Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation
Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation
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DOI：
10.1073/pnas.1620010114
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发表时间：
2017-05-23
影响因子：
11.1
通讯作者：
Shichida, Yoshinori
中科院分区：
文献类型：
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作者：
Kojima, Keiichi;Matsutani, Yuki;Shichida, Yoshinori
大多数脊椎动物视网膜包含用于暗视觉的单一类型的视杆和用于明视觉和色觉的多种类型的视锥。某些两栖动物物种的视网膜独特地含有两种类型的视杆：表达视紫红质的红视杆和表达蓝色敏感视锥色素的绿色视杆（M1/SWS 2组）。由视网膜发色团的热异构化诱导的视紫红质的自发激活已被认为有助于杆的背景噪声，其限制了暗视觉的视觉阈值。因此，视紫红质必须表现出较低的热异构化速率，以适应暗视条件。在这项研究中，我们确定是否两栖类蓝色敏感锥色素在绿色杆表现出低的热异构化率作为视紫红质样色素暗视觉。无尾目蓝敏感性视锥色素表现出类似于视紫红质的低热异构化速率，而尾椎色素表现出类似于视锥中存在的其他脊椎动物视锥色素的高速率。此外，通过突变分析，我们确定了一个关键的氨基酸残基，Thr 47，这是负责低热异构化率的无尾目蓝敏感锥色素。这些结果有力地表明，通过这种突变，无尾两栖类获得了特殊的蓝色敏感锥色素的绿色杆，这可能是暗色觉的分子基础与正常的红色杆含有绿色敏感的视紫红质。
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.