Archaerhodopsin variants with enhanced voltage-sensitive fluorescence in mammalian and Caenorhabditis elegans neurons.

Nicholas C Flytzanis, Claire N Bedbrook, Hui Chiu, Martin K M Engqvist, Cheng Xiao, Ken Y Chan, Paul W Sternberg, Frances H Arnold, Viviana Gradinaru

Index: Nat. Commun. 5 , 4894, (2014)

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Abstract

Probing the neural circuit dynamics underlying behaviour would benefit greatly from improved genetically encoded voltage indicators. The proton pump Archaerhodopsin-3 (Arch), an optogenetic tool commonly used for neuronal inhibition, has been shown to emit voltage-sensitive fluorescence. Here we report two Arch variants with enhanced radiance (Archers) that in response to 655 nm light have 3-5 times increased fluorescence and 55-99 times reduced photocurrents compared with Arch WT. The most fluorescent variant, Archer1, has 25-40% fluorescence change in response to action potentials while using 9 times lower light intensity compared with other Arch-based voltage sensors. Archer1 is capable of wavelength-specific functionality as a voltage sensor under red light and as an inhibitory actuator under green light. As a proof-of-concept for the application of Arch-based sensors in vivo, we show fluorescence voltage sensing in behaving Caenorhabditis elegans. Archer1's characteristics contribute to the goal of all-optical detection and modulation of activity in neuronal networks in vivo.