Autocatalytic processing of HtrA2/Omi is essential for induction of caspase-dependent cell death through antagonizing XIAP.
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.
Seong
Young-Mo
YM
Graduate School of Biotechnology, Korea University, Seoul 136-701, Korea.
Choi
Ju-Youn
JY
Park
Hyo-Jin
HJ
Kim
Ki-Joong
KJ
Ahn
Sang-Gun
SG
Seong
Geun-Hye
GH
Kim
In-Kyung
IK
Kang
Seongman
S
Rhim
Hyangshuk
H
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D020169:Caspases / Q000378:metabolism*; D002384:Catalysis; D002460:Cell Line; D004789:Enzyme Activation; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000378:metabolism*; D051636:X-Linked Inhibitor of Apoptosis Protein
D024101:Mitochondrial Proteins; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; D020169:Caspases