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Multiple photocycles of channelrhodopsin
Peter Hegemann1, Sabine Ehlenbeck, Dietrich Gradmann
1Experimentelle Biophysik, Fachbereich für Biologie, Humboldt-Universität zu Berlin, 10115 Berlin, Germany. hegemann@rz.hu-berlin.de
Biophysical Journal
|September 20, 2005
Summary
Two light-gated ion channels, channelrhodopsins (ChR1 and ChR2) from Chlamydomonas reinhardtii, were characterized. ChR1 exhibits a light-induced proton conductance, while ChR2 conducts various cations.
Area of Science:
- Biophysics
- Molecular Biology
- Photobiology
Background:
- Channelrhodopsins (ChR1 and ChR2) are light-gated ion channels identified in Chlamydomonas reinhardtii.
- These rhodopsins possess intrinsic ion conductance properties.
Purpose of the Study:
- To characterize the ion conductance properties of ChR1 and ChR2.
- To quantitatively analyze the light-induced conductance kinetics of ChR1.
- To develop a reaction scheme describing ChR1 photocurrent kinetics.
Main Methods:
- Expression of ChR1 and ChR2 in Xenopus laevis oocytes.
- Two-electrode voltage clamp electrophysiology to study ion channel activity.
- Quantitative analysis of light-induced conductance and photocurrent kinetics.
Main Results:
- ChR1 is a proton-specific channel, while ChR2 conducts Na+, K+, Ca2+, and guanidinium.
- ChR2 shows a light-induced peak and steady-state conductance, with altered kinetics at high pH.
- ChR1 exhibits a light-induced peak conductance at high intensities, contrary to previous reports.
- A quantitative reaction scheme for ChR1 involving two dark states (D1, D2) and two conducting states (M1, M2) was developed.
Conclusions:
- ChR1 and ChR2 represent distinct types of light-gated ion channels with different ion selectivities and kinetic properties.
- The study provides a detailed kinetic model for ChR1, elucidating its photoactivation and deactivation mechanisms.
- These findings contribute to understanding the function and diversity of microbial rhodopsins.