Related Experiment Videos
Cation Binding to Xanthorhodopsin: Electron Paramagnetic Resonance and Magnetic Studies
Elena Smolensky Koganov1, Gregory Leitus1, Rinat Rozin1
1Department of Organic Chemistry and ‡Department of Chemical Research Support, Weizmann Institute of Science , Rehovot 76100, Israel.
The Journal of Physical Chemistry. B
|April 6, 2017
Summary
Xanthorhodopsin (xR), a proton pump, binds divalent cations like Mn2+ and Ca2+. Mn2+ binds cooperatively, forming clusters, while Ca2+ binds with lower affinity, indicating distinct cation interactions.
Area of Science:
- Biochemistry
- Biophysics
- Microbiology
Background:
- Xanthorhodopsin (xR) is a retinal protein functioning as a proton pump in Salinibacter ruber.
- xR possesses a carotenoid for light harvesting, transferring absorbed energy to retinal.
- Previous studies noted spectral changes in xR due to residue protonation.
Purpose of the Study:
- To investigate the cation-binding capabilities of xR.
- To characterize the binding affinity and mechanism of divalent cations (Mn2+, Ca2+) to deionized xR (DI-xR).
Main Methods:
- Electron paramagnetic resonance (EPR) spectroscopy to detect cation binding.
- SQUID magnetometry to study cation interactions.
- Spectroscopic analysis of deionized xR (DI-xR).
Main Results:
- xR binds divalent cations, including Mn2+ and Ca2+.
- Mn2+ exhibits high-affinity binding at one site, followed by cooperative binding of approximately 40 equivalents and weak binding of ~100 equivalents.
- Mn2+ cooperative binding is attributed to cluster formation, distinct from lower-affinity Ca2+ binding.
Conclusions:
- xR demonstrates specific cation-binding properties.
- The distinct binding affinities and cooperative behavior of Mn2+ suggest cluster formation, differentiating it from Ca2+ binding.