title: Mycobacterium tuberculosis expresses a novel pH-dependent divalent cation transporter belonging to the Nramp family.
abstract: Mammalian natural resistance-associated macrophage protein (Nramp) homologues are important determinants of susceptibility to infection by diverse intracellular pathogens including mycobacteria. Eukaryotic Nramp homologues transport divalent cations such as Fe(2+), Mn(2+), Zn(2+), and Cu(2+). Mycobacterium tuberculosis and Mycobacterium bovis (bacillus Calmette-Guérin [BCG]) also encode an Nramp homologue (Mramp). RNA encoding Mramp induces approximately 20-fold increases in (65)Zn(2+) and (55)Fe(2+) uptake when injected into Xenopus laevis oocytes. Transport is dependent on acidic extracellular pH and is maximal between pH 5.5 and 6.5. Mramp-mediated (65)Zn(2+) and (55)Fe(2+) transport is abolished by an excess of Mn(2+) and Cu(2+), confirming that Mramp interacts with a broad range of divalent transition metal cations. Using semiquantitative reverse transcription PCR, we show that Mramp mRNA levels in M. tuberculosis are upregulated in response to increases in ambient Fe(2+) and Cu(2+) between <1 and 5 microM concentrations and that this upregulation occurs in parallel with mRNA for y39, a putative metal-transporting P-type ATPase. Using a quantitative ratiometric PCR technique, we demonstrate a fourfold decrease in Mramp/y39 mRNA ratios from organisms grown in 5-70 microM Cu(2+). M. bovis BCG cultured axenically and within THP-1 cells also expresses mRNA encoding Mramp. Mramp exemplifies a novel prokaryotic class of metal ion transporter. Within phagosomes, Mramp and Nramp1 may compete for the same divalent cations, with implications for intracellular survival of mycobacteria.
authors.affiliation: Department of Infectious Diseases, St. George's Hospital Medical School, London SW17 ORE, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Agranoff
authors.forename: I M
authors.initials: IM
authors.lastname: Monahan
authors.forename: J A
authors.initials: JA
authors.lastname: Mangan
authors.forename: P D
authors.initials: PD
authors.lastname: Butcher
authors.forename: S
authors.initials: S
authors.lastname: Krishna
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D027682:Cation Transport Proteins; D002413:Cations, Divalent / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D017136:Ion Transport; D033862:Iron-Binding Proteins; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis; D000099173:Natural Resistance-associated Macrophage Protein 1; D000099236:Solute Carrier Family 11, Member 2
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D002413:Cations, Divalent; D017931:DNA Primers; D033862:Iron-Binding Proteins; D008565:Membrane Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D000099173:Natural Resistance-associated Macrophage Protein 1; D000099236:Solute Carrier Family 11, Member 2