title: The multidrug resistance efflux complex, EmrAB from Escherichia coli forms a dimer in vitro.
abstract: Tripartite efflux systems are responsible for the export of toxins across both the inner and outer membranes of gram negative bacteria. Previous work has indicated that EmrAB-TolC from Escherichia coli is such a tripartite system, comprised of EmrB an MFS transporter, EmrA, a membrane fusion protein and TolC, an outer membrane channel. The whole complex is predicted to form a continuous channel allowing direct export from the cytoplasm to the exterior of the cell. Little is known, however, about the interactions between the individual components of this system. Reconstitution of EmrA+EmrB resulted in co-elution of the two proteins from a gel filtration column indicating formation of the EmrAB complex. Electron microscopic single particle analysis of the reconstituted EmrAB complex revealed the presence of particles approximately 240x140A, likely to correspond to two EmrAB dimers in a back-to-back arrangement, suggesting the dimeric EmrAB form is the physiological state contrasting with the trimeric arrangement of the AcrAB-TolC system.
authors.affiliation: Division of Molecular Biosciences, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
authors.forename: Mikio
authors.initials: M
authors.lastname: Tanabe
authors.forename: Gerda
authors.initials: G
authors.lastname: Szakonyi
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Brown
authors.forename: Peter J F
authors.initials: PJ
authors.lastname: Henderson
authors.forename: Jon
authors.initials: J
authors.lastname: Nield
authors.forename: Bernadette
authors.initials: B
authors.lastname: Byrne
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D011487:Protein Conformation; D055503:Protein Multimerization
chemical_list: D001425:Bacterial Outer Membrane Proteins; C489681:EmrA protein, E coli; C539510:EmrB protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C073126:tolC protein, E coli