Structures of Channelrhodopsin Paralogs in Peptidiscs Explain Their Contrasting K+ and Na+ Selectivities

Authors

Takefumi Morizumi
Kyumhyuk Kim
Hai Li
Elena G Govorunova
Oleg A Sineshchekov
Yumei Wang
Lei Zheng
Éva Bertalan
Ana-Nicoleta Bondar
Azam Askari
Leonid S Brown
John L Spudich
Oliver P Ernst

Publication Date

7-20-2023

Journal

Nature Communications

Abstract

Kalium channelrhodopsin 1 from Hyphochytrium catenoides (HcKCR1) is a light-gated channel used for optogenetic silencing of mammalian neurons. It selects K+ over Na+ in the absence of the canonical tetrameric K+ selectivity filter found universally in voltage- and ligand-gated channels. The genome of H. catenoides also encodes a highly homologous cation channelrhodopsin (HcCCR), a Na+ channel with >100-fold larger Na+ to K+ permeability ratio. Here, we use cryo-electron microscopy to determine atomic structures of these two channels embedded in peptidiscs to elucidate structural foundations of their dramatically different cation selectivity. Together with structure-guided mutagenesis, we show that K+ versus Na+ selectivity is determined at two distinct sites on the putative ion conduction pathway: in a patch of critical residues in the intracellular segment (Leu69/Phe69, Ile73/Ser73 and Asp116) and within a cluster of aromatic residues in the extracellular segment (primarily, Trp102 and Tyr222). The two filters are on the opposite sides of the photoactive site involved in channel gating.

Keywords

Animals, Channelrhodopsins, Cryoelectron Microscopy, Cations, Mammals