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Kinetic, energetic, and mechanical differences between dark-state rhodopsin and opsin
Shiho Kawamura1, Moritz Gerstung, Alejandro T Colozo
1Department of Biosystems Science and Engineering, ETH Zürich, Basel, Switzerland.
The absence of the 11-cis-retinal chromophore in rhodopsin (the visual pigment) makes the opsin protein more mechanically stable and flexible, revealing insights into G-protein-coupled receptor activation. This study used single-molecule force spectroscopy.
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Rhodopsin, a key photoreceptor pigment, initiates vision via its 11-cis-retinal chromophore.
- The chromophore acts as an inverse agonist, maintaining rhodopsin's inactive dark state.
- Opsin, the protein without the chromophore, exhibits basal activity.
Purpose of the Study:
- To investigate the kinetic, energetic, and mechanical differences between dark-state rhodopsin and opsin.
- To understand how the chromophore influences receptor properties.
Main Methods:
- Dynamic single-molecule force spectroscopy was employed.
- Analysis was performed on native retinal membranes from mice.
Main Results:
- Opsin, lacking the chromophore, exhibited increased mechanical rigidity and interaction strengths compared to rhodopsin.
- Opsin showed reduced conformational variability, shorter lifetimes, and lower free energies.
- Opsin demonstrated greater pliability and stabilized alternative structural intermediates.
Conclusions:
- The chromophore significantly impacts rhodopsin's mechanical and energetic properties.
- Observed changes in opsin suggest a common mechanism for G-protein-coupled receptor activation.
- Opsin's distinct properties highlight the chromophore's role in regulating receptor function.
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