The eNpHR(Unk) entry in FlyBase represents an engineered light-gated chloride pump that can be used as an optogenetic tool to induce membrane hyperpolarization and inhibit neuron activity, where the tool is based on the naturally occurring light-gated chloride pump encoded by the Natronomonas pharaonis NpHR gene (UniProtKB:P15647), but where the precise variant is unknown/unspecified. Typically, the coding sequence also contains a signal peptide and may include other trafficking signals. 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).