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12:11
A Rhodopsin Transport Assay by High-Content Imaging Analysis
Published on: January 16, 2019
Glutamic acid 181 is uncharged in dark-adapted visual rhodopsin
Sivakumar Sekharan1, Volker Buss
1Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA. ssekhar@emory.edu
Journal of the American Chemical Society
|November 28, 2008
Summary
The study reveals that the orientation of the dipole moment vector, not charge, is crucial for chromophore-protein interactions in visual Rhodopsin. E181 is uncharged in dark-adapted Rhodopsin, indicating a neutral environment.
Area of Science:
- Biochemistry
- Quantum Chemistry
- Structural Biology
Background:
- Chromophore-protein interactions are vital for visual pigment function.
- The role of specific amino acid residues, like E181, in Rhodopsin's spectral properties is debated.
- Understanding these interactions aids in deciphering visual transduction mechanisms.
Purpose of the Study:
- To investigate the role of E181 charge state and dipole moment orientation in Rhodopsin's chromophore-protein interactions.
- To elucidate the electrostatic environment surrounding E181 in dark-adapted visual Rhodopsin.
- To resolve the contentious issue of E181's contribution to spectral shifts.
Main Methods:
- High-level quantum chemical analysis was employed.
- Calculations included charged and uncharged forms of E181 and a mutant E181Q model.
- The primary counterion E113 (A) was considered in the models.
Main Results:
- Calculated spectral shifts were within +/-10 nm, suggesting charge magnitude is less critical.
- The orientation of the dipole moment vector was identified as the key factor influencing spectral properties.
- E181 was found to exist in an uncharged (protonated) form in dark-adapted visual Rhodopsin.
Conclusions:
- The electrostatic environment of E181 in dark-adapted Rhodopsin is predominantly neutral.
- Dipole moment vector orientation, rather than charge state, governs chromophore-protein interactions in this system.
- This finding clarifies a contentious issue regarding E181's function in visual pigments.
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