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Updated: Apr 17, 2026

Electromechanical Assessment of Optogenetically Modulated Cardiomyocyte Activity
Published on: March 5, 2020
Converting a light-driven proton pump into a light-gated proton channel.
Keiichi Inoue1, Takashi Tsukamoto, Kazumi Shimono
1Department of Frontier Materials, Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555, Japan.
Modifying archaerhodopsin-3 (AR3) created AR3-T, a light-gated proton channel. This reveals that key functional differences in proton transporters reside in the membrane-spanning domain.
Area of Science:
- Membrane biophysics
- Protein engineering
- Ion transport mechanisms
Background:
- Ion pumps and channels are crucial membrane proteins with distinct functions.
- Archaerhodopsin-3 (AR3) and channelrhodopsin (ChR) share structural similarity but differ in function.
- Differences in retinal binding cavities suggest structural variations influencing function.
Purpose of the Study:
- To investigate how structural modifications in AR3 affect its ion transport function.
- To determine the location of functional determinants in proton transporters.
- To engineer a proton pump to exhibit channel activity.
Main Methods:
- Site-directed mutagenesis to create AR3-T by altering residues around the retinal.
- Electrophysiological recordings to assess ion flux and membrane potential.
- Spectroscopic analysis to characterize photochemical properties and retinal configuration.
Main Results:
- AR3-T exhibited an inward proton (H+) flux, suggesting channel or pump activity.
- Electrophysiology confirmed light-gated ion channeling activity with near-zero reverse membrane potential.
- Spectroscopic data showed AR3-T shares photochemical properties with ChRs, including retinal configuration and Schiff base interactions.
Conclusions:
- The functional determinant for proton transport activity is localized within the membrane-spanning domain of AR3.
- Structural modifications in the retinal binding pocket can switch pump activity to channel activity.
- This study highlights the plasticity of ion transport proteins and the importance of the central membrane domain.
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