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HulaChrimson: A Chrimson-like cation channelrhodopsin discovered using freshwater metatranscriptomics from Lake Hula
(Hiroto Takahashi, Shunki Takaramoto, Takashi Nagata, Shai Fainsod, Yoshitaka Kato, Oded Béjà, Keiichi Inoue Biophysics and Physicobiology 22, e220014 (2025), DOI: 10.2142/biophysico.bppb-v22.0014)
HulaChrimson is a cation channelrhodopsin that shares high sequence similarity with the widely used optogenetic tool Chrimson (top left). Despite this similarity, HulaChrimson exhibits a peak absorption at 501 nm, which is as much as 80 nm blue-shifted relative to Chrimson (bottom left). This study demonstrates that the spectral difference arises, at least in part, from amino acid residues surrounding the retinal chromophore and from the deprotonation of the counterion residue (right). Elucidating the absorption mechanism of HulaChrimson provides new insights into a novel wavelength-tuning principle in channelrhodopsins.