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Biophys. J. BioFAST: First Published April 7, 2006. doi:10.1529/biophysj.105.074690
© 2006 by the Biophysical Society.

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PHOTOBIOPHYSICS

First Steps of Retinal Photoisomerization in Proteorhodopsin

Martin O Lenz 1, Robert Huber 2, Bernhard Schmidt 3, Peter Gilch 3, Rolf Kalmbach 4, Martin Engelhard 4 and Josef Wachtveitl 5*

1 University Frankfurt/ Main, Germany
2 University of Frankfurt/ Main, Germany
3 Universität München
4 Max-Planck-Institute of Molecular Physiology
5 Goethe Universität Frankfurt am Main

* To whom correspondence should be addressed. E-mail: wveitl{at}theochem.uni-frankfurt.de.

Submitted on September 19, 2005
Revised on November 7, 2005
Accepted on 22 March 2006


  Abstract
The early steps (< 1 ns) in the photocycle of the detergent solubilized proton pump proteorhodopsin (PR) are analyzed by ultrafast spectroscopic techniques. A comparison to the first primary events in reconstituted PR (Huber et. al., Biochemistry, 44:1800-1806) as well as to the well known archaeal proton pump bacteriorhodopsin (BR) is given. A dynamic Stokes shift observed in fs-time resolved fluorescence experiments allows a direct observation of early motions on the excited state potential energy surface. The initial dynamics is dominated by sequentially emerging stretching (<150 fs) and torsional (~300 fs) modes of the retinal. The different protonation states of the primary proton acceptor Asp97 drastically affect the reaction rate and the overall quantum efficiencies of the isomerization reactions, mainly evidenced for time scales above 1 ps. However, no major influence on the fast time scales (~150 fs) could be seen, indicating that the movement out of the Franck-Condon region is fairly robust to electrostatic changes in the retinal binding pocket. Based on fs-time-resolved absorption and fluorescence spectra, ground and exited state contributions can be disentangled and allow to construct a reaction model that consistently explains pH-dependent effects in solubilized and reconstituted PR.

Key Words: Bacteriorhodopsin, Femtosecond spectroscopy, Photochemical reaction cycle, Reaction dynamics, Retinal, Schiff base




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K. Neumann, M.-K. Verhoefen, I. Weber, C. Glaubitz, and J. Wachtveitl
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A. Rupenyan, I. H. M. van Stokkum, J. C. Arents, R. van Grondelle, K. Hellingwerf, and M. L. Groot
Characterization of the Primary Photochemistry of Proteorhodopsin with Femtosecond Spectroscopy
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Copyright © 2006 by the Biophysical Society.