Channelrhodopsins (ChRs) are light-sensitive ion channels widely used in optogenetics to precisely control neuronal and cardiac activity. While most ChRs conduct cations non-selectively, a specialized subgroup – potassium-selective channelrhodopsins (KCRs) – preferentially transport K⁺ ions, making them promising tools for hyperpolarizing neurons and silencing action potentials. However, the precise molecular mechanism by which KCRs open in response to light has remained unknown.

A recent study provides detailed structural insights into how KCRs function. Using single-particle cryo-electron microscopy (cryo-EM) and molecular dynamics (MD) simulations, researchers determined high-resolution structures of a slow-cycling mutant (C110A) of Hyphochytrium catenoides KCR1 (HcKCR1) in both its dark (closed) and illuminated (open) states.

The study identified a key molecular switch that controls the channel’s opening. Upon photoisomerization of the retinal chromophore, the retinylidene Schiff base (RSB) reorients, triggering a cascade of side-chain rearrangements that merge internal cavities into a continuous transmembrane potassium conduction pathway. Computational modeling confirmed potassium flux through the illuminated state, but not in the resting state.

To validate these findings, the researchers performed structure-guided mutagenesis and electrophysiological measurements using manual as well as automated patch clamp (SyncroPatch 384) combined with the Optogenetic Stimulation Tool. This approach identified Asp105 and Asp116 as critical residues for K⁺ conductance, confirming their essential role in channel gating.

These findings refine our understanding of light-gated ion selectivity and establish a structural basis for engineering advanced optogenetic tools with improved precision for neuroscience and cardiac research.

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Find the full article here: Structural insights into light-gating of potassium-selective channelrhodopsin

Learn more about automated patch clamp here: https://www.nanion.de/product-categories/automated-patch-clamp/ and the Optogenetic Stimulation Tool here: https://www.nanion.de/wp-content/uploads/2024/02/2024_Nanion_Flyer_SyncroPatch-384_Optogenetic-Stimulation-Tool.pdf