A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis

Nature. 2001 Mar 1;410(6824):112-6. doi: 10.1038/35065125.

Abstract

X-linked inhibitor-of-apoptosis protein (XIAP) interacts with caspase-9 and inhibits its activity, whereas Smac (also known as DIABLO) relieves this inhibition through interaction with XIAP. Here we show that XIAP associates with the active caspase-9-Apaf-1 holoenzyme complex through binding to the amino terminus of the linker peptide on the small subunit of caspase-9, which becomes exposed after proteolytic processing of procaspase-9 at Asp315. Supporting this observation, point mutations that abrogate the proteolytic processing but not the catalytic activity of caspase-9, or deletion of the linker peptide, prevented caspase-9 association with XIAP and its concomitant inhibition. We note that the N-terminal four residues of caspase-9 linker peptide share significant homology with the N-terminal tetra-peptide in mature Smac and in the Drosophila proteins Hid/Grim/Reaper, defining a conserved class of IAP-binding motifs. Consistent with this finding, binding of the caspase-9 linker peptide and Smac to the BIR3 domain of XIAP is mutually exclusive, suggesting that Smac potentiates caspase-9 activity by disrupting the interaction of the linker peptide of caspase-9 with BIR3. Our studies reveal a mechanism in which binding to the BIR3 domain by two conserved peptides, one from Smac and the other one from caspase-9, has opposing effects on caspase activity and apoptosis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Apoptosis Regulatory Proteins
  • Apoptosis*
  • Apoptotic Protease-Activating Factor 1
  • Carrier Proteins / metabolism*
  • Caspase 9
  • Caspase Inhibitors
  • Caspases / metabolism*
  • Catalysis
  • Cloning, Molecular
  • Crystallography, X-Ray
  • Drosophila
  • Enzyme Activation
  • Enzyme Inhibitors / metabolism
  • Escherichia coli
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Mitochondrial Proteins*
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Conformation
  • Protein Processing, Post-Translational
  • Proteins / chemistry
  • Proteins / metabolism*
  • Recombinant Proteins / metabolism
  • X-Linked Inhibitor of Apoptosis Protein

Substances

  • APAF1 protein, human
  • Apoptosis Regulatory Proteins
  • Apoptotic Protease-Activating Factor 1
  • Carrier Proteins
  • Caspase Inhibitors
  • DIABLO protein, human
  • Enzyme Inhibitors
  • Intracellular Signaling Peptides and Proteins
  • Mitochondrial Proteins
  • Proteins
  • Recombinant Proteins
  • X-Linked Inhibitor of Apoptosis Protein
  • XIAP protein, human
  • CASP9 protein, human
  • Caspase 9
  • Caspases