Spectral properties and isomerisation path of retinal in C1C2 channelrhodopsin.
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 (1)Bu-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.
Institut für Theoretische Chemie und Computerchemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany. Oliver.Weingart@hhu.de.
I
I
Dokukina
O
O
Weingart
D007536:Isomerism; D008958:Models, Molecular; D011789:Quantum Theory; D012172:Retinaldehyde / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D055672:Static Electricity
D012243:Rhodopsin; D012172:Retinaldehyde