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Retinal-Carotenoid Interactions in a Sodium-Ion-Pumping Rhodopsin: Implications on Oligomerization and Thermal
Mihir Ghosh1, Ramprasad Misra1, Sudeshna Bhattacharya1
1Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 76100, Israel.
The Journal of Physical Chemistry. B
|March 1, 2023
Summary
Microbial rhodopsins like DDR2 can bind carotenoids, forming stable light-harvesting complexes. The carotenoid salinixanthin enhances DDR2
Area of Science:
- Biochemistry and Biophysics
- Microbiology
- Photochemistry
Background:
- Microbial rhodopsins are light-harvesting complexes, but their interactions with carotenoids are not fully understood.
- Few rhodopsins are known to bind carotenoids, limiting knowledge of their properties.
Purpose of the Study:
- To investigate the interaction between a novel sodium-ion pumping microbial rhodopsin, DDR2, and the carotenoid salinixanthin (Sal).
- To characterize the thermal stability and oligomerization of the DDR2-Sal complex.
Main Methods:
- Spectroscopic studies (UV-Vis, CD) to monitor retinal-carotenoid interactions and thermal stability.
- Size-exclusion chromatography (SEC) and homology modeling to analyze protein oligomerization.
- Thermal denaturation assays to assess pigment stability at different temperatures, pH, and concentrations.
Main Results:
- DDR2 forms a thermally stable complex with salinixanthin.
- DDR2 exists mainly as a pentamer at room temperature and neutral pH, with partial conversion to a less stable oligomeric form upon heating above 55 °C.
- Salinixanthin significantly enhances the thermal stability of DDR2, maintaining pigment integrity up to 85 °C.
Conclusions:
- The DDR2-Sal complex is a naturally occurring, thermally stable rhodopsin-carotenoid conjugate.
- Salinixanthin binding increases the thermal stability of DDR2, suggesting potential applications in designing robust light-harvesting antenna systems.
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