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 (DPNG 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].

1: Macrophage NRAMP1 and its role in resistance to microbial infections. Govoni G, Gros P; Inflamm Res 1998;47:277-284. PMID:9719491

2: Metal ion homeostasis and intracellular parasitism. Agranoff DD, Krishna S Mol Microbiol 1998;28:403-412. PMID:9632246

3: Functional complementation of the yeast divalent cation transporter family SMF by NRAMP2, a member of the mammalian natural resistance- associated macrophage protein family. Pinner E, Gruenheid S, Raymond M, Gros P; J Biol Chem 1997;272:28933-28938. PMID:9360964

4: Resistance to intracellular infections: comparative genomic analysis of Nramp. Cellier M, Belouchi A, Gros P; Trends Genet 1996;12:201-204. PMID:8928221

5: Nramp defines a family of membrane proteins. Cellier M, Prive G, Belouchi A, Kwan T, Rodrigues V, Chia W, Gros P; Proc Natl Acad Sci U S A 1995;92:10089-10093. PMID:7479731

6: Crystal structure of a SLC11 (NRAMP) transporter reveals the basis for transition-metal ion transport. Ehrnstorfer IA, Geertsma ER, Pardon E, Steyaert J, Dutzler R; Nat Struct Mol Biol. 2014;21:990-996. PMID:25326704

7: Structures in multiple conformations reveal distinct transition metal and proton pathways in an Nramp transporter. Bozzi AT, Zimanyi CM, Nicoludis JM, Lee BK, Zhang CH, Gaudet R; Elife. 2019; [Epub ahead of print] PMID:30714568

8: Transport of magnesium by a bacterial Nramp-related gene. Shin JH, Wakeman CA, Goodson JR, Rodionov DA, Freedman BG, Senger RS, Winkler WC; PLoS Genet. 2014;10:e1004429. PMID:24968120