HcKCR2 corresponds to the light-gated, potassium ion-conducting kalium channelrhodopsin (KCR) encoded by the Hyphochytrium catenoides KCR2 gene. It can be used as an optogenetic tool to produce membrane hyperpolarization and inhibit neuron activity; the peak activation wavelength is 490nm under continuous one-photon illumination. The formation of a functional channel requires the presence of a covalently linked all-trans-retinal chromophore which can be provided exogenously if necessary via the culture medium or diet (this cofactor is present endogenously in some intact vertebrate systems). For detailed kinetic and spectral properties, see PMID:35726059.