Lipid-layer crystallization and preliminary three-dimensional structural analysis of AcrA, the periplasmic component of a bacterial multidrug efflux pump

J Struct Biol. 2001 Oct;136(1):81-8. doi: 10.1006/jsbi.2001.4418.


The multidrug efflux complex AcrAB-TolC confers intrinsic drug resistance in Escherichia coli by pumping antibiotics out of the cell. We determined a low-resolution (20 A) structure of AcrA, the periplasmic component, by electron crystallography. Expressed with a His-tag at its carboxyl-terminus, the protein bound to lipid layers containing the nickel-chelating phospholipid DOGS-NTA. Under the lipid layers, AcrA crystallized in layer group P2(1)22, with a unit cell size of 157 by 95 A and a thickness of about 100 A. The four asymmetric units in the unit cell are organized into what appears to be two rings, each with a central opening of 30 A in diameter. Within each ring, the density can be interpreted as following a pseudo-helical path, approximately 210 A long. This length matches that of monomeric AcrA in solution, previously estimated by light scattering and hydrodynamic measurements. On one side the density has a tubular shape, with a thickness of about 25 A, while on the other side the densities of the upper and lower parts of the pseudo-helical path are fused into a shield.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / chemistry*
  • Carrier Proteins*
  • Crystallography / methods
  • Escherichia coli / metabolism
  • Escherichia coli Proteins*
  • Fourier Analysis
  • Lipoproteins / chemistry*
  • Membrane Proteins / chemistry
  • Membrane Transport Proteins
  • Microscopy, Electron / methods
  • Models, Molecular
  • Multidrug Resistance-Associated Proteins
  • Periplasm / chemistry


  • AcrA protein, E coli
  • AcrB protein, E coli
  • Bacterial Proteins
  • Carrier Proteins
  • Escherichia coli Proteins
  • Lipoproteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • Multidrug Resistance-Associated Proteins