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Caspase-9 and APAF-1 form an active holoenzyme
1Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724 USA.
Abstract:
Autocatalytic activation of initiator caspases is the link between pro-apoptotic signals and the destruction machinery of apoptosis. Activation of caspase-9, which mediates oncogene and drug-induced apoptosis, requires binding to the protein APAF-1. We found that the proteolytic activity of caspase-9 in a complex with APAF-1 is several orders of magnitude higher than that of the free enzyme. Thus, this complex functions as a holoenzyme in which caspase-9 is the catalytic subunit and APAF-1 its allosteric regulator. We argue that caspase-9 is activated by allosteric regulation and suggest that this mechanism is common for other initiator caspases.
Insights
Initiator caspases like caspase-9 are activated by allosteric regulation. Binding to APAF-1 dramatically enhances caspase-9
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Autocatalytic activation of initiator caspases links pro-apoptotic signals to apoptosis execution.
- Caspase-9 activation is crucial for oncogene and drug-induced apoptosis.
- Caspase-9 activation requires binding to the protein APAF-1.
Purpose of the Study:
- To investigate the mechanism of caspase-9 activation by APAF-1.
- To determine the role of the caspase-9/APAF-1 complex in apoptosis.
Main Methods:
- Biochemical assays to measure proteolytic activity.
- Protein complex formation studies.
Main Results:
- The caspase-9/APAF-1 complex exhibits proteolytic activity several orders of magnitude higher than free caspase-9.
- APAF-1 acts as an allosteric regulator for caspase-9, forming a holoenzyme.
Conclusions:
- Caspase-9 activation is mediated by allosteric regulation through APAF-1.
- The caspase-9/APAF-1 complex functions as an active holoenzyme.
- Allosteric activation may be a common mechanism for initiator caspase activation.