Probing human red cone opsin activity with retinal analogues
Masahiro Kono1, Rosalie K Crouch
1Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina 29425, United States. konom@musc.edu
Journal of Natural Products
|February 15, 2011
Summary
Retinal analogues reveal that red cone opsin can be deactivated without a covalent bond. Red cone opsin shows distinct activation patterns compared to rhodopsin, suggesting a more open binding pocket.
Area of Science:
- Biochemistry
- Molecular Biology
- Vision Science
Background:
- Retinal analogues are crucial for studying visual pigment function, particularly rhodopsin.
- Direct extrapolation of rhodopsin findings to cone visual pigments is not always valid due to protein differences.
Purpose of the Study:
- To investigate the effects of various retinal analogues on human red cone opsin's interaction with transducin.
- To determine the structural requirements for red cone opsin activation and deactivation.
Main Methods:
- Synthesis and application of full-length and truncated retinal analogues.
- Assay of transducin activation by human red cone opsin in the presence of analogues.
- Comparative analysis of analogue effects on red cone opsin versus rhodopsin.
Main Results:
- Beta-ionone confirmed that covalent bonding is not essential for red cone opsin deactivation.
- Several small compounds effectively deactivated the red cone opsin.
- Trans-configured polyene chain extension beyond 9 carbons resulted in agonism, up to all-trans-retinal.
- The all-trans-C17 analogue was an agonist, while the 9-cis-C17 analogue acted as an inverse agonist, differing from rhodopsin behavior.
- A 22-carbon analogue showed no agonist or inverse agonist activity.
Conclusions:
- Human red cone opsin can be deactivated by non-covalent interactions.
- Red cone opsin exhibits unique activation/deactivation properties compared to rhodopsin.
- These findings suggest a more flexible and less selective chromophore-binding pocket in red cone opsin than in rhodopsin.
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