title: Funnel-like hexameric assembly of the periplasmic adapter protein in the tripartite multidrug efflux pump in gram-negative bacteria.
abstract: Gram-negative bacteria expel diverse toxic chemicals through the tripartite efflux pumps spanning both the inner and outer membranes. The Escherichia coli AcrAB-TolC pump is the principal multidrug exporter that confers intrinsic drug tolerance to the bacteria. The inner membrane transporter AcrB requires the outer membrane factor TolC and the periplasmic adapter protein AcrA. However, it remains ambiguous how the three proteins are assembled. In this study, a hexameric model of the adapter protein was generated based on the propensity for trimerization of a dimeric unit, and this model was further validated by presenting its channel-forming property that determines the substrate specificity. Genetic, in vitro complementation, and electron microscopic studies provided evidence for the binding of the hexameric adapter protein to the outer membrane factor in an intermeshing cogwheel manner. Structural analyses suggested that the adapter covers the periplasmic region of the inner membrane transporter. Taken together, we propose an adapter bridging model for the assembly of the tripartite pump, where the adapter protein provides a bridging channel and induces the channel opening of the outer membrane factor in the intermeshing tip-to-tip manner.
authors: Department of Manufacturing Pharmacy, College of Pharmacy and Research Institute for Drug Development, Pusan National University, Busan 609-735, Republic of Korea.
authors: Yongbin
authors: Y
authors: Xu
authors: Minho
authors: M
authors: Lee
authors: Arne
authors: A
authors: Moeller
authors: Saemee
authors: S
authors: Song
authors: Bo-Young
authors: BY
authors: Yoon
authors: Hong-Man
authors: HM
authors: Kim
authors: So-Young
authors: SY
authors: Jun
authors: Kangseok
authors: K
authors: Lee
authors: Nam-Chul
authors: NC
authors: Ha
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000502:physiology*; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008074:Lipoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D033903:Periplasmic Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary
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; D033903:Periplasmic Proteins; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C073126:tolC protein, E coli