eNpHR2.0 is an engineered light-gated chloride pump that can be used as an optogenetic tool to induce membrane hyperpolarization and inhibit neuron activity. eNpHR2.0 was generated by adding an N-terminal signal peptide (from the β subunit of nAChR) and a C-terminal endoplasmic reticulum export signal (FCYENEV from Kir2.1) to the naturally occurring light-gated chloride pump encoded by the Natronomonas pharaonis NpHR gene (UniProtKB:P15647). These changes prevent the formation of aggregates that are seen when high levels of NpHR are expressed (PMID:18677566). 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 a comparison of eNpHR2.0 and other neuron inhibition tools, see PMID:21415127 and PMID:21745635.