2.A.55 The Metal Ion (Mn2+-iron) Transporter (Nramp) Family

Homologues of this family are found in various yeasts, plants, animals, archaea, and Gram-negative and Gram-positive bacteria termed ''natural resistance-associated'' macrophage protein (NRAMP) proteins because one of the animal homologues plays a role in resistance to intracellular bacterial pathogens such as Salmonella enterica serovar Typhimurium, Leishmania donovani and Mycobacterium bovis. The natural history of SLC11 genes in vertebrates has been discussed by Neves et al. (2011). Proposed to be a distant member of the DMT Superfamily (TC# 2.A.7), several human pathologies may result from defects in Nramp-dependent Fe2+ or Mn2+ transport, including iron overload, neurodegenerative diseases and innate susceptibility to infectious diseases (Cellier 2012).

Humans and rodents possess two distinct NRAMPs. The broad specificity NRAMP2 (DMT1), which transports a range of divalent metal cations, transports Fe2+  and H+ with a 1:1 stoichiometry and apparent affinities of 6 μm and about 1 μm, respectively. Variable H+:Fe2+  stoichiometry has also been reported. The order of substrate preference for NRAMP2 is Fe2+> Zn2+> Mn2+> Co2+> Ca2+> Cu2+> Ni2+> Pb2+. Many of these ions can inhibit iron absorption. Mutation of Nramp2 in rodents leads to defective endosomal iron export within the ferritin cycle, impaired intestinal iron absorption and microcytic anemia. Symptoms of Mn2+ deficiency are also seen. It is found in apical membranes of intestinal epithelial cells but also in late endosomes and lysosomes.

In contrast to the widely expressed NRAMP2, NRAMP1 is expressed primarily in macrophages and monocytes and appears to have a preference for Mn2+ rather than Fe2+. NRAMP1 (TC# 2.A.55.2.3) has been reported to function by metal:H+ antiport (Techau et al., 2007). It is hypothesized that a deficiency for Mn2+ or some other metal prevents the generation of reactive oxygenic and nitrogenic compounds that are used by macrophage to combat pathogens. This hypothesis is supported by studies on the bacterial NRAMP homologues which exhibit extremely high selectivity for Mn2+ over Fe2+, Zn2+ and other divalent cations. Regulation of these transporters in bacteria can occur through Fur, OxyR, and most commonly a DtxR homolog, MntR.

The Smf1 protein of Saccharomyces cerevisiae appears to catalyze high-affinity (Km = 0.3 μm) Mn2+ uptake while the closely related Smf2 protein may catalyze low affinity (Km = 60 μm) Mn2+ uptake in the same organism. Both proteins also mediate H+-dependent Fe2+ uptake. These proteins are of 575 and 549 amino acyl residues in length and are predicted to have 8-12 transmembrane α-helical spanners. The E. coli homologue of 412 aas exhibits 11 putative and confirmed TMSs with the N-terminus in and the C-terminus out. The yeast proteins may be localized to the vacuole and/or the plasma membrane of the yeast cell. Indirect and some direct experiments suggest that they may be able to transport several heavy metals including Mn2+, Cu2+, Cd2+ and Co2+. A third yeast protein, Smf3p, appears to be exclusively intracellular, possibly in the Golgi. Nramp2 (Slc11A2) of Homo sapiens (TC #2.A.55.2.1) has a 12 TMS topology with intracellular N- and C-termini. Two-fold structural symmetry in the arrangement of membrane helices for TM1-5 and TM6-10 (conserved Slc2 hydrophobic core) is suggested (Czachorowski et al., 2009). 

The Nramp family of divalent metal transporters enables manganese import in bacteria and dietary iron uptake in mammals. Bozzi et al. 2016 determined the crystal structure of the Deinococcus radiodurans Nramp homolog (DraNramp) in an inward-facing apo state, including the complete transmembrane (TM) segment 1a (absent from a previous Nramp structure). Cysteine accessibility scanning results Allowed identification of the metal-permeation pathway in the alternate outward-open conformation. Two natural anemia-causing glycine-to-arginine mutations impaired transition metal transport in both human Nramp2 and DraNramp. The TM4 G153R mutation perturbs the closing of the outward metal-permeation pathway and alters the selectivity of the conserved metal-binding site. In contrast, the TM1a G45R mutation prevents conformational change by sterically blocking the essential movement of that helix, thus locking the transporter in an inward-facing state (Bozzi et al. 2016).

