IscU as a scaffold for iron-sulfur cluster biosynthesis: Sequential assembly of [2Fe-2S] and [4Fe-4S] clusters in IscU
IscU as a scaffold for iron-sulfur cluster biosynthesis: Sequential assembly of [2Fe-2S] and [4Fe-4S] clusters in IscU
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DOI：
10.1021/bi000931n
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发表时间：
2000-07-11
期刊：
影响因子：
2.9
通讯作者：
Johnson, MK
中科院分区：
文献类型：
--
作者：
Agar, JN;Krebs, C;Johnson, MK
铁硫簇在原核和真核细胞中的生物合成是由两个高度保守的蛋白质介导的，在原核生物中称为IscS和IscU。同二聚体IscS蛋白已被证明是催化半胱氨酸还原转化为丙氨酸和硫化物的半胱氨酸脱硫酶。在这项工作中，通过无氧阴离子交换色谱法监测了IscU中IscS介导的Fe-S簇组装的时间过程，通过分析研究以及吸收、共振拉曼和穆斯堡尔研究评估了离散级分中组装的簇的性质和性质。结果表明，每个二聚体含有一个[2Fe-2S]（2+）簇的初始IscU产物首先转化为每个二聚体含有两个[2Fe-2S]（2+）簇的形式，最后转化为每个二聚体含有一个[4Fe-4S]（2+）簇的形式，IscU中的[2Fe-2S]（2+）和[4Fe-4S]（2+）团簇都是还原不稳定的，暴露于空气中几分钟内就会降解。基于序列分析和光谱研究，发现IscU中的[2Fe-2S]（2+）团簇具有不完全的半胱氨酰连接.此外，IscU中[4 Fe-4S]（2+）簇的共振拉曼光谱最好用独特Fe位点的非半胱氨酸连接来解释。在IscU中组装[2Fe-2S]（2+）和[4Fe-4S]（2+）簇的能力支持了这样的提议，即这种普遍存在的蛋白质为IscS介导的簇组装提供了支架，所述簇随后用于apo Fe-S蛋白的成熟。
Iron-sulfur cluster biosynthesis in both prokaryotic and eukaryotic cells is known to be mediated by two highly conserved proteins, termed IscS and IscU in prokaryotes. The homodimeric IscS protein has been shown to be a cysteine desulfurase that catalyzes the reductive conversion of cysteine to alanine and sulfide. In this work, the time course of IscS-mediated Fe-S cluster assembly in IscU was monitored via anaerobic anion exchange chromatography, The nature and properties of the clusters assembled in discrete fractions were assessed via analytical studies together with absorption, resonance Raman, and Mossbauer investigations. The results show sequential cluster assembly with the initial IscU product containing one [2Fe-2S](2+) cluster per dimer converting first to a form containing two [2Fe-2S](2+) clusters per dimer and finally to a form that contains one [4Fe-4S](2+) cluster per dimer, Both the [2Fe-2S](2+) and [4Fe-4S](2+) clusters in IscU are reductively labile and are degraded within minutes upon being exposed to air. On the basis of sequence considerations and spectroscopic studies, the [2Fe-2S](2+) clusters in IscU are shown to have incomplete cysteinyl ligation. In addition, the resonance Raman spectrum of the [4Fe-4S](2+) cluster in IscU is best interpreted in terms of noncysteinyl ligation at a unique Fe site. The ability to assemble both [2Fe-2S](2+) and [4Fe-4S](2+) clusters in IscU supports the proposal that this ubiquitous protein provides a scaffold for IscS-mediated assembly of clusters that are subsequently used for maturation of apo Fe-S proteins.