Caspase-9 (CASP9)

Caspase-9 is a cysteine-aspartic protease enzyme that functions as an initiator caspase, playing a critical role in the intrinsic (mitochondrial) apoptotic pathway. It is activated by the apoptosome complex and subsequently activates downstream effector caspases to execute cell death. Beyond apoptosis, caspase-9 has non-apoptotic roles including regulation of necroptosis, cellular differentiation, innate immune response modulation, and mitochondrial homeostasis. Proper function of caspase-9 is vital for normal central nervous system development. Altered expression or function correlates with disease severity in various pathologies, but direct clinical targeting remains under investigation.

Dimerization on Apaf-1 apoptosome via CARD–CARD interaction, leading to activation of downstream effector caspases.