The generalized transport reaction catalyzed by Nramp family proteins is:

Me2+ (out) H+ (out) ⇌ Me2+ (in) H+ (in)



This family belongs to the APC Superfamily.

 

References:

Au, C., A. Benedetto, J. Anderson, A. Labrousse, K. Erikson, J.J. Ewbank, and M. Aschner. (2009). SMF-1, SMF-2 and SMF-3 DMT1 orthologues regulate and are regulated differentially by manganese levels in C. elegans. PLoS One 4: e7792.

Bai, S.P., L. Lu, X.G. Luo, and B. Liu. (2008). Cloning, sequencing, characterization, and expressions of divalent metal transporter one in the small intestine of broilers. Poult Sci 87: 768-776.

Bardou-Jacquet, E., M.L. Island, A.M. Jouanolle, L. Détivaud, N. Fatih, M. Ropert, E. Brissot, A. Mosser, H. Maisonneuve, P. Brissot, and O. Loréal. (2011). 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. Blood Cells Mol Dis 47: 243-248.

Beaumont, C., J. Delaunay, G. Hetet, B. Grandchamp, M. de Montalembert, and G. Tchernia. (2006). Two new human DMT1 gene mutations in a patient with microcytic anemia, low ferritinemia, and liver iron overload. Blood 107: 4168-4170.

Bozzi, A.T., L.B. Bane, W.A. Weihofen, A. Singharoy, E.R. Guillen, H.L. Ploegh, K. Schulten, and R. Gaudet. (2016). Crystal Structure and Conformational Change Mechanism of a Bacterial Nramp-Family Divalent Metal Transporter. Structure. [Epub: Ahead of Print]

Cailliatte R., Schikora A., Briat JF., Mari S. and Curie C. (2010). High-affinity manganese uptake by the metal transporter NRAMP1 is essential for Arabidopsis growth in low manganese conditions. Plant Cell. 22(3):904-17.

Cellier, M.F. (2012). Nramp: from sequence to structure and mechanism of divalent metal import. Curr Top Membr 69: 249-293.

Chen, S.L., Y.X. Zhang, J.Y. Xu, L. Meng, Z.X. Sha, and G.C. Ren. (2007). Molecular cloning, characterization and expression analysis of natural resistance associated macrophage protein (Nramp) cDNA from turbot (Scophthalmus maximus). Comp Biochem Physiol B Biochem Mol Biol 147: 29-37.

Chen, X.-Z., J.-B. Peng, A. Cohen, H. Nelson, N. Nelson, and M.A. Hediger. (1999). Yeast SMF1 mediates H+-coupled iron uptake with concomitant uncoupled cation currents. J. Biol. Chem. 274: 35089-35094.

Cheng, X. and H. Wang. (2012). Multiple targeting motifs direct NRAMP1 into lysosomes. Biochem. Biophys. Res. Commun. 419: 578-583.

Chua, A.C. and E.H. Morgan. (1997). Manganese metabolism is impaired in the Belgrade laboratory rat. J Comp Physiol [B] 167: 361-369.

Cohen, A., H. Nelson, and N. Nelson. (2000). The family of SMF metal ion transporters in yeast cells. J. Biol. Chem. 275: 33388-33394.

Courville, P., R. Chaloupka, F. Veyrier, and M.F.M. Cellier. (2004). Determination of transmembrane topology of the Escherichia coli natural resistance-associated macrophage protein (Nramp) ortholog. J. Biol. Chem. 279: 3318-3326.

Culotta, V.C., M. Yang, and M.D. Hall. (2005). Manganese transport and trafficking: lessons learned from Saccharomyces cerevisiae. Eukaryot. Cell 4: 1159-1165.

