Takahashi Hiroto, Takaramoto Shunki, Nagata Takashi, Fainsod Shai, Kato Yoshitaka, Béjà Oded, Inoue Keiichi
The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
Faculty of Biology, Technion-Israel Institute of Technology, Haifa 3200003, Israel.
Biophys Physicobiol. 2025 Jul 5;22(3):e220014. doi: 10.2142/biophysico.bppb-v22.0014. eCollection 2025.
Chrimson is cation-conducting channelrhodopsin (CCR) with the most red-shifted absorption spectrum, rendering itself as one of the most promising optogenetic tools. However, the molecular mechanisms underlying its red-shifted absorption have not been completely clarified yet. Here, we found a CCR gene showing high sequence similarity to Chrimson from Lake Hula through freshwater metatranscriptome sampling. Interestingly, despite its high similarity to Chrimson, this CCR-named HulaChrimson-showed significantly blue-shifted action and absorption spectra compared to those of Chrimson. Mutations of amino acid residues, which are prominently different from those in Chrimson, in HulaChrimson did not reproduce the red-shifted absorption of Chrimson, suggesting the color-tuning between these proteins achieved by organizing the entire protein architecture, particularly in the broad hydrogen bonding network around the retinal Schiff base counterion, rather than by the difference in several specific residues. The optical characteristics of HulaChrimson distinct from those of Chrimson provide a basis for understanding the color-tuning mechanisms of channelrhodopsins.
深红视蛋白是一种阳离子传导通道视紫红质（CCR），其吸收光谱具有最大程度的红移，这使其成为最有前景的光遗传学工具之一。然而，其红移吸收背后的分子机制尚未完全阐明。在这里，我们通过淡水宏转录组采样，从胡拉湖发现了一个与深红视蛋白具有高度序列相似性的CCR基因。有趣的是，尽管该CCR（命名为胡拉深红视蛋白）与深红视蛋白高度相似，但其作用光谱和吸收光谱与深红视蛋白相比却有明显的蓝移。胡拉深红视蛋白中与深红视蛋白显著不同的氨基酸残基突变，并未重现深红视蛋白的红移吸收，这表明这些蛋白质之间的颜色调谐是通过构建整个蛋白质结构实现的，特别是通过围绕视黄醛席夫碱抗衡离子的广泛氢键网络，而不是通过几个特定残基的差异。胡拉深红视蛋白与深红视蛋白不同的光学特性为理解通道视紫红质的颜色调谐机制提供了基础。
