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Issue 38, 2015
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Spectral properties and isomerisation path of retinal in C1C2 channelrhodopsin

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Abstract

Structure and excited state isomerisation pathway of retinal in the channelrhodopsin chimera C1C2 have been investigated with combined quantum mechanical/molecular mechanical (QM/MM) techniques, applying CD-MS-CASPT2//CASSCF and DFT-MRCI quantum methods. The absorbing S1 state is of 1Bu-like character, and the second excited S2 state is dominated by HOMO–LUMO double excitation with small oscillator strength. Upon photoexcitation and torsion along the reactive C13[double bond, length as m-dash]C14 double bond we observe bond length equalisation and a two-path deactivation mechanism in positive and negative torsion directions. The computed path is barrierless in positive direction while a small barrier exists for the opposite side. Comparative protonation studies suggest a charged glutamate E162 residue, with computed resonance Raman data in valuable agreement with experimental channelrhodopsin-2 data. The two negatively charged counter-ions and a positive lysine residue close to the retinal Schiff base terminus have the largest influence on the chromophore absorption wavelength.

Graphical abstract: Spectral properties and isomerisation path of retinal in C1C2 channelrhodopsin

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Supplementary files

Article information


Submitted
07 May 2015
Accepted
02 Sep 2015
First published
02 Sep 2015

This article is Open Access

Phys. Chem. Chem. Phys., 2015,17, 25142-25150
Article type
Paper
Author version available

Spectral properties and isomerisation path of retinal in C1C2 channelrhodopsin

I. Dokukina and O. Weingart, Phys. Chem. Chem. Phys., 2015, 17, 25142
DOI: 10.1039/C5CP02650D

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