pH-dependent transitions in xanthorhodopsin.

Photochemistry and Photobiology
E S ImashevaJanos K Lanyi

Abstract

Xanthorhodopsin (XR), the light-driven proton pump of the halophilic eubacterium Salinibacter ruber, exhibits substantial homology to bacteriorhodopsin (BR) of archaea and proteorhodopsin (PR) of marine bacteria, but unlike them contains a light-harvesting carotenoid antenna, salinixanthin, as well as retinal. We report here the pH-dependent properties of XR. The pKa of the retinal Schiff base is as high as in BR, i.e. > or =12.4. Deprotonation of the Schiff base and the ensuing alkaline denaturation cause large changes in the absorption bands of the carotenoid antenna, which lose intensity and become broader, making the spectrum similar to that of salinixanthin not bound to XR. A small redshift of the retinal chromophore band and increase of its extinction, as well as the pH-dependent amplitude of the M intermediate indicate that in detergent-solubilized XR the pKa of the Schiff base counterion and proton acceptor is about 6 (compared to 2.6 in BR, and 7.5 in PR). The protonation of the counterion is accompanied by a small blueshift of the carotenoid absorption bands. The pigment is stable in the dark upon acidification to pH 2. At pH < 2 a transition to a blueshifted species absorbing around 440 nm occurs, accompanied by loss...Continue Reading

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Citations

Nov 26, 2010·The Journal of Membrane Biology·Eleonora S ImashevaJanos K Lanyi
Oct 17, 2008·Proceedings of the National Academy of Sciences of the United States of America·Hartmut LueckeJanos K Lanyi
Apr 11, 2008·Photochemistry and Photobiology·Eleonora S ImashevaJanos K Lanyi
Oct 26, 2016·Biochimica Et Biophysica Acta·Shintaro NakamuraMakoto Demura
Jun 12, 2013·Biochimica Et Biophysica Acta·Leonid S Brown
Apr 6, 2017·The Journal of Physical Chemistry. B·Elena Smolensky KoganovMordechai Sheves
Aug 4, 2019·Scientific Reports·Takefumi MorizumiOliver P Ernst

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