Czachorowski M., Lam-Yuk-Tseung S., Cellier M. and Gros P. (2009). Transmembrane topology of the mammalian Slc11a2 iron transporter. Biochemistry. 48(35):8422-34.

Ding D., Salvi R. and Roth JA. (2014). Cellular localization and developmental changes of the different isoforms of divalent metal transporter 1 (DMT1) in the inner ear of rats. Biometals. 27(1):125-34.

Eide, D. and M.L. Guerinot. (1997). Metal ion uptake in eukaryotes. ASM News 63: 199-205.

Fleming, M.D., C.C.I. Trenor, M.A. Su, D. Foernzler, D.R. Beier, W.F. Dietrich, and N.C. Andrews. (1997). Microcytic anaemia mice have a mutation in Nramp2, a candidate iron transporter gene. Nat. Genet. 16: 383-386.

Fleming, M.D., M.A. Romano, M.A. Su, L.M. Garrick, M.D. Garrick, and N.C. Andrews. (1998). Nramp2 is mutated in the anemic Belgrade (b) rat: evidence of a role for Nramp2 in endosomal iron transport. Proc. Natl. Acad. Sci. USA 95: 1148-1153.

Garrick, M.D., K.G. Dolan, C. Horbinski, A.J. Ghio, D. Higgins, M. Porubcin, E.G. Moore, L.N. Hainsworth, J.N. Umbreit, M.E. Conrad, L. Feng, A. Lis, J.A. Roth, S. Singleton, and L.M. Garrick. (2003). DMT1: a mammalian transporter for multiple metals. Biometals 16: 41-54.

Gunshin, H., B. Mackenzie, U.V. Berger, Y. Gunshin, M.F. Romero, W.F. Boron, S. Nussberger, J.L. Gollan, and M.A. Hediger. (1997). Cloning and characterization of a mammalian proton-coupled metal-ion transporter. Nature 388: 482-488.

Haemig, H.A., P.J. Moen, and R.J. Brooker. (2010). Evidence that highly conserved residues of transmembrane segment 6 of Escherichia coli MntH are important for transport activity. Biochemistry 49: 4662-4671.

Hohle, T.H. and M.R. O'Brian. (2009). The mntH gene encodes the major Mn2+ transporter in Bradyrhizobium japonicum and is regulated by manganese via the Fur protein. Mol. Microbiol. 72: 399-409.

Hug, L.A., B.J. Baker, K. Anantharaman, C.T. Brown, A.J. Probst, C.J. Castelle, C.N. Butterfield, A.W. Hernsdorf, Y. Amano, K. Ise, Y. Suzuki, N. Dudek, D.A. Relman, K.M. Finstad, R. Amundson, B.C. Thomas, and J.F. Banfield. (2016). A new view of the tree of life. Nat Microbiol 1: 16048.

Karlinsey, J.E., M.E. Maguire, L.A. Becker, M.L. Crouch, and F.C. Fang. (2010). The phage shock protein PspA facilitates divalent metal transport and is required for virulence of Salmonella enterica sv. Typhimurium. Mol. Microbiol. 78: 669-685.

Kehres, D.G., A. Janakiraman, J.M. Slauch, and M.E. Maguire. (2002). Regulation of Salmonella enterica serovar Typhimurium mntH transcription by H2O2, Fe2+, and Mn2+. J. Bacteriol. 184: 3151-3158.

Kehres, D.G., M.L. Zaharik, B.B. Finlay, and M.E. Maguire. (2000). The NRAMP proteins of Salmonella typhimurium and Escherichia coli are selective manganese transporters involed in the response to reactive oxygen. Mol. Microbiol. 36: 1085-1100.

Kwong, R.W., J.A. Andrés, and S. Niyogi. (2010). Molecular evidence and physiological characterization of iron absorption in isolated enterocytes of rainbow trout (Oncorhynchus mykiss): implications for dietary cadmium and lead absorption. Aquat Toxicol 99: 343-350.

