EMD-35713
Cryo-EM structure of the potassium-selective channelrhodopsin HcKCR1 H225F mutant in lipid nanodisc
EMD-35713
Single-particle2.66 Å
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Map released: 06/09/2023
Last modified: 06/11/2024
Sample Organism:
Hyphochytrium catenoides
Sample: HcKCR1
Fitted models: 8iu0 (Avg. Q-score: 0.636)
Raw data: EMPIAR-11558
Deposition Authors: Tajima S
,
Kim Y,
Nakamura S,
Yamashita K
,
Fukuda M,
Deisseroth K,
Kato HE
Sample: HcKCR1
Fitted models: 8iu0 (Avg. Q-score: 0.636)
Raw data: EMPIAR-11558
Deposition Authors: Tajima S
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Structural basis for ion selectivity in potassium-selective channelrhodopsins.
Tajima S
,
Kim YS,
Fukuda M,
Jo Y
,
Wang PY
,
Paggi JM,
Inoue M,
Byrne EFX,
Kishi KE,
Nakamura S,
Ramakrishnan C,
Takaramoto S
,
Nagata T,
Konno M,
Sugiura M,
Katayama K,
Matsui TE,
Yamashita K
,
Kim S,
Ikeda H,
Kim J,
Kandori H,
Dror RO
,
Inoue K,
Deisseroth K,
Kato HE
(2023) Cell , 186 , 4325 - 4344.e26
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(2023) Cell , 186 , 4325 - 4344.e26
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 Å 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.
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 Å 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.