Apopain protein and inhibitor. Molecular model of caspase-3, also known as apopain, complexed with an inhibitor. Caspase-3 is a protease, an enzyme that cleaves proteins, that plays a role in apoptosis (programmed cell death). It causes the fragmentation of actin filaments, part of a cell's cytoskeleton, and the inactivation of the DNA repairing enzyme poly(ADP-ribose) polymerase. It also activates other caspases as part of the caspase cascade of apoptosis. Caspase-3 is the predominant caspase involved in Alzheimer's disease, processing the protein that is associated with neurone death.