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Mechanisms of opsin activation
J Buczyłko1, J C Saari, R K Crouch
1Department of Ophthalmology, School of Medicine, University of Washington, Seattle, Washington 98195, USA.
The Journal of Biological Chemistry
|August 23, 1996
Summary
Rhodopsin activation can occur without light by adding retinal analogues to opsin, forming non-covalent complexes. Protonation of opsin
Area of Science:
- Biochemistry
- Molecular Biology
- Photochemistry
Background:
- Rhodopsin, a G protein-coupled receptor, mediates vision.
- Its activation involves light-induced isomerization of 11-cis-retinal.
- This triggers conformational changes leading to metarhodopsin II b formation.
Purpose of the Study:
- To investigate rhodopsin activation independent of light.
- To explore the role of retinal analogues in opsin activation.
- To elucidate the structural requirements for receptor activation.
Main Methods:
- Activation of opsin using various all-trans-retinal analogues.
- Measurement of opsin phosphorylation by rhodopsin kinase.
- pH titrations to assess receptor conformation.
Main Results:
- Opsin activation was achieved using all-trans-retinal and its analogues without illumination.
- Potency varied with analogue structure, isomer, and polyene chain length.
- Activation resulted from non-covalent complexes, not Schiff base formation.
- Protonation of cytoplasmic carboxyl groups in opsin is crucial for activity.
Conclusions:
- Opsin activation can be triggered by non-covalent interactions with retinoids.
- A model suggests protonation of opsin carboxyl groups is essential for activity.
- This provides insights into rhodopsin activation mechanisms and mutant functions.