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J Cell Sci September 1, 2015; 128 (17): 3304-16.

Dictyostelium Nramp1, which is structurally and functionally similar to mammalian DMT1 transporter, mediates phagosomal iron efflux.

Buracco S , Peracino B , Cinquetti R , Signoretto E , Vollero A , Imperiali F , Castagna M , Bossi E , Bozzaro S .

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.

PubMed ID: 26208637
PMC ID: PMC4582194
Article link: J Cell Sci

Species referenced: Xenopus
Genes referenced: gopc slc11a1 slc11a2 tbx2 tsc1 tyro3

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References [+] :
Bardou-Jacquet, A novel N491S mutation in the human SLC11A2 gene impairs protein trafficking and in association with the G212V mutation leads to microcytic anemia and liver iron overload. 2011, Pubmed