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EmrE dimerization depends on membrane environment.

Supratik Dutta1, Emma A Morrison1, Katherine A Henzler-Wildman1

  • 1Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660S. Euclid Ave., Box 8231, St. Louis, MO 63110, USA.

Biochimica Et Biophysica Acta
|April 1, 2014
PubMed
Summary
This summary is machine-generated.

The small multi-drug resistant (SMR) transporter EmrE forms a homodimer. Its stability varies significantly across different membrane environments, highlighting the crucial role of lipids in protein interactions.

Keywords:
Analytical ultra centrifugationEmrEFörster resonance energy transferMembrane mimeticOligomerizationTwo dimensional equilibrium constant (K(MD)(2D))

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Membrane Proteins

Background:

  • The small multi-drug resistant (SMR) transporter EmrE is a key protein involved in multidrug efflux.
  • Understanding EmrE's oligomeric state is crucial for elucidating its transport mechanism, but has been a subject of debate due to its small size.
  • Previous studies have yielded conflicting results regarding EmrE's functional oligomeric state.

Purpose of the Study:

  • To definitively determine the oligomeric state of the purified EmrE transporter.
  • To investigate how different membrane environments influence the dimerization affinity of EmrE.
  • To provide a stable model system for studying multidrug transporters.

Main Methods:

  • Purification of EmrE protein.
  • Dimerization studies using isotropic bicelles and dilauroylphosphatidylcholine (DLPC) liposomes.
  • Förster resonance energy transfer (FRET) measurements to quantify monomer-dimer equilibrium constants (KMD(2D)).

Main Results:

  • EmrE exists as a homodimer in isotropic bicelles, with a monomer-dimer equilibrium constant (KMD(2D)) of 0.002-0.009 mol%.
  • Dimer stability is significantly higher in bicelles compared to detergent micelles (KMD(2D) of 0.8-0.95 mol%).
  • In DLPC liposomes, EmrE dimerization is even tighter (KMD(2D) of 0.0005-0.0008 mol%), as determined by FRET.

Conclusions:

  • The homodimeric state of EmrE is confirmed across different membrane mimetics.
  • Lipid composition plays a critical role in stabilizing EmrE dimers, influencing its functional oligomeric state.
  • These findings underscore the importance of considering the lipid environment when studying membrane protein structure and function.