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© The Rockefeller University Press, 0021-9525/2002/7/195-b $5.00
The Journal of Cell Biology, Volume 158, Number 2, July 22, 2002 195-b-195

Let there be a channel

Light (upper bar) triggers a current through the Chop 1 photoreceptor. Nagel/AAAS

Anewly discovered rhodopsin does double duty as light detector and proton channel, say Georg Nagel (Max-Planck-Institut für Biophysik, Frankfurt am Main, Germany), Peter Hegemann (Universität Regensburg, Germany), and colleagues. Meanwhile, a group led by John Spudich at the University of Texas (Houston, TX) has used RNA interference to show that this and another channel are the two rhodopsins that the alga Chlamydomonas reinhardtii uses to determine whether to move closer to or further from a light source.

Previously, Hegemann has purified algal proteins that bind retinal, the light-detecting chromophore, but they turned out not to be the detector for phototaxis. His latest candidate, which was named channelrhodopsin-1 (Chop 1), came from a database search. The sequence is similar to that of bacteriorhodopsin, which passes protons from one residue to another thus acting as a pump. Although this network of residues is intact in Chop 1, some of these Chop 1 residues can be mutated without destroying proton conductance. Furthermore, Chop 1 produced in frog oocytes cannot move protons against a gradient, as with the pump bacteriorhodopsin, but acts like a channel that allows diffusion in either direction.The researchers are not surprised by the two-in-one protein, as the speed with which Chlamydomonas reacts to light had suggested a direct connection between light detection and ion conductance. Now, they want to understand how a pump like bacteriorhodopsin can be modified to make a channel that may be gated by retinal.

References:

Nagel, G., et al. 2002. Science. 296:2395–2398; Sineshchekov, O.A., et al. 2002. Proc. Natl. Acad. Sci. USA. 99:8689–8694.[Abstract/Free Full Text]

William A. Wells

wellsw{at}rockefeller.edu

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This Article Full Text (PDF, 302K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Wells, W. A. Search for Related Content PubMed Articles by Wells, W. A. Social Bookmarking                            What's this?