MSc Exit Seminar- Yan Ling Iris Chiu (Chang Lab)

Functional characterization and molecular evolutionary analyses of dim-light adaptations in visual pigments and interactions with arrestin 

Abstract:

The visual system of dim-light dwelling/nocturnal species are known be to highly adaptive due to the importance of vision for survival. Rhodopsin and cone opsins are responsible for dim-light and colour vision, respectively, and mediate photon absorption which results in isomerization of the retinal chromophore and activation of the visual pigment. This triggers the downstream visual transduction cascade which is subsequently inhibited by the binding of the signaling protein arrestin. Here, I investigated different aspects of dim-light adaptation using a combination of computational and experimental approaches. The first study investigated arrestin-rhodopsin complex formation relevant to a hypothesized photoprotection mechanism in dim-light vertebrates. Putatively adaptive mutations from dim-light animals identified in comparative analyses were found to enhance the ability of arrestin-rhodopsin complexes to sequester toxic retinal chromophore when experimentally assayed in vitro. The second study analyzed the selective pressures across the visual pigment gene RH2 of teleost fishes and found a positively selected site with unusual amino acid substitutions in the deep-sea northern lampfish. When assayed experimentally, substitutions at this site showed altered kinetics, with implications for better photosensitivity and cold adaptation. Overall, my findings provide insight into the less-well studied aspects of dim-light adaptation and show the significance of investigating the visual system as an interdisciplinary study involving evolution, biochemistry and molecular biology.