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Contribution of membrane elastic energy to rhodopsin function
Olivier Soubias1, Walter E Teague, Kirk G Hines
1Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland, USA.
Biophysical Journal
|August 5, 2010
Summary
Lipid composition affects the metarhodopsin I (MI) to metarhodopsin II (MII) equilibrium. Membrane elastic stress and specific lipid-protein interactions, like hydrogen bonding, both influence this crucial visual protein transition.
Area of Science:
- Biophysics
- Membrane protein dynamics
- Spectroscopy
Background:
- The metarhodopsin I (MI) to metarhodopsin II (MII) transition is critical for visual signal transduction.
- Understanding how lipid composition influences this transition is key to comprehending visual photochemistry.
Purpose of the Study:
- To investigate whether shifts in the MI-MII equilibrium are solely explained by membrane bilayer curvature elastic stress.
- To explore the roles of specific lipid properties and headgroup interactions in modulating the MI-MII equilibrium.
Main Methods:
- Flash photolysis coupled with UV-vis spectroscopy to monitor the MI-MII equilibrium.
- (2)H NMR order parameter profiling to determine membrane properties like area-per-lipid and hydrophobic thickness.
- Systematic variation of lipid composition using a series of ethanolamines and POPC.
Main Results:
- Shifts in the MI-MII equilibrium correlated with membrane elastic properties for some lipids.
- Elastic energy alone only partially explained the observed shifts in the MI-MII equilibrium.
- Hydrogen bonding capabilities of ethanolamine headgroups and specific fatty acid chain compositions also significantly impacted the equilibrium.
Conclusions:
- Both membrane elastic stress and specific lipid-protein interactions contribute to the MI-MII equilibrium shifts.
- The first layer of lipids surrounding rhodopsin plays a significant role, alongside broader membrane properties.
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