小柯机器人

日本东京大学Hideaki E. Kato和美国斯坦福大学Karl Deisseroth共同合作，近期取得重要工作进展。他们研究发现了钾选择性通道视紫红质离子选择性的结构基础。相关研究成果2023年8月30日在线发表于《细胞》杂志上。

据介绍，KCR通道视紫红质（K⁺选择性光门控离子通道）作为潜在的抑制性光遗传学工具受到了关注，但它们的K⁺选择性是如何实现的目前还不清楚。

研究人员展示了HcKCR1和HcKCR2的2.5–2.7Å冷冻电镜结构，以及具有增强K⁺选择性的结构引导突变体的结构。结构、电生理、计算、光谱和生化分析揭示了K⁺选择性的独特机制，不是形成典型K⁺通道的对称过滤器，实现选择性和脱水，而是在每个单体内的三个细胞外前庭残基形成一个灵活的不对称选择性门，且一个独特的脱水途径延伸到细胞内。结构比较揭示了诱导视网膜旋转的视网膜结合口袋（解释了HcKCR1/HcKCR2光谱差异），并且设计具有增加的K⁺选择性的相应KCR变体（KALI-1/KALI-2）为体外和体内的光遗传学抑制提供了关键优势。

因此，离子通道K⁺选择性机制的发现也为下一代光遗传学提供了框架。

附：英文原文

Title: Structural basis for ion selectivity in potassium-selective channelrhodopsins

Author: Seiya Tajima, Yoon Seok Kim, Masahiro Fukuda, YoungJu Jo, Peter Y. Wang, Joseph M. Paggi, Masatoshi Inoue, Eamon F.X. Byrne, Koichiro E. Kishi, Seiwa Nakamura, Charu Ramakrishnan, Shunki Takaramoto, Takashi Nagata, Masae Konno, Masahiro Sugiura, Kota Katayama, Toshiki E. Matsui, Keitaro Yamashita, Suhyang Kim, Hisako Ikeda, Jaeah Kim, Hideki Kandori, Ron O. Dror, Keiichi Inoue, Karl Deisseroth, Hideaki E. Kato

Issue&Volume: 2023-08-30

Abstract: KCR channelrhodopsins (K+-selective light-gated ion channels) have received attention as potential inhibitory optogenetic tools but more broadly pose a fundamental mystery regarding how their K+ selectivity is achieved. Here, we present 2.5–2.7 cryo-electron microscopy structures of HcKCR1 and HcKCR2 and of a structure-guided mutant with enhanced K+ selectivity. Structural, electrophysiological, computational, spectroscopic, and biochemical analyses reveal a distinctive mechanism for K+ selectivity; rather than forming the symmetrical filter of canonical K+ channels achieving both selectivity and dehydration, instead, three extracellular-vestibule residues within each monomer form a flexible asymmetric selectivity gate, while a distinct dehydration pathway extends intracellularly. Structural comparisons reveal a retinal-binding pocket that induces retinal rotation (accounting for HcKCR1/HcKCR2 spectral differences), and design of corresponding KCR variants with increased K+ selectivity (KALI-1/KALI-2) provides key advantages for optogenetic inhibition in vitro and in vivo. Thus, discovery of a mechanism for ion-channel K+ selectivity also provides a framework for next-generation optogenetics.

DOI: 10.1016/j.cell.2023.08.009

Source: https://www.cell.com/cell/fulltext/S0092-8674(23)00863-2