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Membrane perturbations induced by the apoptotic Bax protein
Raquel F Epand1, Jean-Claude Martinou, Sylvie Montessuit
1Department of Biochemistry, McMaster University Health Sciences Centre, Hamilton, ON L8N 3Z5, Canada. epand@mcmaster.ca
The Biochemical Journal
|August 16, 2002
Summary
Oligomeric Bax protein effectively permeabilizes liposomes, especially with calcium. Its activity depends on oligomeric state and membrane binding, which is enhanced by oligomerization and calcium.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- The apoptotic protein Bax plays a crucial role in programmed cell death.
- Bax's function is regulated by its oligomeric state and interactions with lipid membranes.
Purpose of the Study:
- To investigate the role of Bax oligomerization in membrane permeabilization.
- To understand the influence of calcium and tBid on Bax activity.
- To determine the stability and membrane translocation properties of oligomeric Bax.
Main Methods:
- Liposome-based assays to measure leakage and lipid mixing.
- Use of bis-ANS to assess hydrophobic site exposure.
- Energy-transfer assay to measure membrane translocation.
- Varying detergent concentrations to study Bax stability.
Main Results:
- Oligomeric Bax, but not monomeric Bax, induces liposome leakage and lipid mixing, enhanced by calcium.
- Caspase-8-cut Bid (tBid) augments leakage caused by monomeric Bax at low concentrations.
- Oligomeric Bax retains activity upon dilution but loses potency and membrane translocation ability in low detergent without liposomes.
- Membrane binding and translocation are significantly enhanced by Bax oligomerization and the presence of calcium.
Conclusions:
- The membrane-active form of Bax is unstable without detergent or lipid.
- Bax oligomerization and calcium are critical for efficient membrane binding and translocation.
- These findings elucidate the mechanism of Bax-mediated membrane permeabilization during apoptosis.