Assembly and channel opening of outer membrane protein in tripartite drug efflux pumps of Gram-negative bacteria

J Biol Chem. 2012 Apr 6;287(15):11740-50. doi: 10.1074/jbc.M111.329375. Epub 2012 Feb 3.


Gram-negative bacteria are capable of expelling diverse xenobiotic substances from within the cell by use of three-component efflux pumps in which the energy-activated inner membrane transporter is connected to the outer membrane channel protein via the membrane fusion protein. In this work, we describe the crystal structure of the membrane fusion protein MexA from the Pseudomonas aeruginosa MexAB-OprM pump in the hexameric ring arrangement. Electron microscopy study on the chimeric complex of MexA and the outer membrane protein OprM reveals that MexA makes a tip-to-tip interaction with OprM, which suggests a docking model for MexA and OprM. This docking model agrees well with genetic results and depicts detailed interactions. Opening of the OprM channel is accompanied by the simultaneous exposure of a protein structure resembling a six-bladed cogwheel, which intermeshes with the complementary cogwheel structure in the MexA hexamer. Taken together, we suggest an assembly and channel opening model for the MexAB-OprM pump. This study provides a better understanding of multidrug resistance in Gram-negative bacteria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Bacterial Outer Membrane Proteins / chemistry*
  • Bacterial Outer Membrane Proteins / ultrastructure
  • Binding Sites
  • Crystallography, X-Ray
  • Drug Resistance, Multiple, Bacterial*
  • Membrane Transport Proteins / chemistry*
  • Membrane Transport Proteins / ultrastructure
  • Microscopy, Electron
  • Models, Molecular
  • Molecular Sequence Data
  • Peptidoglycan / chemistry
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Multimerization*
  • Protein Structure, Quaternary
  • Pseudomonas aeruginosa*
  • Surface Properties


  • Bacterial Outer Membrane Proteins
  • Membrane Transport Proteins
  • MexA protein, Pseudomonas aeruginosa
  • OprM protein, Pseudomonas aeruginosa
  • Peptidoglycan

Associated data

  • PDB/4DK0
  • PDB/4DK1