page_title: Caspase
section_title: Cleavage
hierarchical_section_title: Caspase / Activation of caspases / Cleavage
caption_attribution_description: English: caspase 8 activation
context_page_description: Caspases are a family of protease enzymes playing essential roles in programmed cell death. They are named caspases due to their specific cysteine protease activity – a cysteine in its active site nucleophilically attacks and cleaves a target protein only after an aspartic acid residue. As of 2009, there are 12 confirmed caspases in humans and 10 in mice, carrying out a variety of cellular functions.
  The role of these enzymes in programmed cell death was first identified in 1993, with their functions in apoptosis well characterised. This is a form of programmed cell death, occurring widely during development, and throughout life to maintain cell homeostasis. Activation of caspases ensures that the cellular components are degraded in a controlled manner, carrying out cell death with minimal effect on surrounding tissues.
  Caspases have other identified roles in programmed cell death such as pyroptosis and necroptosis. These forms of cell death are important for protecting an organism from stress signals and pathogenic attack. Caspases also have a role in inflammation, whereby it directly processes pro-inflammatory cytokines such as pro-IL1β.
context_section_description: Once appropriately dimerised, the Caspases cleave at inter domain linker regions, forming a large and small subunit. This cleavage allows the active-site loops to take up a conformation favourable for enzymatic activity.
  Cleavage of Initiator and Executioner caspases occur by different methods outlined in the table below. 
  Initiator caspases auto-proteolytically cleave whereas Executioner caspases are cleaved by initiator caspases. This hierarchy allows an amplifying chain reaction or cascade for degrading cellular components, during controlled cell death.
caption: Inititator Pro-caspases have a prodomain that allows recruitment of other pro-caspases, which subsequently dimerise. Both pro-caspase moleuceules undergo cleavage by autocatalysis. This leads to removal of the prodomain and cleavage of the linker region between the large and small subunit. A heterotetramer is formed
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