Channelrhodopsin-1: A Light-Gated Proton Channel in Green Algae

TLDR

Green algae use rhodopsins with microbial chromophores to mediate phototaxis and photophobic responses, and the hydrophobic core of the identified protein shares homology with the light‑activated proton pump bacteriorhodopsin. We identified a cDNA encoding Channelopsin‑1 in *Chlamydomonas reinhardtii*, and its expression (or just its hydrophobic core) in Xenopus oocytes with all‑trans retinal produced a light‑gated proton conductance, suggesting that Channelrhodopsins participate in algal phototaxis.

Abstract

Phototaxis and photophobic responses of green algae are mediated by rhodopsins with microbial-type chromophores. We report a complementary DNA sequence in the green alga Chlamydomonas reinhardtii that encodes a microbial opsin-related protein, which we term Channelopsin-1. The hydrophobic core region of the protein shows homology to the light-activated proton pump bacteriorhodopsin. Expression of Channelopsin-1, or only the hydrophobic core, in Xenopus laevis oocytes in the presence of all- trans retinal produces a light-gated conductance that shows characteristics of a channel selectively permeable for protons. We suggest that Channelrhodopsins are involved in phototaxis of green algae.