Divalent metal-ion transporter DMT1 mediates both H+-coupled Fe2+ transport and uncoupled fluxes
Divalent metal-ion transporter DMT1 mediates both H+-coupled Fe2+ transport and uncoupled fluxes
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DOI：
10.1007/s00424-005-1494-3
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发表时间：
2006-01-01
影响因子：
4.5
通讯作者：
Hediger, MA
中科院分区：
文献类型：
--
作者：
Mackenzie, B;Ujwal, ML;Hediger, MA
H+ 偶联的二价金属离子转运蛋白 DMT1 既是铁进入体内的主要入口点（肠道刷状缘摄取），也是转铁蛋白相关铁从内体动员到红系前体细胞和其他细胞的细胞质的途径。因此，阐明 DMT1 的分子机制将增加我们对铁代谢和铁过载疾病病因学的理解。我们在非洲爪蟾卵母细胞中表达野生型和突变型 DMT1，并监测金属离子摄取、电流和细胞内 pH 值。 DMT1 在存在向内的 H+ 电化学梯度的情况下被激活。在低细胞外 pH (pH(o)) 下，H+ 结合先于 Fe2+ 结合及其同时易位。然而，DMT1 在较高 pH(o) 下的行为并不像典型的离子耦合转运蛋白，并且在 pH(o) 7.4 时，我们观察到与 H+ 流入无关的 Fe2+ 转运。 His(272) --> Ala 取代使 Fe2+ 和 H+ 通量解耦。在低 pH(o) 下，H272A 介导的 H+ 单向端口被 Fe2+ 抑制。同时H272A介导的Fe2+转运与pH(o)无关。我们的数据表明（i）DMT1 中的 H+ 偶联可增加对 Fe2+ 的亲和力，并为 Fe2+ 运输提供热力学驱动力；（ii）His-272 在转换 H+ 偶联效应中至关重要。值得注意的是，我们的数据还表明，在没有 H+ 梯度的情况下，DMT1 可以介导促进 Fe2+ 转运。由于 DMT1 的质膜表达在血色素沉着病患者的肝脏中上调，这种通过 DMT1 的 H+ 解偶联促进 Fe2+ 转运可以解释铁过载疾病特征的非转铁蛋白结合血浆铁的摄取。
The H+-coupled divalent metal-ion transporter DMT1 serves as both the primary entry point for iron into the body ( intestinal brush-border uptake) and the route by which transferrin-associated iron is mobilized from endosomes to cytosol in erythroid precursors and other cells. Elucidating the molecular mechanisms of DMT1 will therefore increase our understanding of iron metabolism and the etiology of iron overload disorders. We expressed wild type and mutant DMT1 in Xenopus oocytes and monitored metal-ion uptake, currents and intracellular pH. DMT1 was activated in the presence of an inwardly directed H+ electrochemical gradient. At low extracellular pH (pH(o)), H+ binding preceded binding of Fe2+ and its simultaneous translocation. However, DMT1 did not behave like a typical ion-coupled transporter at higher pH(o), and at pH(o) 7.4 we observed Fe2+ transport that was not associated with H+ influx. His(272) --> Ala substitution uncoupled the Fe2+ and H+ fluxes. At low pH(o), H272A mediated H+ uniport that was inhibited by Fe2+. Meanwhile H272A-mediated Fe2+ transport was independent of pH(o). Our data indicate (i) that H+ coupling in DMT1 serves to increase affinity for Fe2+ and provide a thermodynamic driving force for Fe2+ transport and (ii) that His-272 is critical in transducing the effects of H+ coupling. Notably, our data also indicate that DMT1 can mediate facilitative Fe2+ transport in the absence of a H+ gradient. Since plasma membrane expression of DMT1 is upregulated in liver of hemochromatosis patients, this H+ -uncoupled facilitative Fe2+ transport via DMT1 can account for the uptake of nontransferrin-bound plasma iron characteristic of iron overload disorders.