Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation

Keiichi Kojima, Yuki Matsutani, Takahiro Yamashita, Masataka Yanagawa, Yasushi Imamoto, Yumiko Yamano, Akimori Wada, Osamu Hisatomi, Kanto Nishikawa, Keisuke Sakurai, Yoshinori Shichida

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Most vertebrate retinas contain a single type of rod for scotopic vision and multiple types of cones for photopic and color vision. The retinas of certain amphibian species uniquely contain two types of rods: red rods, which express rhodopsin, and green rods which express a blue-sensitive cone pigment (M1/SWS2 group). Spontaneous activation of rhodopsin induced by thermal isomerization of the retinal chromophore has been suggested to contribute to the rod's background noise, which limits the visual threshold for scotopic vision. Therefore, rhodopsin must exhibit low thermal isomerization rate compared with cone visual pigments to adapt to scotopic condition. In this study, we determined whether amphibian blue-sensitive cone pigments in green rods exhibit low thermal isomerization rates to act as rhodopsin-like pigments for scotopic vision. Anura blue-sensitive cone pigments exhibit low thermal isomerization rates similar to rhodopsin whereas Urodela pigments exhibit high rates like other vertebrate cone pigments present in cones. Furthermore, by mutational analysis we identified a key amino acid residue, Thr47, that is responsible for the low thermal isomerization rates of Anura blue-sensitive cone pigments. These results strongly suggest that, through this mutation, anurans acquired special blue-sensitive cone pigments in their green rods, which could form the molecular basis for scotopic color vision with normal red rods containing green-sensitive rhodopsin.

Original languageEnglish
Pages (from-to)5437-5442
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number21
Publication statusPublished - May 23 2017
Externally publishedYes


  • Amphibian
  • Color discrimination
  • Molecular evolution
  • Photoreceptor cell
  • Visual pigment

ASJC Scopus subject areas

  • General


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