Color Vision: The "OH-Site" Rule for Seeing Red and Green

• Authors: Sivakumar Sekharan, Emory University; Kota Katayama, Nagoya Institute of Technology; Hideki Kandori, Nagoya Institute of Technology; Keiji Morokuma, Emory University
• Journal Title: Journal of the American Chemical Society
• Volume: Volume 134, Number 25
• Publisher: American Chemical Society | 2012-06-04, Pages 10706-10712
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1021/ja304820p
• Subjects: Chemistry, General

Abstract

Eyes gather information and color forms an extremely important component of the information, more so in the case of animals to forage and navigate within their immediate environment. By using the ONIOM (QM/MM) method, we report a comprehensive theoretical analysis of the structure and molecular mechanism of spectral tuning of monkey-red and green-sensitive visual pigments. We show that, interaction of retinal with three hydroxyl-bearing amino acids near the β-ionone ring part of the retinal in opsin, A164S, F261Y and A269T, increases the electron delocalization, decreases the BLA of the retinal and leads to variation in the wavelength of maximal absorbance in the red- and green-sensitive visual pigments. Based on the analysis, we propose the “OH-site” rule for seeing red and green. This rule is also shown to account for the spectral shifts obtained from hydroxyl-bearing amino acids near the Schiff base in different visual pigments: at site 292 (A292S, A292Y, and A292T) in bovine and at site 111 (Y111) in squid opsins. Therefore, the OH-site rule is shown to be site-specific and not pigment-specific and thus can be used for tracking spectral shifts in any visual pigment.