A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis.
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.
Mesh Terms:
Amino Acid Motifs, Amino Acid Sequence, Animals, Apoptosis, Apoptotic Protease-Activating Factor 1, Carrier Proteins, Caspase 9, Caspases, Catalysis, Cloning, Molecular, Crystallography, X-Ray, Drosophila, Enzyme Activation, Enzyme Inhibitors, Escherichia coli, Humans, Intracellular Signaling Peptides and Proteins, Mitochondrial Proteins, Models, Molecular, Molecular Sequence Data, Protein Binding, Protein Conformation, Protein Processing, Post-Translational, Proteins, Recombinant Proteins, X-Linked Inhibitor of Apoptosis Protein
Amino Acid Motifs, Amino Acid Sequence, Animals, Apoptosis, Apoptotic Protease-Activating Factor 1, Carrier Proteins, Caspase 9, Caspases, Catalysis, Cloning, Molecular, Crystallography, X-Ray, Drosophila, Enzyme Activation, Enzyme Inhibitors, Escherichia coli, Humans, Intracellular Signaling Peptides and Proteins, Mitochondrial Proteins, Models, Molecular, Molecular Sequence Data, Protein Binding, Protein Conformation, Protein Processing, Post-Translational, Proteins, Recombinant Proteins, X-Linked Inhibitor of Apoptosis Protein
Nature
Date: Mar. 01, 2001
PubMed ID: 11242052
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