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Channel Rhodopsins

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Most organisms use photoreceptors to sense and respond to light. Examples of photoreceptors include bacteriorhodopsins and bacteriophytochromes in some bacteria, phytochromes in plants, and rhodopsins in the photoreceptor cells of the vertebral retina. The light-sensitive property of these receptors is because of the bound chromophores, such as bilin in the phytochromes and retinal in the rhodopsins.
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Related Experiment Video

Updated: Dec 17, 2025

Strategic Screening and Characterization of the Visual GPCR-mini-G Protein Signaling Complex for Successful Crystallization

Strategic Screening and Characterization of the Visual GPCR-mini-G Protein Signaling Complex for Successful Crystallization

Published on: March 16, 2020

Activation of the G-Protein-Coupled Receptor Rhodopsin by Water.

Udeep Chawla¹, Suchithranga M D C Perera¹, Steven D E Fried¹

¹Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, 85721, USA.

Angewandte Chemie (International Ed. in English)

|June 30, 2020

Summary

Light absorption causes visual rhodopsin to swell with water, activating the photoreceptor. This hydration change is crucial for visual signal amplification and G-protein signaling.

Keywords:

GPCRs membrane lipids membrane proteins osmotic stress rhodopsin

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Area of Science:

Biochemistry
Molecular Biology
Biophysics

Background:

Visual rhodopsin is a key G-protein-coupled receptor (GPCR) involved in cellular signal transduction.
GPCRs are critical membrane proteins for various biological processes.

Purpose of the Study:

To investigate the role of water molecules in rhodopsin activation and signaling.
To elucidate the mechanism of visual signal amplification.

Main Methods:

Experimental force-based measurements (osmotic and hydrostatic pressure).
Molecular dynamics (MD) simulations.
Analysis of rhodopsin's active state (metarhodopsin-II).

Main Results:

Light absorption causes approximately 80 water molecules to flood rhodopsin, forming a solvent-swollen active state.
Water influx is essential for photoreceptor activation.
Rhodopsin expansion is linked to cavity volume changes and increased hydration in the active state.
Transducin C-terminal helix binding/release is coupled to hydration changes.

Conclusions:

Hydration-dehydration dynamics drive rhodopsin signaling via an allosteric mechanism.
Membrane components like lipids and water play a vital role in the G-protein catalytic cycle.
This mechanism provides insight into visual signal amplification and GPCR function.