High temperature requirement protein A2(HTRA2) is a single-pass membrane protein .It contains 1 PDZ (DHR) domain and belongs to the peptidase S1C family. HtrA2 can be released from the mitochondria during apoptosis and uses its four most N-terminal amino acids to mimic a caspase and be recruited by IAP caspase inhibitors such as XIAP and CIAP1/2. It promotes or induces cell death either by direct binding to and inhibition of BIRC proteins (also called inhibitor of apoptosis proteins, IAPs), leading to an increase in caspase activity, or by a BIRC inhibition-independent, caspase-independent and serine protease activity-dependent mechanism. The protein cleaves THAP5 and promotes its degradation during apoptosis.