title: The gusBC genes of Escherichia coli encode a glucuronide transport system.
abstract: Two genes, gusB and gusC, from a natural fecal isolate of Escherichia coli are shown to encode proteins responsible for transport of beta-glucuronides with synthetic [(14)C]phenyl-1-thio-beta-d-glucuronide as the substrate. These genes are located in the gus operon downstream of the gusA gene on the E. coli genome, and their expression is induced by a variety of beta-d-glucuronides. Measurements of transport in right-side-out subcellular vesicles show the system has the characteristics of secondary active transport energized by the respiration-generated proton motive force. When the genes were cloned together downstream of the tac operator-promoter in the plasmid pTTQ18 expression vector, transport activity was increased considerably with isopropylthiogalactopyranoside as the inducer. Amplified expression of the GusB and GusC proteins enabled visualization and identification by N-terminal sequencing of both proteins, which migrated at ca. 32 kDa and 44 kDa, respectively. Separate expression of the GusB protein showed that it is essential for glucuronide transport and is located in the inner membrane, while the GusC protein does not catalyze transport but assists in an as yet unknown manner and is located in the outer membrane. The output of glucuronides as waste by mammals and uptake for nutrition by gut bacteria or reabsorption by the mammalian host is discussed.
authors.affiliation: Astbury Centre for Structural Molecular Biology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Wei-Jun
authors.initials: WJ
authors.lastname: Liang
authors.forename: Kate J
authors.initials: KJ
authors.lastname: Wilson
authors.forename: Hao
authors.initials: H
authors.lastname: Xie
authors.forename: Jan
authors.initials: J
authors.lastname: Knol
authors.forename: Shun'ichi
authors.initials: S
authors.lastname: Suzuki
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Rutherford
authors.forename: Peter J F
authors.initials: PJ
authors.lastname: Henderson
authors.forename: Richard A
authors.initials: RA
authors.lastname: Jefferson
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D020719:Glucuronides / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic
chemical_list: D029968:Escherichia coli Proteins; D020719:Glucuronides; C499989:GusB protein, E coli; C499990:GusC protein, E coli; D026901:Membrane Transport Proteins