Channelrhodopsin-1: A light-gated proton channel in green algae

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