Apoptosome cell death protein, molecular model. Apoptosomes are large protein structures formed during programmed cell death (PCD, also called apoptosis). They play a critical role in triggering the cascade of biochemical reactions that cause the death of a cell. This is an octomeric (eight-part) assembly of the apoptosome CED-4, from the nematode roundworm Caenorhabditis elegans. The eight components (shown here in different colours) form this funnel shape.