Lane, D.J. and D.R. Richardson. (2014). Chaperone turns gatekeeper: PCBP2 and DMT1 form an iron-transport pipeline. Biochem. J. 462: e1-3.

Lanquar, V., F. Lelièvre, S. Bolte, C. Hamès, C. Alcon, D. Neumann, G. Vansuyt, C. Curie, A. Schröder, U. Krämer, H. Barbier-Brygoo, and S. Thomine. (2005). Mobilization of vacuolar iron by AtNRAMP3 and AtNRAMP4 is essential for seed germination on low iron. EMBO. J. 24: 4041-4051.

Lanquar, V., M.S. Ramos, F. Lelièvre, H. Barbier-Brygoo, A. Krieger-Liszkay, U. Krämer, and S. Thomine. (2010). Export of vacuolar manganese by AtNRAMP3 and AtNRAMP4 is required for optimal photosynthesis and growth under manganese deficiency. Plant Physiol. 152: 1986-1999.

Li, J., L. Wang, L. Wang, and F. Li. (2012). Structure and transmembrane topology of slc11a1 TMD1-5 in lipid membranes. Biopolymers 98: 224-233.

Lin, Z., J.A. Fernández-Robledo, M.F. Cellier, and G.R. Vasta. (2011). The natural resistance-associated macrophage protein from the protozoan parasite Perkinsus marinus mediates iron uptake. Biochemistry 50: 6340-6355.

Makui, H., E. Roig, S.T. Cole, J.D. Helmann, P. Gros, and M.F.M. Cellier. (2000). Identification of the Escherichia coli K-12 Nramp orthologue (MntH) as a selective divalent metal ion transporter. Mol. Microbiol. 35: 1065-1078.

Mani, A. and K. Sankaranarayanan. (2018). In Silico Analysis of Natural Resistance-Associated Macrophage Protein (NRAMP) Family of Transporters in Rice. Protein J 37: 237-247.

Mizuno, T., K. Usui, K. Horie, S. Nosaka, N. Mizuno, and H. Obata. (2005). Cloning of three ZIP/Nramp transporter genes from a Ni hyperaccumulator plant Thlaspi japonicum and their Ni2+-transport abilities. Plant Physiol. Biochem 43: 793-801.

Nam H., Wang CY., Zhang L., Zhang W., Hojyo S., Fukada T. and Knutson MD. (2013). ZIP14 and DMT1 in the liver, pancreas, and heart are differentially regulated by iron deficiency and overload: implications for tissue iron uptake in iron-related disorders. Haematologica. 98(7):1049-57.

Neves, J.V., J.M. Wilson, H. Kuhl, R. Reinhardt, L.F. Castro, and P.N. Rodrigues. (2011). Natural history of SLC11 genes in vertebrates: tales from the fish world. BMC Evol Biol 11: 106.

Nevo, Y. (2007). Site-directed mutagenesis investigation of coupling properties of metal ion transport by DCT1. Biochim. Biophys. Acta. 1778(1):334-341.

Patzer, S.I. and K. Hantke. (2001). Dua1 repression by Fe2+-Fur and Mn2+-MntR of the mntH gene, encoding an NRAMP-like Mn2+ transporter in Escherichia coli. J. Bacteriol. 183: 4806-4813.

Peracino, B., C. Wagner, A. Balest, A. Balbo, B. Pergolizzi, A.A. Noegel, M. Steinert, and S. Bozzaro. (2006). Function and mechanism of action of Dictyostelium Nramp1 (Slc11a1) in bacterial infection. Traffic 7: 22-38.

Peracino, B., S. Buracco, and S. Bozzaro. (2013). The Nramp (Slc11) proteins regulate development, resistance to pathogenic bacteria and iron homeostasis in Dictyostelium discoideum. J Cell Sci 126: 301-311.

Picard, V., G. Govoni, N. Jabado, and P. Gros. (2000). Nramp 2 (DCT1/DMT1) expressed at the plasma membrane transports iron and other divalent cations into a calcein-accessible cytoplasmic pool. J. Biol. Chem. 275: 35738-35745.

