KALI1 corresponds to the light-gated, potassium ion-conducting kalium channelrhodopsin (KCR) encoded by the Hyphochytrium catenoides KCR1 gene, into which a H225F amino acid substitution has been introduced (this improves K[+] selectivity). It can be used as an optogenetic tool to induce membrane hyperpolarization and inhibit neuron activity. 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:37652010.