Color Shifted Channelrhodopsins- Towards Red Light Optogenetics

Abstract

Channelrhodopsins (ChRs) are microbial type rhodopsins functioning aslight-sensitive cation channels in microalgae. Since channelrhodopsinsdepolarize membranes in the light, they are used as optogenetic tools for generating action potentials in neurons by blue light flashes.Recently we identified two channelrhodopsin variants in the colonial alga Volvox carteri. One of them named Volvox Channelrhodopsin 1 (VChR1) shows a red shifted action spectra with an absorption maximum at 548 nm. Although there is strong demand for a red-absorbing channelrhodopsin, application of VChR1 has been very limited due to its low expression level in neurons. Now we report about the expression of hybrids comprising fragments of VChR1, VChR2 and Chlamydomonas ChR2 with improved expression level. In addition we identified residues involved in color-tuning. Our goal is to provide ChR variants that in total cover the complete visible spectrum all the way from 400 to 600 nm.