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bioRxiv · 10.1101/2025.04.02.646541

Apusomonad rhodopsins, a new family of ultraviolet to blue light absorbing rhodopsin channels

Galindo, L. J.·Takaramoto, S.·Nagata, T.·Rozenberg, A.·Takahashi, H.·Beja, O.·Inoue, K.
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Abstract

Apusomonads are a clade of understudied sediment-dwelling bacterivorous protists sister to Opisthokonta. Recently, apusomonads have been found to show a negative phototactic response to blue light. Here, by screening available apusomonad omics data we found genes of a distinct group of microbial rhodopsins, the ApuRs. ApuRs heterologously expressed in mammalian cells absorbed near-UV/violet or blue light, suggesting that ApuRs could be involved in apusomonads photoavoidance response. Electrophysiological measurements indicate that ApuRs are anion-selective rhodopsin channels which evolved independently of the family of channelrhodopsins widespread in other unicellular eukaryotes. Among the known rhodopsin channels, ApuRs collectively demonstrate the most blue-shifted absorption spectra. In ApuRs, the channel opening is triggered by photoisomerization of the retinal from its all-trans form to 13-cis and 11-cis forms. We found that intracellular proton transfer is involved in channel opening and determined the channels open/close kinetics. These findings expand our understanding of the photobiology of heterotrophic flagellates and showcase the significance of these organisms as a source of new rhodopsin families with unanticipated functions.

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Galindo, L. J., Takaramoto, S., Nagata, T., Rozenberg, A., Takahashi, H., Beja, O., Inoue, K.. 2025-04-03. Apusomonad rhodopsins, a new family of ultraviolet to blue light absorbing rhodopsin channels. https://doi.org/10.1101/2025.04.02.646541

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