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Updated: Feb 25, 2026

Whole-cell Patch-clamp Recordings for Electrophysiological Determination of Ion Selectivity in Channelrhodopsins
Published on: May 22, 2017
Reaction dynamics of the chimeric channelrhodopsin C1C2
Yusaku Hontani1, Marco Marazzi2,3,4, Katja Stehfest5
1Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
Channelrhodopsin (ChR) photoreaction dynamics reveal two distinct relaxation pathways on the excited state. These findings, utilizing advanced spectroscopy and computational methods, elucidate the complete photocycle of C1C2.
Area of Science:
- Biophysics
- Photochemistry
- Structural Biology
Background:
- Channelrhodopsins (ChRs) are essential optogenetic tools.
- C1C2 is the only ChR with a solved crystal structure, enabling structure-based studies.
Purpose of the Study:
- To investigate the ultrafast photoreaction dynamics of the C1C2 channelrhodopsin.
- To characterize the complete photocycle of C1C2 from picoseconds to seconds.
Main Methods:
- Ultrafast transient absorption and multi-pulse spectroscopy.
- Target analysis and hybrid quantum mechanics/molecular mechanics (QM/MM) calculations.
- Structure-based analysis of C1C2.
Main Results:
- Identified two excited-state relaxation pathways via conical intersections (CI1 and CI2).
- Determined distinct relaxation times (450 fs, 2.0 ps, 11 ps) influenced by the active site's hydrogen-bonding network.
- Reported a photoisomerization quantum yield of 30 ± 3%.
Conclusions:
- The presence of CI2 explains the low photoisomerization quantum yield.
- Structural heterogeneity in the active site contributes to varied relaxation dynamics.
- The complete photocycle of C1C2 has been characterized.
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