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

Portnoy, M.E., X.F. Liu, and V.C. Culotta. (2000). Saccharomyces cerevisiae expresses three functionally distinct homologues of the NRAMP family of metal transporters. Mol. Cell Biol. 20: 7893-7902.

Que, Q. and J.D. Helmann. (2000). Manganese homeostasis in Bacillus subtilis is regulated by MntR, a bifunctional regulator related to the diphtheria toxin repressor family of proteins. Mol. Microbiol. 35: 1454-1468.

Rose, P.P., S.L. Hanna, A. Spiridigliozzi, N. Wannissorn, D.P. Beiting, S.R. Ross, R.W. Hardy, S.A. Bambina, M.T. Heise, and S. Cherry. (2011). Natural resistance-associated macrophage protein is a cellular receptor for sindbis virus in both insect and mammalian hosts. Cell Host Microbe 10: 97-104.

Stimpson, H.E., M.J. Lewis, and H.R. Pelham. (2006). Transferrin receptor-like proteins control the degradation of a yeast metal transporter. EMBO. J. 25: 662-672.

Supek, F., L. Supekova, H. Nelson, and N. Nelson. (1996). A yeast manganese transporter related to the macrophage protein involved in conferring resistance to mycobacteria. Proc. Natl. Acad. Sci. USA 93: 5105-5110.

Tabuchi, M., T. Yoshimori, K. Yamaguchi, T. Yoshida, and F. Kishi. (2000). Human NRAMP2/DMT1, which mediates iron transport across endosomal membranes, is localized to late endosomes and lysosomes in Hep-2 cells. J. Biol. Chem. 29: 22220-22228.

Techau, M.E., J. Valdez-Taubas, J.F. Popoff, R. Francis, M. Seaman, and J.M. Blackwell. (2007). Evolution of differences in transport function in slc11a family members. J. Biol. Chem. 282: 35646-35656.

Ueki, T., N. Furuno, and H. Michibata. (2011). A novel vanadium transporter of the Nramp family expressed at the vacuole of vanadium-accumulating cells of the ascidian Ascidia sydneiensis samea. Biochim. Biophys. Acta. 1810: 457-464.

VanDuyn, N., R. Settivari, J. LeVora, S. Zhou, J. Unrine, and R. Nass. (2013). The metal transporter SMF-3/DMT-1 mediates aluminum-induced dopamine neuron degeneration. J Neurochem 124: 147-157.

Vatansever, R., E. Filiz, and I.I. Ozyigit. (2016). In silico analysis of Mn transporters (NRAMP1) in various plant species. Mol Biol Rep 43: 151-163.

Wang, D., Y. Song, J. Li, C. Wang, and F. Li. (2011). Structure and metal ion binding of the first transmembrane domain of DMT1. Biochim. Biophys. Acta. 1808: 1639-1644.

Wei YF., Li T., Li LF., Wang JL., Cao GH. and Zhao ZW. (2016). Functional and transcript analysis of a novel metal transporter gene EpNramp from a dark septate endophyte (Exophiala pisciphila). Ecotoxicol Environ Saf. 124:363-8.

Wei, W., T. Chai, Y. Zhang, L. Han, J. Xu, and Z. Guan. (2009). The Thlaspi caerulescens NRAMP homologue TcNRAMP3 is capable of divalent cation transport. Mol Biotechnol 41: 15-21.

Wessling-Resnick, M. (2000). Iron transport. Annu. Rev. Nutr. 20: 129-151.

West, A.H., D.J. Clark, J. Martin, W. Neupert, F.-U. Hartl, and A.L. Horwich. (1992). Two related genes encoding extremely hydrophobic proteins suppress a lethal mutation in the yeast mitochondrial processing enhancing protein. J. Biol. Chem. 267: 24625-24633.

Xia, J., N. Yamaji, and J.F. Ma. (2011). Further characterization of an aluminum influx transporter in rice. Plant Signal Behav 6: 160-163.

