Kojima Keiichi, Yanagawa Masataka, Imamoto Yasushi, Yamano Yumiko, Wada Akimori, Shichida Yoshinori, Yamashita Takahiro
Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan; Faculty of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan.
Cellular Informatics Laboratory, RIKEN Cluster for Pioneering Research, Wako, Japan; Molecular and Cellular Biochemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai, Miyagi, Japan.
J Biol Chem. 2024 Apr;300(4):107175. doi: 10.1016/j.jbc.2024.107175. Epub 2024 Mar 16.
High sensitivity of scotopic vision (vision in dim light conditions) is achieved by the rods' low background noise, which is attributed to a much lower thermal activation rate (k) of rhodopsin compared with cone pigments. Frogs and nocturnal geckos uniquely possess atypical rods containing noncanonical cone pigments that exhibit low k, mimicking rhodopsin. Here, we investigated the convergent mechanism underlying the low k of rhodopsins and noncanonical cone pigments. Our biochemical analysis revealed that the k of canonical cone pigments depends on their absorption maximum (λ). However, rhodopsin and noncanonical cone pigments showed a substantially lower k than predicted from the λ dependency. Given that the λ is inversely proportional to the activation energy of the pigments in the Hinshelwood distribution-based model, our findings suggest that rhodopsin and noncanonical cone pigments have convergently acquired low frequency of spontaneous-activation attempts, including thermal fluctuations of the protein moiety, in the molecular evolutionary processes from canonical cone pigments, which contributes to highly sensitive scotopic vision.
暗视觉（在昏暗光线下的视觉）的高灵敏度是通过视杆细胞的低背景噪声实现的，这归因于视紫红质的热激活率（k）远低于视锥色素。青蛙和夜行性壁虎独特地拥有含有非典型视杆细胞，这些视杆细胞含有非经典视锥色素，其k值较低，类似于视紫红质。在这里，我们研究了视紫红质和非经典视锥色素低k值背后的趋同机制。我们的生化分析表明，经典视锥色素的k值取决于其最大吸收波长（λ）。然而，视紫红质和非经典视锥色素的k值比根据λ依赖性预测的值要低得多。鉴于在基于欣谢尔伍德分布的模型中，λ与色素的活化能成反比，我们的研究结果表明，在从经典视锥色素进行的分子进化过程中，视紫红质和非经典视锥色素在包括蛋白质部分的热波动在内的自发激活尝试中，趋同地获得了低频率，这有助于实现高灵敏度的暗视觉。
