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X-linked inhibitor of apoptosis protein (XIAP) inhibits caspase-3 and -7 in distinct modes

Y Suzuki1, Y Nakabayashi, K Nakata

  • 1Laboratory for Motor System Neurodegeneration, RIKEN-Brain Science Institute, Wako City, Saitama 351-0198, Japan.

The Journal of Biological Chemistry
|May 22, 2001
PubMed

Insights

The X-linked inhibitor of apoptosis protein (XIAP) inhibits caspases differently. XIAP

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Death Regulation

Background:

  • Inhibitor of Apoptosis Proteins (IAP) are key regulators of programmed cell death.
  • X-linked IAP (XIAP) is a potent inhibitor of caspases, crucial executioners of apoptosis.
  • The BIR2 domain of XIAP is known to be sufficient for inhibiting caspases-3 and -7.

Purpose of the Study:

  • To elucidate the distinct mechanisms by which XIAP inhibits caspase-3 and caspase-7.
  • To identify the specific domains of XIAP responsible for differential caspase inhibition.
  • To investigate the role of the linker region and BIR2 domain in XIAP-mediated caspase regulation.

Main Methods:

  • Enzyme kinetics assays to determine inhibition mechanisms (competitive vs. non-competitive).
  • Binding assays to map protein-protein interactions between XIAP domains and caspases.
  • Site-directed mutagenesis of XIAP domains and construction of chimeric caspases.

Main Results:

  • XIAP competitively inhibits caspase-3 via interaction with its active site and the XIAP linker region.
  • XIAP inhibits caspase-7 via a mixed mechanism, involving both the linker region (competitive) and BIR2 domain (non-competitive).
  • Mutating the XIAP linker region impaired caspase-3 inhibition but not caspase-7 inhibition.
  • A chimeric caspase-7/3 construct was inhibited by XIAP using a mixed mechanism, highlighting domain contributions.

Conclusions:

  • The linker region between XIAP's BIR1 and BIR2 domains mediates competitive inhibition of both caspase-3 and -7.
  • The XIAP BIR2 domain contributes to the non-competitive inhibition of caspase-7.
  • XIAP employs distinct domain-specific interactions to differentially regulate caspase activity, impacting cell death pathways.

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