XIAP
XIAP (X-linked inhibitor of apoptosis protein) is an inhibitor-of-apoptosis protein that binds and directly inhibits active caspases, at the final step of the death program.
Function
XIAP’s baculoviral IAP repeat (BIR) domains bind caspase-3, caspase-7 and caspase-9: the BIR2 linker region occupies the active site of the executioner caspases, and BIR3 dimerizes and inactivates caspase-9. Its RING domain acts as an E3 ubiquitin ligase that tags bound caspases and its own regulators for degradation. Because caspase-3 cleaves XIAP during apoptosis, the inhibitor and its target form a mutual-destruction loop that helps make the death program irreversible once caspase activity passes a threshold.
In cancer
Tumors overexpressing
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