Channelrhodopsin, insight into the light switch

Peter Hegemann, Andre Berndt, Matthias Prigge and Katja Stehfest

Experimental Biophysics, Humboldt Universität zu Berlin, Berlin, Germany

Channelrhodpsins ChR1 and ChR2 are the sensory photoreceptors for phototaxis and photbic responses in Chlamydomonas and Volvox. They are 7TM membrane proteins with retinal as the light sensing chromophore and they are functioning as light-gated ion channels. Based on the 3D model derived from the X-ray structure of related microbial rhodopsin we have modified the chromophore binding site under alteration of the absorption spectrum, the ion selectivity, and the life time of the conducting state. The ion channel properties were studied in Xenopus oocytes and HEK cells and finally in cooperation with Deisseroth group (Stanford) in hippocampal neurons. Selected recombinant ChRs were expressed in green monkey COS cells and P.pastoris, and the purified proteins were studied using time resolved spectroscopy. We will present a photocycle model with several side reaction that will demonstrate the complexity of these unique sensory photoreceptors. (1) Ritter, E., Stehfest, K., Berndt, A., Hegemann, P., Bartl, F. (2008) Monitoring light-induced structural changes of Channelrhodopsin-2 by UV/Vis and FTIR spectroscopy. J. Biol. Chem. 283, 35033-41. (2) Berndt, A., Yizhar, O., Gunaydin, L., Hegemann, P., and Deisseroth, K. (2009) Bistable neural state switches. Nature Neurosci. 12, 229-34. (3) Kianianmomeni, A., Stehfest, K., Nematollahi, G., Hegemann, P., and Hallmann, A. (2009) Channelrhodopsins of Volvox carteri are Photochromic Proteins Specifically Expressed in Somatic Cells under Control of Light, Temperature and the Sex-Inducer. Plant Phys.151:347-66. (4) Guanaydin, L., Yizhar, O., Berndt, A., Sohal, V., Deisseroth, K., and Hegemann, P. (2010) Ultrafast optogenetics: precise neural control beyond the gamma band. Nature Neurosci. 13, 387-393.

e-mail address of presenting author: Hegemann@rz.hu-berlin.de

web site: http://www2.hu-berlin.de/biologie/expbp/