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High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle

Nature volume 401, pages 822–826 (1999)Cite this article

Abstract

Bacteriorhodopsin is the simplest known photon-driven proton pump1 and as such provides a model for the study of a basic function in bioenergetics. Its seven transmembrane helices2 encompass a proton translocation pathway containing the chromophore, a retinal molecule covalently bound to lysine 216 through a protonated Schiff base, and a series of proton donors and acceptors. Photoisomerization of the all-trans retinal to the 13-cis configuration initiates the vectorial translocation of a proton from the Schiff base, the primary proton donor, to the extracellular side, followed by reprotonation of the Schiff base from the cytoplasm. Here we describe the high-resolution X-ray structure of an early intermediate in the photocycle of bacteriorhodopsin, which is formed directly after photoexcitation. A key water molecule is dislocated, allowing the primary proton acceptor, Asp 85, to move. Movement of the main-chain Lys 216 locally disrupts the hydrogen-bonding network of helix G, facilitating structural changes later in the photocycle.

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Figure 1: Key events in the photocycle of bacteriorhodopsin (bR).
Figure 2: Spectral characterization of a single crystal of bacteriorhodopsin.
Figure 3: Structural changes in bacteriorhodopsin resulting from photoexcitation at 110 K.
Figure 4: Detailed view of the observed electron-density differences (yellow, negative; blue, positive) overlaid on the ground-state structure, contoured to 3.5σ.
Figure 5: Stereo view of the structure of the early intermediate in the bacteriorhodopsin photocycle.

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Acknowledgements

We thank D. Bourgeois, L.-O. Essen, R. Henderson, D. Oesterhelt, J. P. Rosenbusch, I. Schlichting and S. Subramaniam for discussions; W. P. Burmeister, A. Hardmeyer, T. Taylor and R. Wouts for experimental contributions; and G. Büldt for providing purple membrane. Support from the EU-BIOTECH, the Swedish Research Council NFR, the Institut Universitaire de France and the Swiss National Science Foundation's SPP BIOTECH is acknowledged. K.E. was an undergraduate student in the Molecular Biotechnology Programme of Uppsala University.

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Author notes

  1. Peter Nollert

    Present address: Department of Biochemistry and Biophysics, UCSF, San Francisco, California, 94143-0448, USA

  2. Karl Edman, Peter Nollert and Antoine Royant: These authors contributed equally to this work

Authors and Affiliations

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

    Karl Edman, Janos Hajdu & Richard Neutze

  2. Department of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland

    Peter Nollert & Ehud M. Landau

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

    Antoine Royant & Eva Pebay-Peyroula

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

    Antoine Royant & Hassan Belrhali

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Correspondence to Eva Pebay-Peyroula, Richard Neutze or Ehud M. Landau.

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Edman, K., Nollert, P., Royant, A. et al. High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle. Nature 401, 822–826 (1999). https://doi.org/10.1038/44623

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