title: The nitrite transport protein NirC from Salmonella typhimurium is a nitrite/proton antiporter.
abstract: In anaerobically grown bacteria, transport of nitrite is catalyzed by an integral membrane protein of the form ate-nitrite transporter family, NirC, which in Salmonella typhimurium plays a critical role in intracellular virulence. We present a functional characterization of the S. typhimurium nitrite transporter StmNirC in native membrane vesicles as well as purified and reconstituted into proteoliposomes. Using an electrophysiological technique based on solid supported membranes, we show nitrite induced translocation of negative charges into proteoliposomes reconstituted with purified StmNirC. These data demonstrate the electrogenicity of StmNirC and its substrate specificity for nitrite. Monitoring changes in ΔpH on everted membrane vesicles containing overexpressed StmNirC using acridine orange as a pH indicator we demonstrate that StmNirC acts as a secondary active transporter. It promotes low affinity transport of nitrite coupled to H(+) antiport with a pH independent profile in the pH range from 6 to 8. In addition to nitrite also nitrate is transported by StmNirC, but with reduced flux and complete absence of proton antiport activity. Taken together, these data suggest a bispecific anion selectivity of StmNirC with an ion specific transport mode. This may play a role in regulating nitrite transport under physiological conditions.
authors.affiliation: Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, D-60438 Frankfurt am Main, Germany.
authors.forename: Adriana
authors.initials: A
authors.lastname: Rycovska
authors.forename: Lina
authors.initials: L
authors.lastname: Hatahet
authors.forename: Klaus
authors.initials: K
authors.lastname: Fendler
authors.forename: Hartmut
authors.initials: H
authors.lastname: Michel
mesh_terms: D000165:Acridine Orange / Q000737:chemistry; D027321:Anion Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000502:physiology; D008081:Liposomes / Q000737:chemistry*; D009573:Nitrites / Q000737:chemistry* / Q000378:metabolism; D012486:Salmonella typhimurium / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D037521:Virulence Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D008081:Liposomes; C088104:NirC protein, Bacteria; D009573:Nitrites; D037521:Virulence Factors; D000165:Acridine Orange