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Structure of the outer membrane complex of a type IV secretion system

Nature volume 462, pages 1011–1015 (2009)Cite this article

Abstract

Type IV secretion systems are secretion nanomachines spanning the two membranes of Gram-negative bacteria. Three proteins, VirB7, VirB9 and VirB10, assemble into a 1.05 megadalton (MDa) core spanning the inner and outer membranes. This core consists of 14 copies of each of the proteins and forms two layers, the I and O layers, inserting in the inner and outer membrane, respectively. Here we present the crystal structure of a ∼0.6 MDa outer-membrane complex containing the entire O layer. This structure is the largest determined for an outer-membrane channel and is unprecedented in being composed of three proteins. Unexpectedly, this structure identifies VirB10 as the outer-membrane channel with a unique hydrophobic double-helical transmembrane region. This structure establishes VirB10 as the only known protein crossing both membranes of Gram-negative bacteria. Comparison of the cryo-electron microscopy (cryo-EM) and crystallographic structures points to conformational changes regulating channel opening and closing.

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Figure 1: The T4S system outer-membrane complex.
Figure 2: Ribbon diagram of the heterotrimer unit.
Figure 3: Inter-heterotrimeric interactions.
Figure 4: Transmembrane region of the T4S system outer-membrane complex and proposed mechanism of pore opening and closure.

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Primary accessions

Protein Data Bank

Data deposits

Structure factors and coordinates are deposited in the Protein Data Bank under accession number 3JQO.

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Acknowledgements

This work was funded by Wellcome Trust grant 082227 to G.W. We thank A. Thompson and the staff of beamline PROXIMA 1 at Soleil, the staff of beamline ID14.4 at the European Synchrotron Radiation Facility, and H. Saibil, E. Orlova and P. Christie for comments on the manuscript. We thank A. Kumar for help in implementing the immunofluorescence experiments.

Author Contributions V.C. produced the complex, optimized crystals, and built, refined and analysed the structure. R.F. designed the purification protocol, produced the complex, grew the first crystals, optimized crystals and analysed the structure. S.D. and J.N. solved the structure by molecular replacement and provided the electron density map. N.C. collected crystallographic data. G.W. supervised the work, analysed the structure and wrote the paper.

Author information

Author notes

  1. Vidya Chandran and Rémi Fronzes: These authors contributed equally to this work.

Authors and Affiliations

  1. Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, UK ,

    Vidya Chandran, Rémi Fronzes, Nora Cronin & Gabriel Waksman

  2. Virology Department and CNRS URA 3015, Institut Pasteur, Unité de Virologie Structurale, Paris, 25–28 Rue du Dr Roux, F-75724 Paris, France,

    Stéphane Duquerroy

  3. Université Paris-Sud, F-91405 Orsay, France

    Stéphane Duquerroy

  4. Laboratoire de Microscopie Electronique, Institut de Biologie Structurale J.P. Ebel, 41 rue Jules Horowitz, F-38027 Grenoble Cedex 1, France ,

    Jorge Navaza

Authors
  1. Vidya Chandran
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Corresponding author

Correspondence to Gabriel Waksman.

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This file contains a Supplementary Discussion, Supplementary Table 1, Supplementary Figures 1-10 with Legends and Supplementary References. (PDF 13100 kb)

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Chandran, V., Fronzes, R., Duquerroy, S. et al. Structure of the outer membrane complex of a type IV secretion system . Nature 462, 1011–1015 (2009). https://doi.org/10.1038/nature08588

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