title: EmrE dimerization depends on membrane environment.
abstract: The small multi-drug resistant (SMR) transporter EmrE functions as a homodimer. Although the small size of EmrE would seem to make it an ideal model system, it can also make it challenging to work with. As a result, a great deal of controversy has surrounded even such basic questions as the oligomeric state. Here we show that the purified protein is a homodimer in isotropic bicelles with a monomer-dimer equilibrium constant (KMD(2D)) of 0.002-0.009mol% for both the substrate-free and substrate-bound states. Thus, the dimer is stabilized in bicelles relative to detergent micelles where the KMD(2D) is only 0.8-0.95mol% (Butler et al. 2004). In dilauroylphosphatidylcholine (DLPC) liposomes KMD(2D) is 0.0005-0.0008mol% based on Förster resonance energy transfer (FRET) measurements, slightly tighter than bicelles. These results emphasize the importance of the lipid membrane in influencing dimer affinity.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660S. Euclid Ave., Box 8231, St. Louis, MO 63110, USA. Electronic address: duttas@biochem.wustl.edu.
authors.forename: Supratik
authors.initials: S
authors.lastname: Dutta
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660S. Euclid Ave., Box 8231, St. Louis, MO 63110, USA. Electronic address: eamorris@wustl.edu.
authors.forename: Emma A
authors.initials: EA
authors.lastname: Morrison
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660S. Euclid Ave., Box 8231, St. Louis, MO 63110, USA. Electronic address: khenzler@biochem.wustl.edu.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Henzler-Wildman
mesh_terms: D017920:Antiporters / Q000378:metabolism*; D001692:Biological Transport; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism*; D008823:Micelles; D055503:Protein Multimerization
chemical_list: D017920:Antiporters; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D008081:Liposomes; D008563:Membrane Lipids; D008823:Micelles; C075436:EmrE protein, E coli
keywords: Analytical ultra centrifugation; EmrE; Förster resonance energy transfer; Membrane mimetic; Oligomerization; Two dimensional equilibrium constant (K(MD)(2D))