Dix D R, Bridgham J T, Broderius M A, Byersdorfer C A, Eide D J
Department of Biochemistry and Molecular Biology, University of Minnesota, Duluth 55812.
J Biol Chem. 1994 Oct 21;269(42):26092-9.
Previous studies on Fe(II) uptake in Saccharomyces cerevisiae suggested the presence of two uptake systems with different affinities for this substrate. We demonstrate that the FET3 gene is required for high affinity uptake but not for the low affinity system. This requirement has enabled a characterization of the low affinity system. Low affinity uptake is time-, temperature-, and concentration-dependent and prefers Fe(II) over Fe(III) as substrate. We have isolated a new gene, FET4, that is required for low affinity uptake, and our results suggest that FET4 encodes an Fe(II) transporter protein. FET4's predicted amino acid sequence contains six potential transmembrane domains. Overexpressing FET4 increased low affinity uptake, whereas disrupting this gene eliminated that activity. In contrast, overexpressing FET4 decreased high affinity activity, while disrupting FET4 increased that activity. Therefore, the high affinity system may be regulated to compensate for alterations in low affinity activity. These analyses, and the analysis of the iron-dependent regulation of the plasma membrane Fe(III) reductase, demonstrate that the low affinity system is a biologically relevant mechanism of iron uptake in yeast. Furthermore, our results indicate that the high and low affinity systems are separate uptake pathways.
先前关于酿酒酵母中铁（II）摄取的研究表明，存在两种对该底物具有不同亲和力的摄取系统。我们证明FET3基因是高亲和力摄取所必需的，但对低亲和力系统则不是。这一需求使得对低亲和力系统的特性得以描述。低亲和力摄取是时间、温度和浓度依赖性的，并且比起铁（III）更喜欢铁（II）作为底物。我们分离出了一个新基因FET4，它是低亲和力摄取所必需的，并且我们的结果表明FET4编码一种铁（II）转运蛋白。FET4预测的氨基酸序列包含六个潜在的跨膜结构域。过表达FET4增加了低亲和力摄取，而破坏该基因则消除了该活性。相反，过表达FET4降低了高亲和力活性，而破坏FET4则增加了该活性。因此，高亲和力系统可能被调节以补偿低亲和力活性的改变。这些分析，以及对质膜铁（III）还原酶的铁依赖性调节的分析，表明低亲和力系统是酵母中铁摄取的一种生物学相关机制。此外，我们的结果表明高亲和力和低亲和力系统是独立的摄取途径。
