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Updated: Jun 4, 2026
12:11
A Rhodopsin Transport Assay by High-Content Imaging Analysis
Published on: January 16, 2019
His75-Asp97 cluster in green proteorhodopsin.
Franziska Hempelmann1, Soraya Hölper, Mirka-Kristin Verhoefen
1Institute of Biophysical Chemistry & Centre for Biomolecular Magnetic Resonance, Goethe-University Frankfurt, Frankfurt, Germany.
Journal of the American Chemical Society
|March 4, 2011
Summary
Proteorhodopsin
Area of Science:
- Biochemistry
- Microbiology
- Spectroscopy
Background:
- Proteorhodopsins (PR) are abundant in marine bacteria.
- PR variants are color-tuned to their environment.
- A conserved histidine at position 75 (His75) is unique to PR.
Purpose of the Study:
- Investigate the role of His75 in proteorhodopsin function.
- Determine the structural and dynamic properties of His75.
- Clarify the impact of His75 on the PR photocycle.
Main Methods:
- Solid-state NMR spectroscopy ((13)C and (15)N MAS NMR) to probe structure.
- Site-directed mutagenesis to alter His75.
- Time-resolved optical spectroscopy (vis-pump/vis-probe, flash photolysis) to study dynamics.
Main Results:
- His75 forms a pH-dependent hydrogen bond with Asp97, explaining its high pK(a).
- Mutating His75 (PR(H75N)) retains primary reaction dynamics but accelerates the photocycle.
- A pH-dependent His-Asp cluster is identified, potentially common in eubacterial retinal proteins.
Conclusions:
- His75 stabilizes the PR structure but slows the photocycle.
- PR is not optimized for rapid proton transfer, questioning its in vivo function.
- The His-Asp cluster's role in eubacterial retinal proteins warrants further investigation.
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