Abstract
One of the basic and unresolved puzzles in the chemistry of vision concerns the natural selection of 11-cis-retinal as the light-sensing chromophore in visual pigments. A detailed computational examination of the structure, stability, energetics, and spectroscopy of 7-cis-, 9-cis-, 11-cis-, and 13-cis-retinal isomers in vertebrate (bovine, monkey) and invertebrate (squid) visual pigments was carried out using a hybrid quantum mechanics/molecular mechanics (QM/MM) method. The results show that the electrostatic interaction between retinal and opsin dominates the natural selection of 11-cis-retinal over other cis isomers in the dark state. In all of the pigments, 9-cis-retinal was found to be only slightly higher in energy than 11-cis-retinal, which provides strong evidence for the presence of 9-cis-rhodopsin in nature. 7-cis-Retinal is suggested to be an "upside-down" version of the all-trans isomer because the structural rearrangements observed for 7-cis-rhodopsin from squid were found to be very similar to those for squid bathorhodopsin. The progressive red shift in the calculated absorption wavelength (λ(max)) (431, 456, 490, and 508 nm for the 7-cis-, 9-cis-, 11-cis-, and 13-cis-retinal isomers) is due to the decrease in bond length alternation of the retinal.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
