Coupled HOOP signature correlates with quantum yield of isorhodopsin and analog pigments.
With a quantum yield of 0.66±0.03 the photoisomerization efficiency of the visual pigment rhodopsin (11-cis⇒all-trans chromophore) is exceptionally high. This is currently explained by coherent coupling of the excited state electronic wavepacket with local vibrational nuclear modes, facilitating efficient cross-over at a conical intersection onto the photoproduct energy surface. The 9-cis counterpart of rhodopsin, dubbed isorhodopsin, has a much lower quantum yield (0.26±0.03), which, however, can be markedly enhanced by modification of the retinal chromophore (7,8-dihydro and 9-cyclopropyl derivatives). The coherent coupling in the excited state is promoted by torsional skeletal and coupled HOOP vibrational modes, in combination with a twisted conformation around the isomerization region. Since such torsion will strongly enhance the infrared intensity of coupled HOOP modes, we investigated FTIR difference spectra of rhodopsin, isorhodopsin and several analog pigments in the spectral range of isolated and coupled HCCH wags. As a result we propose that the coupled HOOP signature in these retinal pigments correlates with the distribution of torsion over counteracting segments in the retinylidene polyene chain. As such the HOOP signature can act as an indicator for the photoisomerization efficiency, and can explain the higher quantum yield of the 7,8-dihydro and 9-cyclopropyl-isorhodopsin analogs.
Department of Biochemistry, 286-Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, NL-6500 HB Nijmegen, The Netherlands. Electronic address: Petra.HM.Bovee-Geurts@radboudumc.nl.
Petra H M
PHM
Bovee-Geurts
Department of Biophysical Organic Chemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, NL-2300 RA Leiden, The Netherlands. Electronic address: lugtenbu@chemleidenuniv.nl.
Johan
J
Lugtenburg
Department of Biochemistry, 286-Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, NL-6500 HB Nijmegen, The Netherlands; Department of Biophysical Organic Chemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, NL-2300 RA Leiden, The Netherlands. Electronic address: wim.degrip@radboudumc.nl.
Willem J
WJ
DeGrip
D000818:Animals; D002417:Cattle; D005136:Eye Proteins / Q000378:metabolism*; D007536:Isomerism; D012160:Retina / Q000378:metabolism; D012168:Retinal Pigments / Q000378:metabolism*; D012172:Retinaldehyde / Q000378:metabolism; D012243:Rhodopsin / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D014732:Vibration
D005136:Eye Proteins; D012168:Retinal Pigments; C042882:isorhodopsin; D012243:Rhodopsin; D012172:Retinaldehyde
Chromophore modification; HOOP vibration; Infrared spectroscopy; Ligand-protein interaction; Photochemistry; Vibrational coherence