NDLI: Functional properties of multiple isoforms of human divalent metal-ion transporter 1 (DMT1)

Content Provider	PubMed Central
Author	Mackenzie, Bryan Takanaga, Hitomi Hubert, Nadia Rolfs, Andreas Hediger, Matthias A.
Copyright Year	2007
Abstract	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≈1–2 μM), temperature-dependent (Q 10≈2), H+-dependent (K 0.5 H≈1 μM) 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).
Related Links	http://dx.doi.org/10.1042/bj20061290
Ending Page	69
Page Count	11
Starting Page	59
File Format	PDF
ISSN	02646021
e-ISSN	14708728
Journal	Biochemical Journal
Issue Number	Pt 1
Volume Number	403
Language	English
Publisher	Portland Press Ltd.
Publisher Date	2007-04-01
Access Restriction	Open
Rights Holder	Portland Press Ltd.
Subject Keyword	Cell Biology Biochemistry Molecular Biology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Cell Biology Molecular Biology Biochemistry

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