title: Structure of the tripartite multidrug efflux pump AcrAB-TolC suggests an alternative assembly mode.
abstract: Escherichia coli AcrAB-TolC is a multidrug efflux pump that expels a wide range of toxic substrates. The dynamic nature of the binding or low affinity between the components has impeded elucidation of how the three components assemble in the functional state. Here, we created fusion proteins composed of AcrB, a transmembrane linker, and two copies of AcrA. The fusion protein exhibited acridine pumping activity, suggesting that the protein reflects the functional structure in vivo. To discern the assembling mode with TolC, the AcrBA fusion protein was incubated with TolC or a chimeric protein containing the TolC aperture tip region. Three-dimensional structures of the complex proteins were determined through transmission electron microscopy. The overall structure exemplifies the adaptor bridging model, wherein the funnel-like AcrA hexamer forms an intermeshing cogwheel interaction with the α-barrel tip region of TolC, and a direct interaction between AcrB and TolC is not allowed. These observations provide a structural blueprint for understanding multidrug resistance in pathogenic Gram-negative bacteria.
authors.affiliation: Department of Manufacturing Pharmacy, Pusan National University, Busan 609-735, Korea.
authors.forename: Jin-Sik
authors.initials: JS
authors.lastname: Kim
authors.affiliation: Division of Electron Microscopic Research, Korea Basic Science Institute, Dajeon 169-148, Korea.
authors.forename: Hyeongseop
authors.initials: H
authors.lastname: Jeong
authors.affiliation: Department of Food and Animal Biotechnology, Department of Agricultural Biotechnology, Center for Food and Bioconvergence, Research Institute for Agricultural and Life Sciences, Seoul National University, Seoul 151-742, Korea.|Department of Life Science, Chung-Ang University, Seoul 156-756, Korea.
authors.forename: Saemee
authors.initials: S
authors.lastname: Song
authors.affiliation: Division of Magnetic Resonance, Korea Basic Science Institute, Chungbuk 363-883, Korea.
authors.forename: Hye-Yeon
authors.initials: HY
authors.lastname: Kim
authors.affiliation: Department of Life Science, Chung-Ang University, Seoul 156-756, Korea.
authors.forename: Kangseok
authors.initials: K
authors.lastname: Lee
authors.affiliation: Division of Electron Microscopic Research, Korea Basic Science Institute, Dajeon 169-148, Korea.
authors.forename: Jaekyung
authors.initials: J
authors.lastname: Hyun
authors.affiliation: Department of Food and Animal Biotechnology, Department of Agricultural Biotechnology, Center for Food and Bioconvergence, Research Institute for Agricultural and Life Sciences, Seoul National University, Seoul 151-742, Korea.
authors.forename: Nam-Chul
authors.initials: NC
authors.lastname: Ha
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D008074:Lipoproteins / Q000737:chemistry* / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011993:Recombinant Fusion Proteins; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C073126:tolC protein, E coli
keywords: complex structure; electron microscopy; membrane protein; multidrug efflux pump