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Conformation of membrane-associated proapoptotic tBid
Xiao-Min Gong1, Jungyuen Choi, Carla M Franzin
1Burnham Institute, La Jolla, California 92037, USA.
The Journal of Biological Chemistry
|May 5, 2004
Summary
The Bcl-2 family protein tBid adopts a unique helical conformation in lipid membranes. This structure, determined by NMR, explains how tBid induces cell death by destabilizing mitochondrial membranes.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- The Bcl-2 family protein Bid is a key regulator of apoptosis.
- Cleavage by caspase-8 generates the active fragment tBid.
- tBid translocates to mitochondria, inducing cytochrome c release and cell death.
Purpose of the Study:
- To characterize the conformation of tBid in lipid membrane environments.
- To elucidate the mechanism of tBid-induced mitochondrial outer membrane permeabilization.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy (solution and solid-state).
- Circular Dichroism (CD) spectroscopy.
- Lipid micelle and lipid bilayer model systems.
Main Results:
- In micelles, tBid adopts a unique helical conformation with well-resolved NMR resonances.
- In lipid bilayers, tBid associates parallel to the membrane surface, without trans-membrane insertion.
- Solid-state NMR confirms NH bonds are parallel to the bilayer surface, indicating surface association.
Conclusions:
- tBid's helical conformation on the mitochondrial membrane surface is crucial for its proapoptotic activity.
- This mechanism may resemble that of antibiotic polypeptides destabilizing bacterial membranes.
- tBid likely induces cell death by promoting leakage through bilayer destabilization.