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Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export

Nature volume 405, pages 914–919 (2000)Cite this article

Abstract

Diverse molecules, from small antibacterial drugs to large protein toxins, are exported directly across both cell membranes of Gram-negative bacteria. This export is brought about by the reversible interaction of substrate-specific inner-membrane proteins with an outer-membrane protein of the TolC family, thus bypassing the intervening periplasm. Here we report the 2.1-Å crystal structure of TolC from Escherichia coli, revealing a distinctive and previously unknown fold. Three TolC protomers assemble to form a continuous, solvent-accessible conduit—a ‘channel-tunnel’ over 140 Å long that spans both the outer membrane and periplasmic space. The periplasmic or proximal end of the tunnel is sealed by sets of coiled helices. We suggest these could be untwisted by an allosteric mechanism, mediated by protein–protein interactions, to open the tunnel. The structure provides an explanation of how the cell cytosol is connected to the external environment during export, and suggests a general mechanism for the action of bacterial efflux pumps.

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Figure 1: The overall architecture of TolC.
Figure 2: Structural repeat in TolC.
Figure 3: Interfacial contacts in the α-helical barrel.
Figure 4: Surface representation of the TolC interior, illustrating the charge distribution.
Figure 5: Exterior view of the proximal end of the α-helical barrel, approximately down the threefold symmetry axis.

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Acknowledgements

We thank A. Thompson, K. Henderson, N. Duke, A. Joachimiak, Z. Otwinowski, W. Minor, K. Phillips, M. Symmons and F. von Delft for help during data collection and discussions; C. Calladine, M. Perutz, J. Li and C. Andersen for discussions; and G. Bricogne and P. Roversi for help with the BUSTER program. We acknowledge support for EU facility access for data collection at DESY (Hamburg) and ESRF (Grenoble). This work is supported by a Medical Research Council Programme grant (to V.K. and C.H.). A.S. and B.L. are supported by the Wellcome Trust.

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Author notes

  1. Vassilis Koronakis, Andrew Sharff and Ben Luisi: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK

    Vassilis Koronakis, Eva Koronakis & Colin Hughes

  2. Department of Biochemistry, Crystallography & Biocomputing Unit, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK

    Andrew Sharff & Ben Luisi

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  1. Vassilis Koronakis
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Correspondence to Vassilis Koronakis.

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Koronakis, V., Sharff, A., Koronakis, E. et al. Crystal structure of the bacterial membrane protein TolC central to multidrug efflux and protein export. Nature 405, 914–919 (2000). https://doi.org/10.1038/35016007

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