title: Transport of lipophilic carboxylates is mediated by transmembrane helix 2 in multidrug transporter AcrB.
abstract: The deployment of multidrug efflux pumps is a powerful defence mechanism for Gram-negative bacterial cells when exposed to antimicrobial agents. The major multidrug efflux transport system in Escherichia coli, AcrAB-TolC, is a tripartite system using the proton-motive force as an energy source. The polyspecific substrate-binding module AcrB uses various pathways to sequester drugs from the periplasm and outer leaflet of the inner membrane. Here we report the asymmetric AcrB structure in complex with fusidic acid at a resolution of 2.5 Å and mutational analysis of the putative fusidic acid binding site at the transmembrane domain. A groove shaped by the interface between transmembrane helix 1 (TM1) and TM2 specifically binds fusidic acid and other lipophilic carboxylated drugs. We propose that these bound drugs are actively displaced by an upward movement of TM2 towards the AcrB periplasmic porter domain in response to protonation events in the transmembrane domain.
authors.affiliation: Institute of Biochemistry, Goethe University Frankfurt, Max-von-Laue-Strasse 9, D-60438 Frankfurt am Main, Germany.|Institute of Biochemistry, Goethe University Frankfurt, Max-von-Laue-Strasse 9, D-60438 Frankfurt am Main, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Oswald
authors.affiliation: Institute of Biochemistry, Goethe University Frankfurt, Max-von-Laue-Strasse 9, D-60438 Frankfurt am Main, Germany.
authors.forename: Heng-Keat
authors.initials: HK
authors.lastname: Tam
authors.affiliation: Institute of Biochemistry, Goethe University Frankfurt, Max-von-Laue-Strasse 9, D-60438 Frankfurt am Main, Germany.
authors.forename: Klaas M
authors.initials: KM
authors.lastname: Pos
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001665:Binding Sites; D001692:Biological Transport / Q000502:physiology; D002264:Carboxylic Acids / Q000378:metabolism*; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005672:Fusidic Acid / Q000737:chemistry / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D008958:Models, Molecular; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D000072417:Protein Domains; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002264:Carboxylic Acids; D029968:Escherichia coli Proteins; D005672:Fusidic Acid; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D047090:beta-Lactams; C083496:AcrB protein, E coli