Evidence for iron channeling in the Fet3p-Ftr1p high-affinity iron uptake complex in the yeast plasma membrane
Evidence for iron channeling in the Fet3p-Ftr1p high-affinity iron uptake complex in the yeast plasma membrane
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DOI：
10.1021/bi052173c
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发表时间：
2006-05-23
期刊：
影响因子：
2.9
通讯作者：
Kosman, Daniel J.
中科院分区：
文献类型：
--
作者：
Kwok, Ernest Y.;Severance, Scott;Kosman, Daniel J.
在酿酒酵母的高亲和力铁吸收中，Fe-II被多铜氧化酶Fet 3 p氧化为Fe-III，产生的Fe-III通过铁渗透酶Ftr 1 p转运到细胞中。这两种蛋白质可能是酵母质膜中异二聚体或更高级复合物的一部分。我们提供的动力学证据表明，Fet 3 p产生的Fe-III被贩运到Ftr 1 p的渗透由一个经典的代谢物通道机制。我们研究了Fe-59的吸收动力学的一些复合物含有突变形式的Fet 3 p和Ftr 1 p，并证明，一个蛋白质中的一个残基相互作用与一个在其他蛋白质沿着的铁运输途径，将预期在一个通道的过程。我们表明，由于这些突变，铁贩运变得敏感的Fe III螯合剂，抑制摄取在一个严格的竞争方式。这种抑制并不强烈依赖于螯合剂的强度，然而，这表明FeIII从铁吸收复合物的解离，如果它发生的话，是相对于铁渗透动力学缓慢。代谢物通道是多功能酶的共同特征。我们构建了类似的铁氧化酶，通透酶嵌合体，并证明它支持铁的吸收与通道机制的动力学模式一致。通过类比的Fe III贩运，导致矿化的铁蛋白核心，我们建议，三价铁通道是一个保守的功能，在好氧生物体中的铁稳态。
In high-affinity iron uptake in the yeast Saccharomyces cerevisiae, Fe-II is oxidized to Fe-III by the multicopper oxidase, Fet3p, and the Fe-III produced is transported into the cell via the iron permease, Ftr1p. These two proteins are likely part of a heterodimeric or higher order complex in the yeast plasma membrane. We provide kinetic evidence that the Fet3p-produced Fe-III is trafficked to Ftr1p for permeation by a classic metabolite channeling mechanism. We examine the Fe-59 uptake kinetics for a number of complexes containing mutant forms of both Fet3p and Ftr1p and demonstrate that a residue in one protein interacts with one in the other protein along the iron trafficking pathway as would be expected in a channeling process. We show that, as a result of some of these mutations, iron trafficking becomes sensitive to an added FeIII chelator that inhibits uptake in a strictly competitive manner. This inhibition is not strongly dependent on the chelator strength, however, suggesting that FeIII dissociation from the iron uptake complex, if it occurs, is kinetically slow relative to iron permeation. Metabolite channeling is a common feature of multifunctional enzymes. We constructed the analogous ferroxidase, permease chimera and demonstrate that it supports iron uptake with a kinetic pattern consistent with a channeling mechanism. By analogy to the FeIII trafficking that leads to the mineralization of the ferritin core, we propose that ferric iron channeling is a conserved feature of iron homeostasis in aerobic organisms.