Xia, J., N. Yamaji, T. Kasai, and J.F. Ma. (2010). Plasma membrane-localized transporter for aluminum in rice. Proc. Natl. Acad. Sci. USA 107: 18381-18385.

Xu, H., X. Liu, J. Xia, T. Yu, Y. Qu, H. Jiang, and J. Xie. (2018). Activation of NMDA receptors mediated iron accumulation via modulating iron transporters in Parkinson''s disease. FASEB J. fj201800060RR. [Epub: Ahead of Print]

Examples:

TC#NameOrganismal TypeExample
2.A.55.1.1

High-affinity Me2+ (Fe2+, Mn2+, Zn2+, Cu2+, Cd2+, Ni2+, Co2+) uptake transporter, Smf1p or ESP1p of 575 aas and 11 TMSs.  Important for oxidative stress protection. Its activity is regulated by the Tre1 protein alone, and it's degradation is dependent on the Bsd2, Rsp5, Tre1 and Tre2 proteins (Stimpson et al. 2006).

Eukaryotes, bacteria, archaea

Smf1p of Saccharomyces cerevisiae

 
2.A.55.1.2

Low-affinity Me2+ (Mn2+, Cu2+) uptake transporter, Smf2p.  Essential for manganese uptake.

Eukaryotes, bacteria, archaea

Smf2p of Saccharomyces cerevisiae

 
2.A.55.1.3Intracellular (Golgi?) heavy metal transporter, Smf3p Yeast Smf3p of Saccharomyces cerevisiae (NP_013134)
 
2.A.55.1.4

Manganese transporter Pdt1

Yeast

Pdt1 of Schizosaccharomyces pombe

 
2.A.55.1.5

Plasma membrane NRAMP divalent cation (Fe2+ and Cd2+ demonstrated) uptake system of 571 aas and 11 TMSs.  Cd2+ down regluates expression (Wei et al. 2015).

NRAMP of Exophiala pisciphila

 
Examples:

TC#NameOrganismal TypeExample
2.A.55.2.1

Heavy metal (Fe2+, Zn2+, Mn2+, Cu2+, Cd2+, Co2+, Ni2+ and Pb2+) ion:H+ symporter, Nramp2 or divalent metal transporter, DMT1 (Garrick et al. 2003). A 12 TMS topology with intracellular N- and C- termini is established. Two-fold structural symmetry in the arrangement of membrane helices for TM1-5 and TM6-10 (conserved Slc11 hydrophobic core) is suggested (Czachorowski et al., 2009).  A conserved motif in a central flexible region of TMS1 (DPGN) binds the metal ion (Wang et al. 2011).  Upregulated by iron deficiency and downregulated by iron loading (Nam et al. 2013).  NRAMP2 also serves as the Sindbis alpha virus receptor (Rose et al. 2011).  DMT1 interacts with the iron chaparone protein, PCBP2 (Q15366), in an iron-dependent fashion, and may be essential for iron uptake (Lane and Richardson 2014). Mutations cause a syndrome of congenital microcytic hypochromic anemia, poorly responsive to oral iron treatment, with liver iron overload associated paradoxically with normal to moderately elevated serum ferritin levels (Beaumont et al. 2006). Nigral iron accumulation and activation of NMDA receptors (NRs) contribute to the neurodegeneration of dopamine (DA) neurons in Parkinson's disease (PD), and activation of NRs participates in iron metabolism in the hippocampus (Xu et al. 2018). NR inhibitors MK-801 and AP5 protect nigrostriatal projection systems and reduce nigral iron levels. NMDA treatment increased the expression of DMT1 and decreased the expression of the iron exporter ferroportin 1 (Fpn1) (TC# 2.A.100.1.4) (Xu et al. 2018).

Animals

DMT1 (SLC11A2) of Homo sapiens

 
2.A.55.2.10

NRAMP2 (SLC11a2) of 552 aas and 10 TMSs.  Inovoled in iron hoemeostasis and infectivity together with NRAMP1 (TC#2.A.55.2.9).  Present in the contractile vacuole which regulates osmolarity and possible stores iron (Peracino et al. 2013).

