title: Coupling of remote alternating-access transport mechanisms for protons and substrates in the multidrug efflux pump AcrB.
abstract: Membrane transporters of the RND superfamily confer multidrug resistance to pathogenic bacteria, and are essential for cholesterol metabolism and embryonic development in humans. We use high-resolution X-ray crystallography and computational methods to delineate the mechanism of the homotrimeric RND-type proton/drug antiporter AcrB, the active component of the major efflux system AcrAB-TolC in Escherichia coli, and one most complex and intriguing membrane transporters known to date. Analysis of wildtype AcrB and four functionally-inactive variants reveals an unprecedented mechanism that involves two remote alternating-access conformational cycles within each protomer, namely one for protons in the transmembrane region and another for drugs in the periplasmic domain, 50 Å apart. Each of these cycles entails two distinct types of collective motions of two structural repeats, coupled by flanking α-helices that project from the membrane. Moreover, we rationalize how the cross-talk among protomers across the trimerization interface might lead to a more kinetically efficient efflux system.
authors.affiliation: Institute of Biochemistry, Goethe University, Frankfurt am Main, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Eicher
authors.affiliation: Institute of Physiology, University of Zurich, Zurich, Switzerland.
authors.forename: Markus A
authors.initials: MA
authors.lastname: Seeger
authors.affiliation: Theoretical Molecular Biophysics Section, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States.
authors.forename: Claudio
authors.initials: C
authors.lastname: Anselmi
authors.affiliation: Theoretical Molecular Biophysics Section, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States.
authors.forename: Wenchang
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Institute of Biochemistry, Goethe University, Frankfurt am Main, Germany.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Brandstätter
authors.affiliation: Institute of Physiology, University of Zurich, Zurich, Switzerland.
authors.forename: François
authors.initials: F
authors.lastname: Verrey
authors.affiliation: Department of Biology, University of Konstanz, Konstanz, Germany.
authors.forename: Kay
authors.initials: K
authors.lastname: Diederichs
authors.affiliation: Theoretical Molecular Biophysics Section, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States.
authors.forename: José D
authors.initials: JD
authors.lastname: Faraldo-Gómez
authors.affiliation: Institute of Biochemistry, Goethe University, Frankfurt am Main, Germany.
authors.forename: Klaas M
authors.initials: KM
authors.lastname: Pos
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D011336:Probability; D011401:Promoter Regions, Genetic; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011522:Protons; D012984:Software; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D029968:Escherichia coli Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011522:Protons; D014867:Water; C083496:AcrB protein, E coli
keywords: E. coli; H+ transport; antibiotic resistance; biochemistry; biophysics; drug resistance; drug transport; efflux pump; mechanistic coupling; structural biology