Programmed cell death via apoptosis is a key controlled physiological process instigated by the cell death receptor family, their ligands, and the caspase cysteine protease family. All caspases exist in a precursor form that contains a prodomain, and large and small catalytic subunits. A cleavage event adjacent to an aspartate liberates one large and one small subunit, which are now free to associate into an active a2b2 tetramer. Caspases are activated by triggers such as ligand-receptor interactions, growth factor deprivation, and cell function inhibitors.
