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Transient channel-opening in bacteriorhodopsin: an EPR study
T E Thorgeirsson1, W Xiao, L S Brown
1Department of Chemistry, University of California, and Division of Structural Biology, Berkeley, CA, 94720, USA.
Journal of Molecular Biology
|January 7, 1998
Summary
Bacteriorhodopsin (bR) uses conformational changes to switch proton release and uptake. Light-induced EPR spectroscopy revealed transient loop opening in bR, facilitating retinal Schiff base reprotonation.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Protein Dynamics
Background:
- Active ion transport across membranes relies on alternating access mechanisms.
- Bacteriorhodopsin (bR) is a light-driven proton pump that utilizes this mechanism.
- The photocycle of bR involves changes in retinal Schiff base accessibility for proton translocation.
Purpose of the Study:
- To investigate the role of protein conformational changes in the reprotonation switch of bR.
- To understand how bR controls proton release and uptake during its photocycle.
Main Methods:
- Site-directed spin labeling of bR at engineered cysteine residues in cytoplasmic interhelical loops.
- Time-resolved electron paramagnetic resonance (EPR) spectroscopy to monitor light-induced distance changes.
Main Results:
- Light-induced distance increases of approximately 5 Å between spin labels on EF and AB/CD interhelical loops.
- These conformational changes occur transiently during the bR photocycle, between proton release and uptake.
Conclusions:
- The observed transient loop opening in bR acts as a conformational switch.
- This switch likely mediates the change in retinal Schiff base accessibility, directing proton uptake after extracellular release.
Keywords:
Non-programmatic