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Nature 419, 484-487 (3 October 2002) | doi:10.1038/nature01109; Received 9 May 2002; Accepted 16 July 2002

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Molecular basis of transmembrane signalling by sensory rhodopsin II–transducer complex

Valentin I. Gordeliy1,2, Jörg Labahn1, Rouslan Moukhametzianov1,2, Rouslan Efremov1,2, Joachim Granzin1, Ramona Schlesinger1, Georg Büldt1, Tudor Savopol4,5, Axel J. Scheidig4, Johann P. Klare4 & Martin Engelhard4

  1. Research Centre Jülich, Institute of Structural Biology (IBI-2), 52425 Jülich, Germany
  2. Centre for Biophysics and Physical Chemistry of Supramolecular Structures, MIPT, 141700, Moscow District, Russia
  3. Max-Planck-Institut für Molekulare Physiologie, Otto Hahn Str. 11, 44227 Dortmund, Germany
  4. Present address: Carol Davila Medical and Pharmaceutical University, POB15-205 Bucharest, Romania.

Correspondence to: Georg Büldt1Martin Engelhard4 Correspondence and requests for materials should be addressed to G.B. (e-mail: Email: g.bueldt@fz-juelich.de) or M.E. (e-mail: Email: martin.engelhard@mpi-dortmund.mpg.de). Coordinates have been deposited with the Research Collaboratory for Structural Bioinformatics Protein Data Bank under accession code 1H2S.

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Microbial rhodopsins, which constitute a family of seven-helix membrane proteins with retinal as a prosthetic group, are distributed throughout the Bacteria, Archaea and Eukaryota1, 2, 3. This family of photoactive proteins uses a common structural design for two distinct functions: light-driven ion transport and phototaxis. The sensors activate a signal transduction chain similar to that of the two-component system of eubacterial chemotaxis4. The link between the photoreceptor and the following cytoplasmic signal cascade is formed by a transducer molecule that binds tightly and specifically5 to its cognate receptor by means of two transmembrane helices (TM1 and TM2). It is thought that light excitation of sensory rhodopsin II from Natronobacterium pharaonis (SRII) in complex with its transducer (HtrII) induces an outward movement of its helix F (ref. 6), which in turn triggers a rotation of TM2 (ref. 7). It is unclear how this TM2 transition is converted into a cellular signal. Here we present the X-ray structure of the complex between N. pharaonis SRII and the receptor-binding domain of HtrII at 1.94 Å resolution, which provides an atomic picture of the first signal transduction step. Our results provide evidence for a common mechanism for this process in phototaxis and chemotaxis.