Caspase activation and recruitment domain of Caspase-9
Caspase activation and recruitment domain (CARD) similar to that found in caspase-9 (CASP9, MCH6, APAF3), which interacts with the CARD of apoptotic protease-activating factor 1 (APAF-1). Caspases are aspartate-specific cysteine proteases with functions in apoptosis and immune signaling. Initiator caspases are the first to be activated following death- or inflammation-inducing signals. Caspase-9 is the initiator caspase associated with the intrinsic or mitochondrial pathway of apoptosis, induced by many pro-apoptotic signals. Together with APAF-1, it forms the heptameric 'apoptosome' in response to the release of cytochrome c from mitochondria. Activated caspase-9 cleaves and activates downstream effector caspases, like caspase-3, caspase-6, and caspase-7, resulting in apoptosis. In general, CARDs are death domains (DDs) associated with caspases. They are known to be important in the signaling pathways for apoptosis, inflammation and host-defense mechanisms. DDs are protein-protein interaction domains found in a variety of domain architectures. Their common feature is that they form homodimers by self-association or heterodimers by associating with other members of the DD superfamily including PYRIN and DED (Death Effector Domain). They serve as adaptors in signaling pathways and can recruit other proteins into signaling complexes.