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The proapoptotic protein tBid forms both superficially bound and membrane-inserted oligomers
Sanjeevan Shivakumar1, Martin Kurylowicz2, Nehad Hirmiz2
1Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Biophysical Journal
|May 24, 2014
Summary
Truncated Bid (tBid) protein interactions with lipid bilayers reveal distinct mobility states. Immobile tBid species form higher-order oligomers, suggesting membrane insertion involves protein assembly similar to Bax.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biophysics
Background:
- Bid is a pro-apoptotic activator protein of the Bcl-2 family.
- Bid controls mitochondrial outer membrane permeabilization during apoptosis.
Purpose of the Study:
- Characterize the interaction of fluorescently labeled truncated Bid (tBid) with a mitochondria-like supported lipid bilayer at the single-molecule level.
- Investigate the mobility and oligomerization states of tBid upon membrane interaction.
Main Methods:
- Single-molecule fluorescence microscopy on supported lipid bilayers.
- Confocal imaging to distinguish mobile and immobile tBid species.
- Fluorescence fluctuation techniques to determine protein stoichiometry.
Main Results:
- tBid exhibited a wide range of membrane mobility, from fast diffusion to complete immobilization.
- Observed three states: loosely bound, superficially inserted, and fully inserted tBid.
- Immobile tBid species were predominantly tetramers and higher-order oligomers, unlike mobile species.
Conclusions:
- Membrane insertion of tBid involves an oligomerization process.
- This oligomerization is similar to that observed for Bax during apoptosis.
- tBid's membrane interaction dynamics and assembly are crucial for its apoptotic function.
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