Slime molds

NRAMP2 of Dictyostelium discoideum

 
2.A.55.2.11

NRAMP2 of 596 aas and 12 TMSs.  NRAMP2 also serves as the Sindbis alpha virus receptor (Rose et al. 2011).

Insects

NRAMP2 of Drosophila melanogaster

 
2.A.55.2.12

VO2+ (vanidate) NRAMP uptake system in vacuoles of vanadocytes (587 aas; Ueki et al. 2011).

Ascidians

Vanidate transporter of Ascidia sydneiensis samea (Vanadium-rich ascidian)


 
 
2.A.55.2.13


Enterocyte iron uptake system, NRAMP or DMT1 of 558 aas and 13 TMSs.  Inhibited by lead and cadmium ions competitively (Kwong et al. 2010). The close (85% identity) homologue from Scophthalmus maximus (Turbot) (Psetta maxima) has been characterized (Chen et al. 2007).

Animals

DMT1 of Oncorhynchus mykiss (Rainbow trout) (Salmo gairdneri)

 
2.A.55.2.14

NRAMP3 iron/cadmium transporter of 512 aas (Wei et al. 2009).

Plants

NRAMP3 of Noccaea caerulescens
 
2.A.55.2.15

Divalent cation and aluminum transporter, Smf3.  Mediates aluminum-induced dopamine neuron degeneration (VanDuyn et al. 2013).

Animals

Smf3 of Caenorhabditis elegans

 
2.A.55.2.16

Fe2+/Mn2+ transporter, Smf1 of 562 aas and 12 TMSs (Au et al. 2009).

Animals

Smf1 of Caenorhabditis elegans

 
2.A.55.2.17

DMT1, SLC11A2 or NRAMP2, isoform 1, of 564 aas and 12 TMSs. It is an electrogenic Mn2+ transporter  that is expressed at high levels in the brush-border membranes of enterocytes (Bai et al. 2008).

DMT1 of Gallus gallus (chicken)

 
2.A.55.2.18

NRAMP4 of 512 aas and 12 TMSs, a vacuolar metal transporter involved in intracellular metal homeostasis. It can transport iron (Fe), manganese (Mn) and cadmium (Cd), and regulates metal accumulation under Fe starvation. It acts redundantly with NRAMP3 (which is 85% identical to it) to mobilize vacuolar Fe and provide sufficient Fe during seed germination (Lanquar et al. 2005). In association with NRAMP3, it is required for optimal growth and photosynthesis under Mn deficiency. It exports Mn from vacuoles in leaf mesophyll cells, making Mn available for functional photosystem II in chloroplasts (Lanquar et al. 2010). Its ortholog in Thlaspi japonicum has been characterized (Mizuno et al. 2005).

NRAMP4 of Arabidopsis thaliana

 
2.A.55.2.2

Me2+ (Fe2+, Cd2+, Co2+):H+ symporter, DCT1 (Nramp2) (Splice variant isoforms serve different functions). The stoichiometry between metal ion and proton in the symport process catalyzed by DCT1 varies under different conditions due to mechanistic proton slip. A single reciprocal mutation, I144F, in TMS2 of DCT1 abolished the metal ion transport activity, increased the slip currents, and generated sodium slip currents (Nevo, 2007). A double mutation, adding F227I in TMS4 to I144F restored the uptake activity of DCT1 and reduced the slip currents. Thus, these regions are important in coupling metal ion and proton symport (Nevo, 2007).  NRAMP2 also serves as the Sindbis alpha virus receptor (Rose et al. 2011).  Three isoforms are expressed differentially in different cell types and are developmentally regulated (Ding et al. 2013).

Animals

DCT1 of Rattus norvegicus

 
2.A.55.2.3

Macrophage divalent cation (Mn2+ > Fe2+):H+ antiporter (catalyzes divalent cation efflux and regulates cation homeostasis), NRAMP1 or Slc11a2. (Techau et al., 2007). The G212V mutation leads to microcytic anemia and liver iron overload (Bardou-Jacquet et al., 2011). Multiple targeting motifs direct NRAMP1 into lysosomes (Cheng and Wang, 2012). The structure and topology has been studied revealing a symmetric but inversely oriented arrangement (Li et al., 2012).

