title: Dictyostelium Nramp1, which is structurally and functionally similar to mammalian DMT1 transporter, mediates phagosomal iron efflux.
abstract: The Nramp (Slc11) protein family is widespread in bacteria and eukaryotes, and mediates transport of divalent metals across cellular membranes. The social amoeba Dictyostelium discoideum has two Nramp proteins. Nramp1, like its mammalian ortholog (SLC11A1), is recruited to phagosomal and macropinosomal membranes, and confers resistance to pathogenic bacteria. Nramp2 is located exclusively in the contractile vacuole membrane and controls, synergistically with Nramp1, iron homeostasis. It has long been debated whether mammalian Nramp1 mediates iron import or export from phagosomes. By selectively loading the iron-chelating fluorochrome calcein in macropinosomes, we show that Dictyostelium Nramp1 mediates iron efflux from macropinosomes in vivo. To gain insight in ion selectivity and the transport mechanism, the proteins were expressed in Xenopus oocytes. Using a novel assay with calcein, and electrophysiological and radiochemical assays, we show that Nramp1, similar to rat DMT1 (also known as SLC11A2), transports Fe(2+) and manganese, not Fe(3+) or copper. Metal ion transport is electrogenic and proton dependent. By contrast, Nramp2 transports only Fe(2+) in a non-electrogenic and proton-independent way. These differences reflect evolutionary divergence of the prototypical Nramp2 protein sequence compared to the archetypical Nramp1 and DMT1 proteins.
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano 10043, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Buracco
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano 10043, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Peracino
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Cinquetti
authors.affiliation: Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano, Via Trentacoste 2, Milano 20133, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Signoretto
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Vollero
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Imperiali
authors.affiliation: Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano, Via Trentacoste 2, Milano 20133, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Castagna
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Via J. H. Dunant 3, Varese 21100, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Bossi
authors.affiliation: Department of Clinical and Biological Sciences, University of Torino, AOU S. Luigi, Orbassano 10043, Italy salvatore.bozzaro@unito.it.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Bozzaro
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D004023:Dictyostelium / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D007501:Iron / Q000378:metabolism*; D010588:Phagosomes / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D000099173:Natural Resistance-associated Macrophage Protein 1; D000099236:Solute Carrier Family 11, Member 2
chemical_list: D027682:Cation Transport Proteins; D007501:Iron; D015800:Protozoan Proteins; D000099173:Natural Resistance-associated Macrophage Protein 1; D000099236:Solute Carrier Family 11, Member 2
keywords: Bacterial infection; DMT1; Iron homeostasis; Macropinocytosis; Nramp1; Nramp2