H-bond network around retinal regulates the evolution of ultraviolet and violet vision

• Authors: Ahmet Altun, Emory University; Keiji Morokuma, Emory University; Shozo Yokoyama, Emory University
• Journal Title: ACS Chemical Biology
• Volume: Volume 6, Number 8
• Publisher: American Chemical Society | 2011-08-19, Pages 775-780
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1021/cb200100f
• Subjects: Chemistry, Biochemistry; Chemistry, General

Abstract

Ancestors of vertebrates used ultraviolet vision. Some descendants preserved ultraviolet vision while some others replaced it with violet vision, and then, some of avian lineages reinvented ultraviolet vision. Ultraviolet (absorption at ~360 nm) and violet (410–440 nm) sensitivities of visual pigments are known to be affected by around 20 amino acid substitutions. The present quantum mechanical/molecular mechanical calculations show that these substitutions modify a H-bond network formed by two waters and sites 86, 90, 113, 114, 118 and 295, which determines the protonation state of Schiff base-linked 11-cis-retinal. A pigment is ultraviolet-sensitive when it is more stable with an unprotonated retinal (SBR) form than with its protonated analog (PSBR), and is violet-sensitive when the PSBR form is more stable. These results establish for the first time the chemical basis of ultraviolet and violet vision in vertebrates.