Abstract

H. catenoides kalium channelrhodopsins (HcKCR1 and HcKCR2) are potassium-selective light-gated ion channels with unique properties for optogenetics. Here we report cryo-electron microscopy (cryo-EM) structures of HcKCR1 and HcKCR2 with endogenous retinal. Strikingly, one structure of HcKCR1 represents the conducting state with continuous potassium ion flow in the lumen, while another in non-conducting state with discontinuous potassium ion flow. Further electrophysiological studies identified extracellular side of ion permeation region as the major element for channel potassium selectivity and retinal binding region for channel gating. Our results uncover the unprecedented potassium selectivity and light-gating mechanism, and may facilitate the rational design of new optogenetic tools.