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Ferric uptake regulator (Fur) reversibly binds a [2Fe-2S] cluster to sense intracellular iron homeostasis in Escherichia coli.
Journal of Biological Chemistry ( IF 5.5 ) Pub Date : 2020-11-13 , DOI: 10.1074/jbc.ra120.014814
Chelsey R Fontenot 1 , Homyra Tasnim 1 , Kathryn A Valdes 2 , Codrina V Popescu 2 , Huangen Ding 1
Affiliation  

The ferric uptake regulator (Fur) is a global transcription factor that regulates intracellular iron homeostasis in bacteria. The current hypothesis states that when the intracellular “free” iron concentration is elevated, Fur binds ferrous iron, and the iron-bound Fur represses the genes encoding for iron uptake systems and stimulates the genes encoding for iron storage proteins. However, the “iron-bound” Fur has never been isolated from any bacteria. Here we report that the Escherichia coli Fur has a bright red color when expressed in E. coli mutant cells containing an elevated intracellular free iron content because of deletion of the iron–sulfur cluster assembly proteins IscA and SufA. The acid-labile iron and sulfide content analyses in conjunction with the EPR and Mössbauer spectroscopy measurements and the site-directed mutagenesis studies show that the red Fur protein binds a [2Fe-2S] cluster via conserved cysteine residues. The occupancy of the [2Fe-2S] cluster in Fur protein is ∼31% in the E. coli iscA/sufA mutant cells and is decreased to ∼4% in WT E. coli cells. Depletion of the intracellular free iron content using the membrane-permeable iron chelator 2,2´-dipyridyl effectively removes the [2Fe-2S] cluster from Fur in E. coli cells, suggesting that Fur senses the intracellular free iron content via reversible binding of a [2Fe-2S] cluster. The binding of the [2Fe-2S] cluster in Fur appears to be highly conserved, because the Fur homolog from Hemophilus influenzae expressed in E. coli cells also reversibly binds a [2Fe-2S] cluster to sense intracellular iron homeostasis.

中文翻译:

铁摄取调节剂(Fur)可逆地结合[2Fe-2S]簇,以感应大肠杆菌中的细胞内铁稳态。

铁摄取调节剂(Fur)是调节细菌中细胞内铁稳态的全局转录因子。当前的假设表明,当细胞内“游离”铁浓度升高时,Fur结合亚铁,并且与铁结合的Fur抑制编码铁吸收系统的基因,并刺激编码铁存储蛋白的基因。但是,从未从任何细菌中分离出“铁结合的”毛皮。在这里我们报告说,由于在铁-硫簇装配蛋白IscA和SufA的缺失下,含有较高的细胞内游离铁含量的大肠杆菌突变细胞中表达时,大肠杆菌毛发呈亮红色。酸不稳定的铁和硫化物含量分析以及EPR和Mössbauer光谱测量以及定点诱变研究表明,红色的Fur蛋白通过保守的半胱氨酸残基结合[2Fe-2S]簇。在大肠杆菌iscA / sufA突变细胞中,Fur蛋白中[2Fe-2S]簇的占有率为〜31%,而在野生型大肠杆菌细胞中,占有率为[4Fe-2S]簇,下降为〜4%。使用膜透性铁螯合剂2,2′-联吡啶消除细胞内游离铁含量,可有效去除大肠杆菌细胞中Fur的[2Fe-2S]簇,这表明Fur通过可逆结合作用感知细胞内游离铁含量。 [2Fe-2S]簇。[2Fe-2S]簇在Fur中的结合看来是高度保守的,因为来自流感嗜血杆菌的Fur同源物在大肠杆菌中表达。
更新日期:2020-11-13
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