Ojeda Luis, Keller Greg, Muhlenhoff Ulrich, Rutherford Julian C, Lill Roland, Winge Dennis R
Departments of Medicine and Biochemistry, University of Utah Health Sciences Center, Salt Lake City, UT 84132, USA.
J Biol Chem. 2006 Jun 30;281(26):17661-9. doi: 10.1074/jbc.M602165200. Epub 2006 Apr 28.
The transcription factors Aft1 and Aft2 from Saccharomyces cerevisiae regulate the expression of genes involved in iron homeostasis. These factors induce the expression of iron regulon genes in iron-deficient yeast but are inactivated in iron-replete cells. Iron inhibition of Aft1/Aft2 was previously shown to be dependent on mitochondrial components required for cytosolic iron sulfur protein biogenesis. We presently show that the nuclear monothiol glutaredoxins Grx3 and Grx4 are critical for iron inhibition of Aft1 in yeast cells. Cells lacking both glutaredoxins show constitutive expression of iron regulon genes. Overexpression of Grx4 attenuates wild type Aft1 activity. The thioredoxin-like domain in Grx3 and Grx4 is dispensable in mediating iron inhibition of Aft1 activity, whereas the conserved cysteine that is part of the conserved CGFS motif in monothiol glutaredoxins is essential for this function. Grx3 and Grx4 interact with Aft1 as shown by two-hybrid interactions and co-immunoprecipitation assays. The interaction between glutaredoxins and Aft1 is not modulated by the iron status of cells but is dependent on the conserved glutaredoxin domain Cys residue. Thus, Grx3 and Grx4 are novel components required for Aft1 iron regulation that most likely occurs in the nucleus.
酿酒酵母中的转录因子Aft1和Aft2调节参与铁稳态的基因表达。这些因子在缺铁酵母中诱导铁调节子基因的表达，但在铁充足的细胞中失活。先前已表明，Aft1/Aft2的铁抑制作用依赖于胞质铁硫蛋白生物合成所需的线粒体成分。我们目前表明，核单硫醇谷氧还蛋白Grx3和Grx4对酵母细胞中Aft1的铁抑制作用至关重要。缺乏这两种谷氧还蛋白的细胞显示出铁调节子基因的组成型表达。Grx4的过表达减弱了野生型Aft1的活性。Grx3和Grx4中类似硫氧还蛋白的结构域在介导Aft1活性的铁抑制作用中是可有可无的，而单硫醇谷氧还蛋白中保守的CGFS基序的一部分的保守半胱氨酸对于此功能至关重要。如双杂交相互作用和免疫共沉淀试验所示，Grx3和Grx4与Aft1相互作用。谷氧还蛋白与Aft1之间的相互作用不受细胞铁状态的调节，但依赖于保守的谷氧还蛋白结构域半胱氨酸残基。因此，Grx3和Grx4是Aft1铁调节所需的新成分，最有可能发生在细胞核中。
