Formation and properties of [4Fe-4S] clusters on the IscU scaffold protein
Formation and properties of [4Fe-4S] clusters on the IscU scaffold protein
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DOI：
10.1021/bi6026659
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发表时间：
2007-06-12
期刊：
影响因子：
2.9
通讯作者：
Johnson, Michael K.
中科院分区：
文献类型：
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作者：
Chandramouli, Kala;Unciuleac, Mihaela-Carmen;Johnson, Michael K.
用紫外可见吸收光谱、穆斯堡尔谱和共振拉曼光谱，以二亚硫酸盐为电子供体，证明了两个[Fe-2-2S](2+)团簇在均二聚体Iscu Fe-S簇合物蛋白上快速定量地还原偶联形成一个[4Fe-4S](2+)团簇。用还原的Ise铁还蛋白也观察到了部分还原偶联，这增加了Ise铁还蛋白是生理还原剂的可能性。结果表明，ISCU上相邻的[2Fe-2S]~(2+)团簇的还原耦合为[4Fe-4S]~(21)团簇的生物合成提供了一种普遍的机制。Iscu上的[4Fe-4S](2+)中心可以还原为一个S=1/2[4Fe-4S](+)团簇(g(||)=2.06，g(垂直)=1.92)，但还原团簇的低中点势(-570 mV)和不稳定性与还原团簇的任何生理相关性相抵触。在O-2作用下，ISCU上的[4Fe-4S](2+)团簇通过半稳定的[2Fe-2S]2+团簇降解，其性质类似于[2Fe-2S](2+)ISCU上的[2Fe-2S](2+)中心。提示IscU能够适应细胞氧化还原状态和/或氧水平而调节[2Fe-2S](2+)或[4Fe-4S]2+簇的能力，可能为不同类型的[Fe-S]蛋白质的成熟提供了一种有效的途径。
Rapid and quantitative reductive coupling of two [Fe-2-2S](2+) clusters to form a single [4Fe-4S](2+) cluster on the homodimeric IscU Fe-S cluster scaffold protein has been demonstrated by UV-visible absorption, Mossbauer, and resonance Raman spectroscopies, using dithionite as the electron donor. Partial reductive coupling was also observed using reduced Ise ferredoxin, which raises the possibility that Ise ferredoxin is the physiological reductant. The results suggest that reductive coupling of adjacent [2Fe-2S]2+ clusters assembled on IscU provides a general mechanism for the final step in the biosynthesis of [4Fe-4S]21 clusters. The [4Fe-4S](2+) center on IscU can be reduced to a S = 1/2[4Fe-4S](+) cluster (g(||) = 2.06 and g(perpendicular to) = 1.92), but the low midpoint potential (< -570 mV) and instability of the reduced cluster argue against any physiological relevance for the reduced cluster. On exposure to O-2, the [4Fe-4S](2+) cluster on IscU degrades via a semistable [2Fe-2S]2+ cluster with properties analogous to those of the [2Fe-2S](2+) center in [2Fe-2S](2+) IscU. It is Suggested that the ability of IscU to accommodate either [2Fe-2S](2+) or [4Fe-4S]2+ clusters in response to cellular redox status and/or oxygen levels may provide an effective way to populate appropriately cluster-loaded forms of IscU for maturation of different types of [Fe-S] proteins.