Three Families of Channelrhodopsins and Their Use in Optogenetics (review)

Abstract

Channelrhodopsins are retinylidene proteins unique in their ability to generate light-gated passive ion currents across the membrane. Heterologous expression of channelrhodopsins in animal cells, most notably, neurons, enables precise millisecond-scale control of their activity (optogenetics). For 15 years only cation-conducting channelrhodopsins derived from chlorophyte (green) algae have been known, which now are widely used in neuroscience research to stimulate neurons with light. Recently a distinct family of channelrhodopsins with strictly anion selectivity has been discovered in phylogenetically distant cryptophyte flagellate algae. Furthermore, the genomes of the latter microorganisms also encode a structurally distinct group of rhodopsins capable of cation channel activity using different molecular mechanisms as compared to their chlorophyte counterparts. In this review, we mostly focus on the two latest additions and their utility for optogenetic applications.