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Biophys J, November 2001, p. 2897-2907, Vol. 81, No. 5

Photoreceptor Current and Photoorientation in Chlamydomonas Mediated by 9-Demethylchlamyrhodopsin

Elena G. Govorunova,*dagger Oleg A. Sineshchekov,* Wolfgang Gärtner,Dagger Alexander S. Chunaev,§ and Peter Hegemanndagger

 *Biology Faculty, Moscow State University, 119899 Moscow, Russia;  dagger Institute for Biochemistry I, Regensburg University, D-93040 Regensburg, Germany;  Dagger Max-Planck-Institut für Strahlenchemie, D-45413 Mülheim an der Ruhr, Germany; and  §Biology Faculty, St. Petersburg State University, 199164 St. Petersburg, Russia

Green flagellates possess rhodopsin-like photoreceptors involved in control of their behavior via generation of photocurrents across the plasma membrane. Chlamydomonas mutants blocked in retinal biosynthesis are "blind," but they can be rescued by the addition of exogenous retinoids. Photosignaling by chlamyrhodopsin regenerated with 9-demethylretinal was investigated by recording photocurrents from single cells and cell suspensions, and by measuring phototactic orientation. The addition of a saturating concentration of this analog led to reconstitution of all receptor molecules. However, sensitivity of the photoreceptor current in cells reconstituted with the analog was smaller compared with retinal-reconstituted cells, indicating a decreased signaling efficiency of the analog receptor protein. Suppression of the photoreceptor current in double-flash experiments was smaller and its recovery faster with 9-demethylretinal than with retinal, as it would be expected from a decreased PC amplitude in the analog-reconstituted cells. Cells reconstituted with either retinal or the analog displayed negative phototaxis at low light and switched to positive one upon an increase in stimulus intensity, as opposed to the wild type. The reversal of the phototaxis direction in analog-reconstituted cells was shifted to a higher fluence rate compared with cells reconstituted with retinal, which corresponded to the decreased signaling efficiency of 9-demethylchlamyrhodopsin.

Biophys J, November 2001, p. 2897-2907, Vol. 81, No. 5
© 2001 by the Biophysical Society   0006-3495/01/11/2897/11  $2.00




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Copyright © 2001 by the Biophysical Society.