Biophysical Society Thematic Meeting | Bucharest 2026

Biophysics of Membrane Reactions in Brian

Wednesday Speaker Abstracts

FUNCTIONS AND THE PHOTOREACTION DYNAMICS OF NON-CANONICAL RHODOPSINS Keiichi Inoue 1,2 ; 1 The University of Tokyo, Department of Integrated Biociences, Graduate School of Frontier Sciences, Kashiwa, Japan 2 The University of Tokyo, The Institute for Solid State Physics, Kashiwa, Japan Microbial rhodopsins are photoreceptive membrane proteins that utilize an all-trans-retinal chromophore accommodated in a binding pocket within a seven- or eight-transmembrane protein architecture. Upon light reception, microbial rhodopsins exhibit diverse functions, including ion pumping, ion channeling, intracellular signaling, and enzymatic reactions. These proteins have also been applied in optogenetics to regulate neural activity with light, representing a promising technology for visual and auditory regeneration. Recently, novel microbial rhodopsins that bind secondary carotenoid chromophores have been discovered in marine environments (Chazan et al., Nature 2023; Fujiwara et al., Nat. Microbiol. 2025; Marín et al., Commun. Biol. 2025). We revealed that while these carotenoids act as antennae pigments, transferring captured light energy to the retinal chromophore and thereby enhancing ion transport activity. In addition, we found that carotenoids can either accelerate the ion-transport turnover rate or regulate the protonation state in the protein, facilitating intramolecular proton transfer. These results suggest the multifaceted roles of carotenoids in microbial rhodopsins. We have also identified a new class of anion channel rhodopsins from Apusomonads, termed ApuRs, which exhibit absorption of the retinal chromophore in the UV region (Takaramoto et al., PNAS 2025). Mutation analyses revealed that the Schiff-base linkage of the retinal chromophore is deprotonated in these rhodopsins, and that its protonation state can be controlled by amino acid residues near the Schiff base. Notably, the absorption wavelengths of ApuRs are the shortest among all known channelrhodopsins, making them useful for multicolor optogenetics in combination with other rhodopsins and for all-optical applications together with fluorescent probes

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