Abstract

The bacterial type VI secretion system (T6SS) uses contraction of a long sheath to quickly thrust a tube with associated effectors across membranes of eukaryotic and bacterial cells1,2,3,4,5. Only limited structural information is available about the inherently unstable precontraction state of the T6SS. Here, we obtain a 3.7 Å resolution structure of a non-contractile sheath–tube complex using cryo-electron microscopy and show that it resembles the extended T6SS inside Vibrio cholerae cells. We build a pseudo-atomic model of the complete sheath–tube assembly, which provides a mechanistic understanding of coupling sheath contraction with pushing and rotating the inner tube for efficient target membrane penetration. Our data further show that sheath contraction exposes a buried recognition domain to specifically trigger the disassembly and recycling of the T6SS sheath by the cognate ATP-dependent unfoldase ClpV.

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Acknowledgements

The work was supported by Swiss National Science Foundation (SNSF) grant 31003A_159525 and the University of Basel. H.S. acknowledges support from the SNSF NCCR TransCure. Calculations were performed at sciCORE (http://scicore.unibas.ch/) scientific computing core facility at the University of Basel. We acknowledge S. Ursich for the help in sample preparation for cryo-ET.

Author information

Affiliations

  1. Focal Area Infection Biology, Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056, Basel, Switzerland

    • Jing Wang
    • , Maximilian Brackmann
    •  & Marek Basler
  2. Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, Mattenstrasse 26, CH-4058, Basel, Switzerland

    • Daniel Castaño-Díez
    • , Kenneth N. Goldie
    •  & Henning Stahlberg
  3. BioEM Lab, Biozentrum, University of Basel, Mattenstrasse 26, CH-4058, Basel, Switzerland

    • Daniel Castaño-Díez
  4. Max Planck Institute of Biophysics, Max-von-Laue Str. 3, 60438, Frankfurt am Main, Germany

    • Mikhail Kudryashev
  5. Buchmann Institute for Molecular Life Sciences, Max-von-Laue Str. 17, 60438, Frankfurt am Main, Germany

    • Mikhail Kudryashev
  6. Focal Area Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056, Basel, Switzerland

    • Timm Maier
    •  & Henning Stahlberg

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Contributions

J.W. collected cryo-electron microscopy data, performed image processing and generated atomic models. M.Br. isolated and purified the sheaths. M.K. performed some initial electron microscopy data collection and data analysis. D.C.-D. provided support and contributed to data analysis. K.N.G. and H.S. provided support and supervised data collection. T.M. contributed to and advised on atomic model building. M.Ba. conceived the project and analysed the data. M.Br., J.W. and M.Ba. wrote the manuscript. All authors read the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Marek Basler.

Electronic supplementary material

  1. Life Sciences Reporting Summary

    Supplementary Figures 1–5, Supplementary Tables 1–6, Supplementary Video legends.

  2. Life sciences reporting summary.

  3. Supplementary Video 1

    Details of tomography reconstruction of the wild-type extended sheath, VipA-N3 sheath structure and Hcp tube.

  4. Supplementary Video 2

    Proposed mechanism of T6SS assembly and contraction.

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DOI

https://doi.org/10.1038/s41564-017-0020-7

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