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Helix deformation is coupled to vectorial proton transport in the photocycle of bacteriorhodopsin

Nature volume 406, pages 645–648 (2000)Cite this article

Abstract

A wide variety of mechanisms are used to generate a proton-motive potential across cell membranes, a function lying at the heart of bioenergetics. Bacteriorhodopsin, the simplest known proton pump1, provides a paradigm for understanding this process. Here we report, at 2.1 Å resolution, the structural changes in bacteriorhodopsin immediately preceding the primary proton transfer event in its photocycle. The early structural rearrangements2 propagate from the protein's core towards the extracellular surface, disrupting the network of hydrogen-bonded water molecules that stabilizes helix C in the ground state. Concomitantly, a bend of this helix enables the negatively charged3 primary proton acceptor, Asp 85, to approach closer to the positively charged primary proton donor, the Schiff base. The primary proton transfer event would then neutralize these two groups, cancelling their electrostatic attraction and facilitating a relaxation of helix C to a less strained geometry. Reprotonation of the Schiff base by Asp 85 would thereby be impeded, ensuring vectorial proton transport. Structural rearrangements also occur near the protein's surface, aiding proton release to the extracellular medium.

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Figure 1: Spectral characterization of a bacteriorhodopsin (bR) intermediate trapped within a single crystal.
Figure 2: Structural changes in bacteriorhodopsin resulting from photoexcitation at 170 K.
Figure 3: Detailed view of electron density changes overlaid on the ground state model and contoured to 3.4 σ.
Figure 4: Structural rearrangements facilitating the primary proton transfer event.
Figure 5: The r.m.s. deviation between the backbones of the refined LLT model (Table 1) and the ground state bacteriorhodopsin versus the residue number.

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Acknowledgements

We thank H. Belrhali, D. Bourgeois, J. Hajdu, A. Hardmeyer, J. Navarro, P. Nollert, H. Pettersson and S. Ramaswamy for experimental contributions and discussions, and G. Büldt for providing purple membrane. Support from the EU-BIOTECH, the Swedish Natural Science Research Council (NFR) and the Swiss National Science Foundation's SPP BIOTECH is gratefully acknowledged.

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Author notes

  1. Ehud M. Landau

    Present address: Department of Physiology and Biophysics and Sealy Center for Structural Biology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas, 77555-0641, USA

  2. Antoine Royant, Karl Edman and Ehud M. Landau: These authors contributed equally to this work.

Authors and Affiliations

  1. Institut de Biologie Structurale, CEA-CNRS-Université Joseph Fourier, UMR 5075, 41 rue Jules Horowitz, Grenoble, Cedex 1, F-38027, France

    Antoine Royant, Thomas Ursby & Eva Pebay-Peyroula

  2. European Synchrotron Radiation Facility , 6 rue Jules Horowitz, BP 220, Grenoble Cedex, F-38043, France

    Antoine Royant & Thomas Ursby

  3. Department of Biochemistry, Uppsala University, Biomedical Centre, Box 576, Uppsala , S-751 23, Sweden

    Karl Edman & Richard Neutze

  4. Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, 4056, Switzerland

    Ehud M. Landau

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Correspondence to Ehud M. Landau.

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Royant, A., Edman, K., Ursby, T. et al. Helix deformation is coupled to vectorial proton transport in the photocycle of bacteriorhodopsin. Nature 406, 645–648 (2000). https://doi.org/10.1038/35020599

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