In situ structure and assembly of the multidrug efflux pump AcrAB-TolC

Nat Commun. 2019 Jun 14;10(1):2635. doi: 10.1038/s41467-019-10512-6.


Multidrug efflux pumps actively expel a wide range of toxic substrates from the cell and play a major role in intrinsic and acquired drug resistance. In Gram-negative bacteria, these pumps form tripartite assemblies that span the cell envelope. However, the in situ structure and assembly mechanism of multidrug efflux pumps remain unknown. Here we report the in situ structure of the Escherichia coli AcrAB-TolC multidrug efflux pump obtained by electron cryo-tomography and subtomogram averaging. The fully assembled efflux pump is observed in a closed state under conditions of antibiotic challenge and in an open state in the presence of AcrB inhibitor. We also observe intermediate AcrAB complexes without TolC and discover that AcrA contacts the peptidoglycan layer of the periplasm. Our data point to a sequential assembly process in living bacteria, beginning with formation of the AcrAB subcomplex and suggest domains to target with efflux pump inhibitors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology
  • Bacterial Outer Membrane Proteins / metabolism*
  • Carrier Proteins / drug effects
  • Carrier Proteins / physiology*
  • Carrier Proteins / ultrastructure
  • Cryoelectron Microscopy / methods
  • Drug Resistance, Multiple, Bacterial / drug effects
  • Electron Microscope Tomography / methods
  • Escherichia coli / drug effects
  • Escherichia coli / physiology*
  • Escherichia coli / ultrastructure
  • Escherichia coli Proteins / antagonists & inhibitors
  • Escherichia coli Proteins / drug effects
  • Escherichia coli Proteins / metabolism*
  • Escherichia coli Proteins / physiology*
  • Escherichia coli Proteins / ultrastructure
  • Intravital Microscopy / methods
  • Lipoproteins / metabolism*
  • Membrane Transport Proteins / metabolism*
  • Multidrug Resistance-Associated Proteins / antagonists & inhibitors
  • Multidrug Resistance-Associated Proteins / metabolism*
  • Peptidoglycan / metabolism
  • Periplasm / metabolism
  • Protein Binding / drug effects
  • Protein Structure, Quaternary / drug effects


  • AcrA protein, E coli
  • AcrAB-TolC protein, E coli
  • AcrB protein, E coli
  • Anti-Bacterial Agents
  • Bacterial Outer Membrane Proteins
  • Carrier Proteins
  • Escherichia coli Proteins
  • Lipoproteins
  • Membrane Transport Proteins
  • Multidrug Resistance-Associated Proteins
  • Peptidoglycan
  • tolC protein, E coli