Autocatalytic processing of HtrA2/Omi is essential for induction of caspase-dependent cell death through antagonizing XIAP |
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Authors: | Seong Young-Mo Choi Ju-Youn Park Hyo-Jin Kim Ki-Joong Ahn Sang-Gun Seong Geun-Hye Kim In-Kyung Kang Seongman Rhim Hyangshuk |
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Institution: | Graduate School of Biotechnology, Korea University, Seoul 136-701, Korea. |
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Abstract: | A mature form of nuclear-encoded mitochondrial serine protease HtrA2/Omi is pivotal in regulating apoptotic cell death; however, the underlying mechanism of the processing event of HtrA2/Omi and its relevant biological function remain to be clarified. Here, we describe that HtrA2/Omi is autocatalytically processed to the 36-kDa protein fragment, which is required for the cytochrome c-dependent caspase activation along with neutralizing XIAP-mediated inhibition of caspases through interaction with XIAP, eventually promoting apoptotic cell death. We have shown that the autocatalytic processing of HtrA2/Omi occurs via an intermolecular event, demonstrated by incubating an in vitro translated HtrA2/Omi (S306A) mutant with the enzymatically active glutathione S-transferase-HtrA2/Omi protein. Using N-terminal amino acid sequencing and mutational analysis, we identified that the autocatalytic cleavage site is the carboxyl side of alanine 133 of HtrA2/Omi, resulting in exposure of an inhibitor of apoptosis protein binding motif in its N terminus. Our study provides evidence that the autocatalytic processing of HtrA2/Omi is crucial for regulating HtrA2/Omi-mediated apoptotic cell death. |
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