title: A single-component multidrug transporter of the major facilitator superfamily is part of a network that protects Escherichia coli from bile salt stress.
abstract: Resistance to high concentrations of bile salts in the human intestinal tract is vital for the survival of enteric bacteria such as Escherichia coli. Although the tripartite AcrAB-TolC efflux system plays a significant role in this resistance, it is purported that other efflux pumps must also be involved. We provide evidence from a comprehensive suite of experiments performed at two different pH values (7.2 and 6.0) that reflect pH conditions that E. coli may encounter in human gut that MdtM, a single-component multidrug resistance transporter of the major facilitator superfamily, functions in bile salt resistance in E. coli by catalysing secondary active transport of bile salts out of the cell cytoplasm. Furthermore, assays performed on a chromosomal ΔacrB mutant transformed with multicopy plasmid encoding MdtM suggested a functional synergism between the single-component MdtM transporter and the tripartite AcrAB-TolC system that results in a multiplicative effect on resistance. Substrate binding experiments performed on purified MdtM demonstrated that the transporter binds to cholate and deoxycholate with micromolar affinity, and transport assays performed on inverted vesicles confirmed the capacity of MdtM to catalyse electrogenic bile salt/H(+) antiport.
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, Medical Biology Centre, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7BL, UK.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Paul
authors.forename: Kamela O
authors.initials: KO
authors.lastname: Alegre
authors.forename: Scarlett R
authors.initials: SR
authors.lastname: Holdsworth
authors.forename: Matthew
authors.initials: M
authors.lastname: Rice
authors.forename: James A
authors.initials: JA
authors.lastname: Brown
authors.forename: Paul
authors.initials: P
authors.lastname: McVeigh
authors.forename: Sharon M
authors.initials: SM
authors.lastname: Kelly
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Law
mesh_terms: D017920:Antiporters / Q000378:metabolism*; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001647:Bile Acids and Salts / Q000378:metabolism* / Q000633:toxicity*; D004361:Drug Tolerance; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D008074:Lipoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism
chemical_list: D017920:Antiporters; D001425:Bacterial Outer Membrane Proteins; D001647:Bile Acids and Salts; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C574623:MdtM protein, E coli; C073126:tolC protein, E coli