Letter | Published:

Structure of the AcrAB–TolC multidrug efflux pump

Nature volume 509, pages 512515 (22 May 2014) | Download Citation


The capacity of numerous bacterial species to tolerate antibiotics and other toxic compounds arises in part from the activity of energy-dependent transporters. In Gram-negative bacteria, many of these transporters form multicomponent ‘pumps’ that span both inner and outer membranes and are driven energetically by a primary or secondary transporter component1,2,3,4,5,6,7. A model system for such a pump is the acridine resistance complex of Escherichia coli1. This pump assembly comprises the outer-membrane channel TolC, the secondary transporter AcrB located in the inner membrane, and the periplasmic AcrA, which bridges these two integral membrane proteins. The AcrAB–TolC efflux pump is able to transport vectorially a diverse array of compounds with little chemical similarity, thus conferring resistance to a broad spectrum of antibiotics. Homologous complexes are found in many Gram-negative species, including in animal and plant pathogens. Crystal structures are available for the individual components of the pump2,3,4,5,6,7 and have provided insights into substrate recognition, energy coupling and the transduction of conformational changes associated with the transport process. However, how the subunits are organized in the pump, their stoichiometry and the details of their interactions are not known. Here we present the pseudo-atomic structure of a complete multidrug efflux pump in complex with a modulatory protein partner8 from E. coli. The model defines the quaternary organization of the pump, identifies key domain interactions, and suggests a cooperative process for channel assembly and opening. These findings illuminate the basis for drug resistance in numerous pathogenic bacterial species.

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Primary accessions

Data deposits

Atomic coordinates and structure factors for the reported crystal structures have been deposited in the PDB under accessions 4C48 (AcrB/AcrZ/DARPin) and 4CDI (AcrB/AcrZ). The cryo-EM map has been deposited in the Electron Microscopy Data Bank under accession EMD-5915.


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This work was supported by the Wellcome Trust and Human Frontier Science Program (B.L.) and partly by a National Institutes of Health grant (P41GM103832 to W.C.). J.E.V. is supported by a Herschel Smith scholarship. T.O.-A. is the recipient of a Cambridge Trust scholarship, an Adam Glinsman award and a Faculty for the Future Fellowship from the Schlumberger Foundation. We thank M. Pos for kindly providing pBAD-AcrAB-TolC. We thank L. Packman for mass-spectrometric analyses and S. J. Ludtke, M. F. Schmid, M. Pos and R. van Veen for helpful advice and discussions. We are grateful to the staff at the Diamond Light Source for access to facilities and invaluable help.

Author information


  1. Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK

    • Dijun Du
    • , Nathan R. James
    • , Jarrod E. Voss
    • , Ewa Klimont
    •  & Ben F. Luisi
  2. National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA

    • Zhao Wang
    •  & Wah Chiu
  3. Department of Pharmacology, Tennis Court Road, Cambridge CB2 1PD, UK

    • Thelma Ohene-Agyei
  4. School of Pharmacy & Medical Sciences, Sansom Institute for Health Research, University of South Australia, Adelaide, South Australia 5000, Australia

    • Henrietta Venter


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D.D., W.C. and B.F.L. designed the experiments; D.D. and N.R.J. purified and crystallized AcrBZ complexes. D.D. and B.F.L. solved the crystal structure of AcrBZ complexes. D.D., N.R.J. and E.K. purified AcrABZ–TolC complexes. Z.W., J.E.V. and W.C. obtained and analysed the single-particle cryo-EM data. D.D. and B.F.L. devised a model of AcrABZ–TolC based on the cryo-EM map. T.O.-A. and H.V. conducted MIC and efflux assays on the AcrABZ–TolC pump. D.D., J.E.V., W.C. and B.F.L. analysed results. All authors contributed to writing the manuscript.

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The authors declare no competing financial interests.

Corresponding authors

Correspondence to Dijun Du or Ben F. Luisi.

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