AnimalsSLC11A1 of Homo sapiens
 
2.A.55.2.4

The major root plasma membrane high affinity Me2+(Fe2+ Co2+ Mn2+) uptake transporter, NRAMP-1 (stimulated by Mn2+ deficiency) (Cailliatte et al., 2010).  In silico analyses of plant NRAMPs have been performed  using NRAMP1 as the query sequence (Vatansever et al. 2016).

Plants

NRAMP-1 of Arabidopsis thaliana (Q9SAH8)

 
2.A.55.2.5

Nramp aluminum transporter 1, Nrat1; specific for trivalent Al ion in rice (Xia et al., 2010; Xia et al. 2011). There are 7 isoforms of NRAMPs in rice, and they transport a variety of metals, Zn2+, Mn2+, Fe2+, Cd2+, etc. (Mani and Sankaranarayanan 2018).

Plants

Nrat1 of Oryza sativa (Q6ZG85)

 
2.A.55.2.6

Mn2+ transporter, MntH (Hohle and O'Brian, 2009)

Bacteria 

MntH of Bradyrhizobium japonicum (Q89K67) 

 
2.A.55.2.7

Iron transporter, NRAMP isoform III (Lin et al., 2011).

Protozoa (Alveolata)

NRAMP isoform III of Perkinsus marinus (D5FGJ2)

 
2.A.55.2.8Ethylene-insensitive protein 2 (AtEIN2) (EIN-2) (Cytokinin-resistant protein AtCKR1)PlantsEIN2 of Arabidopsis thaliana
 
2.A.55.2.9

NRAMP1 (SLC11a1) of 533 aas and 11 TMSs.  Regulates iron homeostasis and bacterial infection; present in phagosomes and macroinosomes (Peracino et al. 2013).  Transports metal cations out of the phagolysosome, thereby depleting iron. Nramp1 overexpression protects cells from L. pneumophila infection (Peracino et al. 2006).

 

Slime molds

NRAMP1 of Dictyostelium discoideum

 
Examples:

TC#NameOrganismal TypeExample
2.A.55.3.1

Me2+ (Mn2+, Fe2+, Cd2+, Co2+, Zn2+, Ni2+):H+ symporter, MntH (Mn2+ · MntR and Fe2+ · Fur repressible). Specific resides in TMS1 and 6 line the pore and play a role in pH regulation (Courville et al., 2004; Haemig et al. 2010). Important for virulence in Salmonella (Karlinsey et al., 2010).

Bacteria

MntH (YfeP) of E. coli (P0A769)

 
2.A.55.3.2MntH homologue (20% I) of unknown functionBacteriaYcsG of Bacillus subtilis (P42964)
 
2.A.55.3.3Manganese transport protein MntHBacilliMntH of Bacillus subtilis
 
2.A.55.3.4

Actinobacteria

 
2.A.55.3.5

Uncharacterized permease of 406 aas

Proteobacteria

UP of Pseudomonas stutzeri

 
2.A.55.3.6

NRAMP homologue; putative manganese porter of 544 aas and 13 TMSs.

Proteobacteria

Mn2+ porter of Bradyrhizobium sp.

 
2.A.55.3.7

H+-stimulated, divalent metal cation uptake system, MntH of 436 aas and 11 TMSs. The x-ray structure has been determined, revealing the probable ion translocation pathway (Bozzi et al. 2016).

MntH of Deinococcus radiodurans

 
2.A.55.3.8

Uncharacterized protein of 465 aas and 11 TMSs (Hug et al. 2016).

UP of Candidatus Peribacter riflensis

 
2.A.55.3.9

NRAMP homologue of 483 aas and 11 TMSs in a 6 + 5 TMS arrangement.

NRAMP homologue of Saccharopolyspora erythraea