Apoptosis is a process where cells die in a controlled way. Initiator caspases are proteins that start this process. These initiator caspases are inactive at first,They are monomers,called procaspases. It contains a protease domain in its carboxy-terminal region and a small adaptor binding domain near its amino terminus. When an apoptotic signal triggers, adaptor proteins come into action carrying multiple binding sites for the caspase amino-terminal domain. These adaptor proteins bind to the initiator caspases. Binding to the adaptors results in dimerization. This change leads to a cleavage of a specific site in their protease domains and also activation of the initiator caspases. Each protease domain is then rearranged into a large and small subunit. Executioner caspases are also present as dimer, but they are inactive. The initiator caspases activate the executioner caspases by cleaving it in its protease domain. So executioner caspase dimer undergoes a conformational change And it becomes activated Once active, the executioner caspases cleave a variety of key proteins. This cutting leads to the programmed death of the cell. This is how apoptosis works to keep cells healthy.