DOI: 10.1101/503706Dec 21, 2018Paper

A unifying photocycle model for light adaptation and temporal evolution of cation conductance in Channelrhodopsin-2

BioRxiv : the Preprint Server for Biology
Jens KuhneKlaus Gerwert


Although Channelrhodopsin (ChR) is a widely applied light-activated ion channel, important properties such as light-adaptation, photocurrent inactivation, and alteration of the ion selectivity during continuous illumination are not well-understood from a molecular perspective. Herein, we address these open questions using single turn-over electrophysiology, time-resolved step-scan FTIR and Raman spectroscopy of fully dark adapted ChR2. This yields a unifying parallel photocycle model explaining all data: in dark-adapted ChR2, the protonated Schiff base retinal chromophore (RSBH+) adopts an all-trans,C=N-anti conformation only. Upon light activation, a branching reaction into either a 13-cis,C=N-anti or a 13-cis,C=N-syn retinal conformation occurs. The anti-cycle features sequential H+ and Na+ conductance in a late M-like state and an N-like open-channel state. In contrast, the 13-cis,C=N-syn isomer represents a second closed-channel state identical to the long lived P480-state, which has been previously assigned to a late intermediate in a single photocycle model. Light excitation of P480 induces a parallel syn-photocycle with an open channel state of small conductance and high proton selectivity. E90 becomes deprotonated in P4...Continue Reading

Related Concepts

Electrophysiology (Science)
Biological Evolution
Proton Pump
Ion Channel
Spectrum Analysis, Raman
Spectroscopy, Fourier Transform Infrared
Light Adaptation

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