Robust Optogenetic Inhibition with Red-light-sensitive Anion-conducting Channelrhodopsins

Abstract

Channelrhodopsins (ChRs) are light-gated ion channels that are widely used to optically activate or silence electrogenic cells such as neurons. Here, we describe the identification and characterization of a set of anion-conducting ChRs (ACRs) from diverse taxa and representing various branches of the ChR phylogenetic tree. The ACR from Mantoniella squamata (MsACR1) showed high sensitivity to yellow-green light (λmax at 555 nm) and was further engineered for optogenetic applications. A single amino-acid substitution that mimicked red-light sensitive rhodopsins like Chrimson shifted the photosensitivity 20 nm towards red light and accelerated photocurrent kinetics. Hence, it was named red and accelerated ACR, raACR. Both wild-type and mutant are capable optical silencers at low light intensities in mouse neurons in vitro and in vivo, while raACR offers a higher temporal resolution.