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Two isoforms of a divalent metal transporter (DMT1) in Schistosoma mansoni suggest a surface-associated pathway for iron absorption in schistosomes.

ABSTRACT: We describe two homologues of the mammalian divalent metal transporter (DMT1) for Schistosoma mansoni, a pathogenic intravascular parasite of humans. Schistosomes have a high nutritional and metabolic demand for iron. Nucleotide sequences of the parasite homologues, designated SmDMT1A and -B, are identical in all but the 5'-regions. The predicted amino acid sequences share at least 60% identity with DMT1 (=Nramp2) of humans, mice, and rats, and at least 55% identity with Nramp1 from mice, humans and Caenorhabditis elegans. SmDMT1A is expressed in differentiating eggs, miracidia, cercariae, schistosomula, and adults, whereas SmDMT1B is expressed in all but the miracidium and occurs at lower levels than SmDMT1A in differentiating eggs and cercariae. An iron-responsive element, present at the 3'-untranslated region of many DMT1 molecules, is not present in schistosome mRNAs studied here. A Western blot analysis of adult worm preparations using a homologous rabbit serum raised against a schistosome DMT1 peptide and a heterologous serum raised against mammalian DMT1, revealed a band approximating 115 kDa. By immunofluorescence microscopy, the schistosome DMT1s localize primarily to the tegument. Iron uptake assays demonstrated that SmDMT1s were able to rescue yeast growth in ferrous iron-transport deficient yeast (fet3fet4). The results suggest that schistosomes express molecules for ferrous iron transport in their tegument, suggesting trans-tegumental transport as one means of iron acquisition for these parasites.

SUBMITTER: Smyth DJ

PROVIDER: S-EPMC1459476 | biostudies-literature | 2006 Jan

REPOSITORIES: biostudies-literature

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Two isoforms of a divalent metal transporter (DMT1) in Schistosoma mansoni suggest a surface-associated pathway for iron absorption in schistosomes.

Smyth Danielle J DJ Glanfield Amber A McManus Donald P DP Hacker Elke E Blair David D Anderson Greg J GJ Jones Malcolm K MK

The Journal of biological chemistry 20051102 4

We describe two homologues of the mammalian divalent metal transporter (DMT1) for Schistosoma mansoni, a pathogenic intravascular parasite of humans. Schistosomes have a high nutritional and metabolic demand for iron. Nucleotide sequences of the parasite homologues, designated SmDMT1A and -B, are identical in all but the 5'-regions. The predicted amino acid sequences share at least 60% identity with DMT1 (=Nramp2) of humans, mice, and rats, and at least 55% identity with Nramp1 from mice, humans ...[more]

PMID: 16267047

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Project description:Lymphatic filariasis and onchocerciasis are neglected parasitic diseases which pose a threat to public health in tropical and sub-tropical regions. Strategies for control and elimination of these diseases by mass drug administration (MDA) campaigns are designed to reduce symptoms of onchocerciasis and transmission of both parasites to eventually eliminate the burden on public health. Drugs used for MDA are predominantly microfilaricidal, and prolonged rounds of treatment are required for eradication. Understanding parasite biology is crucial to unravelling the complex processes involved in host-parasite interactions, disease transmission, parasite immune evasion, and the emergence of drug resistance. In nematode biology, large gaps still exist in our understanding of iron metabolism, iron-dependent processes and their regulation. The acquisition of iron from the host is a crucial determinant of the success of a parasitic infection. Here we identify a filarial ortholog of Divalent Metal Transporter 1 (DMT1), a member of a highly conserved family of NRAMP proteins that play an essential role in the transport of ferrous iron in many species. We cloned and expressed the B. malayi NRAMP ortholog in the iron-deficient fet3fet4 strain of Saccharomyces cerevisiae, performed qPCR to estimate stage-specific expression, and localized expression of this gene by immunohistochemistry. Results from functional iron uptake assays showed that expression of this gene in the iron transport-deficient yeast strain significantly rescued growth in low-iron medium. DMT1 was highly expressed in adult female and male B. malayi and Onchocerca volvulus. Immunolocalization revealed that DMT1 is expressed in the intestinal brush border, lateral chords, and reproductive tissues of males and females, areas also inhabited by Wolbachia. We hypothesize based on our results that DMT1 in B. malayi functions as an iron transporter. The presence of this transporter in the intestine supports the hypothesis that iron acquisition by adult females requires oral ingestion and suggests that the intestine plays a functional role in at least some aspects of nutrient uptake.

Project description:DMT1 (divalent metal-ion transporter 1) is a widely expressed metal-ion transporter that is vital for intestinal iron absorption and iron utilization by most cell types throughout the body, including erythroid precursors. Mutations in DMT1 cause severe microcytic anaemia in animal models. Four DMT1 isoforms that differ in their N- and C-termini arise from mRNA transcripts that vary both at their 5'-ends (starting in exon 1A or exon 1B) and at their 3'-ends giving rise to mRNAs containing (+) or lacking (-) the 3'-IRE (iron-responsive element) and resulting in altered C-terminal coding sequences. To determine whether these variations result in functional differences between isoforms, we explored the functional properties of each isoform using the voltage clamp and radiotracer assays in cRNA-injected Xenopus oocytes. 1A/IRE+-DMT1 mediated Fe2+-evoked currents that were saturable (K(0.5)(Fe) approximately 1-2 microM), temperature-dependent (Q10 approximately 2), H+-dependent (K(0.5)(H) approximately 1 muM) and voltage-dependent. 1A/IRE+-DMT1 exhibited the provisional substrate profile (ranked on currents) Cd2+, Co2+, Fe2+, Mn2+>Ni2+, V3+>>Pb2+. Zn2+ also evoked large currents; however, the zinc-evoked current was accounted for by H+ and Cl- conductances and was not associated with significant Zn2+ transport. 1B/IRE+-DMT1 exhibited the same substrate profile, Fe2+ affinity and dependence on the H+ electrochemical gradient. Each isoform mediated 55Fe2+ uptake and Fe2+-evoked currents at low extracellular pH. Whereas iron transport activity varied markedly between the four isoforms, the activity for each correlated with the density of anti-DMT1 immunostaining in the plasma membrane, and the turnover rate of the Fe2+ transport cycle did not differ between isoforms. Therefore all four isoforms of human DMT1 function as metal-ion transporters of equivalent efficiency. Our results reveal that the N- and C-terminal sequence variations among the DMT1 isoforms do not alter DMT1 functional properties. We therefore propose that these variations serve as tissue-specific signals or cues to direct DMT1 to the appropriate subcellular compartments (e.g. in erythroid cells) or the plasma membrane (e.g. in intestine).

Dataset Information

Two isoforms of a divalent metal transporter (DMT1) in Schistosoma mansoni suggest a surface-associated pathway for iron absorption in schistosomes.

Publications

Two isoforms of a divalent metal transporter (DMT1) in Schistosoma mansoni suggest a surface-associated pathway for iron absorption in schistosomes.

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