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The serine protease Omi/HtrA2 regulates apoptosis by binding XIAP through a reaper-like motif.

The inhibitor-of-apoptosis proteins (IAPs) play a critical role in the regulation of apoptosis by binding and inhibiting caspases. Reaper family proteins and Smac/DIABLO use a conserved amino-terminal sequence to bind to IAPs in flies and mammals, respectively, blocking their ability to inhibit caspases and thus promoting apoptosis. Here we have identified the serine protease Omi/HtrA2 as a second mammalian XIAP-binding protein with a Reaper-like motif. This protease autoprocesses to form a protein with amino-terminal homology to Smac/DIABLO and Reaper family proteins. Full-length Omi/HtrA2 is localized to mitochondria but fails to interact with XIAP. Mitochondria also contain processed Omi/HtrA2, which, following apoptotic insult, translocates to the cytosol, where it interacts with XIAP. Overexpression of Omi/HtrA2 sensitizes cells to apoptosis, and its removal by RNA interference reduces cell death. Omi/HtrA2 thus extends the set of mammalian proteins with Reaper-like function that are released from the mitochondria during apoptosis.

Pubmed ID: 11602612


  • Martins LM
  • Iaccarino I
  • Tenev T
  • Gschmeissner S
  • Totty NF
  • Lemoine NR
  • Savopoulos J
  • Gray CW
  • Creasy CL
  • Dingwall C
  • Downward J


The Journal of biological chemistry

Publication Data

January 4, 2002

Associated Grants


Mesh Terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Apoptosis
  • Binding Sites
  • Drosophila Proteins
  • Humans
  • Mitochondria
  • Mitochondrial Proteins
  • Molecular Sequence Data
  • Peptides
  • Proteins
  • Serine Endopeptidases
  • X-Linked Inhibitor of Apoptosis Protein