The natural resistance-associated macrophage protein (NRAMP) family consists of animal NRAMP1, NRAMP2, yeast proteins Smf1 and Smf2 and bacterial homologues [6-8]. The NRAMP family includes functional related proteins defined by a conserved hydrophob ...
The natural resistance-associated macrophage protein (NRAMP) family consists of animal NRAMP1, NRAMP2, yeast proteins Smf1 and Smf2 and bacterial homologues [6-8]. The NRAMP family includes functional related proteins defined by a conserved hydrophobic core of ten transmembrane domains [5]. These membrane proteins are divalent cation transporters which have a high degree of sequence conservation, particularly, the residues contributing to ion interaction are stongly conserved (DPGN and MPH motifs) [6,7]. NRAMP1 is an integral membrane protein expressed exclusively in cells of the immune system and is recruited to the membrane of a phagosome upon phagocytosis, where it plays an essential role in host defense against pathogens [1-6]. Mutations in NRAMP1 may genetically predispose an individual to susceptibility to diseases including leprosy and tuberculosis [1]. NRAMP2 (DMT1) is a multiple divalent cation transporter broadly expressed in the duodenum, kidney, brain, testis and placenta. It transports Fe2+, Mn2+ and Cd+2, whereas Zn2+ is a poor substrate. Ca+2 and Mg+2 are not transported, which is important because their high concentrations in duodenum, where NRAMP2 is expressed at high levels, would interfere with the absorption of Fe2+ [6]. It is the major transferrin-independent iron uptake system in mammals [1,6]. NRAMP related members of this family have substrate specificity for Mn2+ and/or Mg2+, such as the yeast proteins Smf1 and Smf2 [3] and a group of bacterial transporters (NrmT, for Nramp-related magnesium transporter) [8].
