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Spatial organization of bacteriorhodopsin in model membranes. Light-induced mobility changes
Nicoletta Kahya1, Douwe A Wiersma, Bert Poolman
1Ultrafast Laser and Spectroscopy Laboratory, Optical Sciences, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. N.Kahya@chem.rug.nl
The Journal of Biological Chemistry
|August 9, 2002
Summary
Photoactivation of bacteriorhodopsin (a proton pump) causes reversible decreases in its mobility, suggesting light-induced oligomerization. This dynamic behavior is crucial for understanding membrane protein function.
Area of Science:
- Biophysics
- Structural Biology
- Membrane Protein Dynamics
Background:
- Bacteriorhodopsin is a key proton-transporting membrane protein in Halophilic archaea.
- It serves as a model for membrane transporters and G-protein-coupled receptors.
- Previous studies suggested protein oligomerization, but its link to light activation was unclear.
Purpose of the Study:
- To investigate the correlation between bacteriorhodopsin oligomerization and light activation.
- To explore the dynamics of bacteriorhodopsin upon photoactivation in a reconstituted system.
Main Methods:
- Reconstitution of bacteriorhodopsin into giant unilamellar vesicles.
- Fluorescence correlation spectroscopy (FCS) to study protein dynamics.
- Freeze-fracture electron microscopy (FFEM) for structural visualization.
Main Results:
- Photoactivation of bacteriorhodopsin led to a reversible decrease in lateral mobility at low protein concentrations.
- This mobility change occurred on a second timescale and was fully reversible upon returning to the dark-adapted state.
- High protein-to-lipid ratios also induced decreased lateral mobility, similar to photoactivation effects.
- Freeze-fracture electron microscopy supported the interpretation of transient photoinduced oligomerization, with clusters of 2-3 trimers.
Conclusions:
- Light activation induces transient oligomerization of bacteriorhodopsin, affecting its lateral mobility.
- This photoinduced oligomerization is a reversible process crucial for bacteriorhodopsin function.
- The findings provide insights into the dynamic behavior of membrane proteins and their response to light stimuli.