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Molecular impact of divalent metal-ion transporter (DMT1) mutations (V114del and G212V) found in a compound heterozygote with microcytic anemia and hepatic iron overload

Department of Molecular & Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, OH

ABSTRACT

DMT1 is a H⁺-coupled divalent metal-ion transporter critical for intestinal iron (Fe) absorption and erythroid Fe utilization. Beaumont et al (Blood 107, 4168 [2006]) described a patient compound heterozygous for two new DMT1 mutations (V114 deletion and G212V) associated with hypochromic-microcytic anemia and hepatic Fe overload. The proband’s sibling and parents each possess one mutated allele but were asymptomatic. We expressed mutant and wildtype (wt) DMT1 in Xenopus oocytes and used voltage-clamp and radiotracer assays to examine the molecular impact of these novel mutations. The V114 deletion abolished ⁵⁵Fe²⁺ transport activity whereas ⁵⁵Fe²⁺ transport mediated by G212V-DMT1 did not differ from wtDMT1. G212V had no effect on the pH dependence of ⁵⁵Fe²⁺ transport, presteady-state kinetics, or the affinity for Fe²⁺ (K_0.5 = 1.7 ± 1.1 µM c.f. 1.3 ± 0.5 µM in wtDMT1). To our surprise, however, G212V-DMT1 mediated much smaller Fe²⁺-evoked currents than did wtDMT1. From simultaneous measurement of currents and ⁵⁵Fe²⁺ fluxes, we arrived at a wildtype H⁺/Fe²⁺ ratio of 17 ± 1 which greatly exceeds that expected for strict stoichiometric transport, i.e. most of the wtDMT1-mediated current arises from H⁺ slippage. Such slippage is normally thought of in terms of the energetic penalty to the cell; however, indications that H⁺ slippage, but not Fe²⁺ transport, is disrupted in the G212V mutant associated with disease raise the possibility that H⁺ slippage serve a physiological role.

This Article Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Shawki, A. Articles by Mackenzie, B. PubMed Articles by Shawki, A. Articles by Mackenzie, B.