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  Proteorhodopsin is a light-driven proton pump with variable vectoriality

Friedrich, T., Geibel, S., Kalmbach, R., Chizhov, I., Ataka, K., Heberle, J., et al. (2002). Proteorhodopsin is a light-driven proton pump with variable vectoriality. Journal of Molecular Biology, 321(5): 1, pp. 821-838. Retrieved from http://dx.doi.org/10.1016/S0022-2836(02)00696-4.

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Genre: Zeitschriftenartikel
Alternativer Titel : J. Mol. Biol.

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 Urheber:
Friedrich, Thomas1, Autor
Geibel, Sven1, Autor
Kalmbach, Rolf1, Autor
Chizhov, Igor1, Autor
Ataka, Kenichi, Autor
Heberle, Joachim, Autor
Engelhard, Martin2, Autor           
Bamberg, Ernst1, Autor
Affiliations:
1Max Planck Institute of Molecular Physiology, Max Planck Society, ou_1753286              
2Abt. III: Physikalische Biochemie, Max Planck Institute of Molecular Physiology, Max Planck Society, ou_1753289              

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Schlagwörter: Schiff base proton acceptor; photocurrents; photocycle; pH dependence; two-photon process
 Zusammenfassung: Proteorhodopsin, a homologue of archaeal bacteriorhodopsin (BR), belongs to a newly identified family of retinal proteins from marine bacteria, which could play an important role in the energy balance of the biosphere. We cloned the cDNA sequence of proteorhodopsin by chemical gene synthesis, expressed the protein in Escherichia coli cells, purified and reconstituted the protein in its functional active state. The photocycle characteristics were determined by time-resolved absorption and Fourier transform infrared (FT-IR) spectroscopy. The pH- dependence of the absorption spectrum indicates that the pK(a) of the primary acceptor of the Schiff base proton (Asp97) is 7.68. Generally, the photocycle of proteorhodopsin is similar to that of BR, although an L-like photocycle intermediate was not detectable. Whereas at pH > 7 an M-like intermediate is formed upon illumination, at pH 5 no M-like intermediate could be detected. As the photocycle kinetics do not change between the acidic and alkaline state of proteorhodopsin, the only difference between these two forms is the protonation status of Asp97. This is corroborated by time-resolved FT-IR spectroscopy, which demonstrates that proton transfer from the retinal Schiff base to Asp97 is observed at alkaline pH, but the other vibrational changes are essentially pH-independent. After reconstitution into proteoliposomes, light-induced proton currents of proteorhodopsin were measured in a compound membrane system where proteoliposomes were adsorbed to planar lipid bilayers. Our results show that proteorhodopsin is a light-driven proton pump with characteristics similar to those of BR at alkaline pH. However, at acidic pH, the direction of proton pumping is inverted. Complementary experiments were carried out on proteorhodopsin expressed heterologously in Xenopus laevis oocytes under voltage clamp conditions. The following results were obtained. (1) At alkaline pH, proteorhodopsin mediates outwardly directed proton pumping like BR. (2) The direction of proton pumping can be inverted, when Asp97 is protonated. (3) The current can be inverted by changes of the polarity of the applied voltage. (4) The light intensity-dependence of the photocurrents leads to the conclusion that the alkaline form of proteorhodopsin shows efficient proton pumping after sequential excitation by two photons. (C) 2002 Elsevier Science Ltd. All rights reserved.

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Sprache(n): eng - English
 Datum: 2002-08-30
 Publikationsstatus: Erschienen
 Seiten: -
 Ort, Verlag, Ausgabe: -
 Inhaltsverzeichnis: -
 Art der Begutachtung: Expertenbegutachtung
 Identifikatoren: eDoc: 15089
URI: http://dx.doi.org/10.1016/S0022-2836(02)00696-4
 Art des Abschluß: -

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Titel: Journal of Molecular Biology
  Alternativer Titel : J. Mol. Biol.
Genre der Quelle: Zeitschrift
 Urheber:
Affiliations:
Ort, Verlag, Ausgabe: -
Seiten: - Band / Heft: 321 (5) Artikelnummer: 1 Start- / Endseite: 821 - 838 Identifikator: -