Intrinsic conformational plasticity of native EmrE provides a pathway for multidrug resistance

J Am Chem Soc. 2014 Jun 4;136(22):8072-80. doi: 10.1021/ja503145x. Epub 2014 May 23.


EmrE is a multidrug resistance efflux pump with specificity to a wide range of antibiotics and antiseptics. To obtain atomic-scale insight into the attributes of the native state that encodes the broad specificity, we used a hybrid of solution and solid-state NMR methods in lipid bilayers and bicelles. Our results indicate that the native EmrE dimer oscillates between inward and outward facing structural conformations at an exchange rate (k(ex)) of ~300 s(-1) at 37 °C (millisecond motions), which is ~50-fold faster relative to the tetraphenylphosphonium (TPP(+)) substrate-bound form of the protein. These observables provide quantitative evidence that the rate-limiting step in the TPP(+) transport cycle is not the outward-inward conformational change in the absence of drug. In addition, using differential scanning calorimetry, we found that the width of the gel-to-liquid crystalline phase transition was 2 °C broader in the absence of the TPP(+) substrate versus its presence, which suggested that changes in transporter dynamics can impact the phase properties of the membrane. Interestingly, experiments with cross-linked EmrE showed that the millisecond inward-open to outward-open dynamics was not the culprit of the broadening. Instead, the calorimetry and NMR data supported the conclusion that faster time scale structural dynamics (nanosecond-microsecond) were the source and therefore impart the conformationally plastic character of native EmrE capable of binding structurally diverse substrates. These findings provide a clear example how differences in membrane protein transporter structural dynamics between drug-free and bound states can have a direct impact on the physical properties of the lipid bilayer in an allosteric fashion.

Publication types

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

MeSH terms

  • Antiporters / chemistry*
  • Antiporters / genetics*
  • Cross-Linking Reagents
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Escherichia coli / chemistry
  • Escherichia coli / genetics
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics*
  • Indicators and Reagents
  • Lipid Bilayers
  • Magnetic Resonance Spectroscopy
  • Onium Compounds / chemistry
  • Organophosphorus Compounds / chemistry
  • Protein Conformation


  • Antiporters
  • Cross-Linking Reagents
  • Escherichia coli Proteins
  • Indicators and Reagents
  • Lipid Bilayers
  • Onium Compounds
  • Organophosphorus Compounds
  • EmrE protein, E coli
  • tetraphenylphosphonium