The interaction between PmHtrA2 and PmIAP and its effect on the activity of Pm caspase

• The role of PmHtrA2 in apoptosis is observed through protein interaction study with PmIAP.
• The interaction between PmIAP and PmHtrA2 is mediated by the BIR2 domain from PmIAP.
• The BIR2 domain of PmIAP can inhibit Pm caspase.
• The inhibition of Pm caspase by the BIR2 can be blocked by IBM motif from PmHtrA2.

Apoptosis is an essential mechanism in multicellular organisms which results in the induction of cell death. Important apoptotic proteins, including high temperature requirement A2 (PmHtrA2; also known as serine protease), inhibitor of apoptosis protein (PmIAP) and Pm caspase, have been previously identified in black tiger shrimp, Penaeus monodon. However, the relevance among these proteins in apoptosis regulation has not been established yet in shrimp. Here, we showed that PmHtrA2 was able to interact with PmIAP and the binding of the two proteins was mediated by the BIR2 domain of PmIAP. In addition, the BIR2 of PmIAP was shown to be able to inhibit Pm caspase activity. The inhibitory effect of the BIR2 domain on Pm caspase was impaired under the presence of the IBM peptide of PmHtrA2, implying a role for PmHtrA2 in apoptosis activation. Our combined results suggested that P. monodon possesses a conserved mechanism by which the caspase-3 activity is modulated by HtrA2 and IAP, as previously seen in insects and mammals.