Characterization of the multidrug efflux regulator AcrR from Escherichia coli

Biochem Biophys Res Commun. 2007 Sep 14;361(1):85-90. doi: 10.1016/j.bbrc.2007.06.175. Epub 2007 Jul 17.


The Escherichia coli AcrR represses transcription of the acrB gene, which encodes the multidrug efflux pump AcrB that extrudes a wide variety of toxic compounds, by binding its target operator DNA. Fluorescence polarization was performed using purified, recombinant AcrR that contains a 6xHis tag at the C-terminus and a fluorescein-labeled 28-base pair oligonucleotide bearing a predicted palindrome (IR) operator sequence. Binding of AcrR to the predicted IR sequence occurred with a dissociation constant (K(D)) in the nanomolar range. Fluorescence polarization assays were also applied to characterize the affinity and specificity of AcrR interaction with three different fluorescent ligands, rhodamine 6G, ethidium, and proflavin. The K(D) values for these ligands range from 4.2 to 10.1 microM, suggesting that AcrR is capable of recognizing a wide range of structurally dissimilar toxic compounds as it is in the case of the AcrB multidrug efflux pump. We found that the binding of rhodamine 6G to AcrR is inhibited by the presence of ethidium. In contrast, the dissociation constant of proflavin binding to AcrR was not affected by ethidium, a result suggesting that ethidium and proflavin are bound to distinct binding sites.

Publication types

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

MeSH terms

  • Binding Sites
  • DNA, Bacterial / chemistry
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Ethidium / metabolism
  • Ligands
  • Multidrug Resistance-Associated Proteins / genetics
  • Operator Regions, Genetic*
  • Proflavine / metabolism
  • Repressor Proteins / metabolism*


  • AcrR protein, E coli
  • DNA, Bacterial
  • Escherichia coli Proteins
  • Ligands
  • Multidrug Resistance-Associated Proteins
  • Repressor Proteins
  • Proflavine
  • Ethidium