. Antigen A molecule that elicits an immune response (i.e., antibody production). Apaf-1 Apoptotic protease activating factor 1 a cytosolic protein that forms part... 

In the cytosol, cytochrome c binds Apaf (pro-apoptotic protease activating factor). The Apaf/cytochrome c complex binds caspase 9, an initiator caspase, to form an active complex called the apoptosome. The apoptosome in turn activates execution caspases by zymogen cleavage. 

Cytochrome c (Cyt c), the peripheral protein loosely associated with the inner membrane of mitochondria, is one of the most well-known factors involved in apoptosis (Green 2005). In healthy cells, Cyt c functions as an electron shuttle in the respiratory chain and its activity is necessary for life. Cyt c is released by the mitochondria as the consequence of elevated permeability of the outer membrane in responses to proapoptotic stimuli (Li et al. 1997). In the cytosol, Cyt c binds to the apoptosis-protease activating factor 1 (Apaf-1), which then recruits caspase-9 to form the apoptosome (Li et al. 1997). Caspase-9 in turn cleaves and activates executioner caspase-3, resulting in apoptotic cell death as described above. The whole process requires energy and relatively intact cell machinery. 

Cytochrome c release is thus an early event during apoptosis, occurring hours before phosphatidylserine exposure and loss of plasma membrane integrity. As mentioned above, it is only after cytochrome c release that caspases areactivated and the cell undergoes apoptosis. The actual apoptotic process occurs through the formation of an apoptosome (comprised of cytochrome c, apoptosis protease activating factor 1 (Apaf-1) and procaspase-9). This apoptosome then recruits procaspase-3, which is cleaved and activated by the active caspase-9 and is subsequently released to mediate apoptosis (Fig. 2) [27]. 

The extrinsic pathway involves binding of specific death ligands to their respective cell surface receptors, such as Fas, tumor necrosis factor alpha (TNF-a) receptor, and TRAIL and activates downstream signaling pathways via adapter molecules. Adapter molecules subsequently recruit and initiate cysteine protease (e.g., caspase-8) which, in turn, cleaves downstream effector caspases, such as caspase-9 and caspase-3, leading to the activation of DNA degradation. The intrinsic pathway is dependent on the release of cytochrome c from the mitochondria and other pro-apoptotic molecules, Smac/DIABLO, into the cytoplasm. Its association with Apaf 1 activates caspase-9 and caspase-3 to trigger apoptosis (Olson and Garban 2008). 

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