NifS-directed assembly of a transient [2Fe-2S] cluster within the NifU protein
NifS-directed assembly of a transient [2Fe-2S] cluster within the NifU protein
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DOI：
10.1073/pnas.97.2.599
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发表时间：
2000-01-18
影响因子：
11.1
通讯作者：
Dean, DR
中科院分区：
文献类型：
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作者：
Yuvaniyama, P;Agar, JN;Dean, DR
棕色固氮菌的NIF和NifU蛋白是完全激活固氮酶所必需的。NifS是一种同源二聚体半胱氨酸脱硫酶，为固氮酶组成蛋白中所含的Fe-S簇的形成提供所需的无机硫化物，NifU被认为可以通过动员固氮酶Fe-S簇形成所需的铁或通过提供一个中间的Fe-S簇组装位点来补充Nifs。分离到的同源二聚体NifU蛋白每个亚基含有一个[2Fe-2S](2+，+)簇，称为永久簇。在这份报告中，我们证明了NifU能够与Nifs相互作用，并且当铁离子、L-半胱氨酸和催化量的Nifs存在时，第二个瞬时的[2Fe-2S]簇可以在体外组装在NifU内。每个同二聚体大约组装了一个瞬时的[2Fe-2S]团簇，瞬时的[2Fe-2S]团簇物种是不稳定的，在还原时迅速释放。我们认为，瞬时的[2Fe-2S]簇单元在NifU上形成，然后释放，以提供固氮酶组成蛋白成熟所需的无机铁和硫。NifU中永久性的[2Fe-2S]团簇的作用尚不清楚，但它们可能具有氧化还原功能，涉及组装在NifU上的瞬时[2Fe-2S]团簇单元的形成或释放，因为在非固氮生物中发现了与NifU和Nifs的同源物，分别命名为IscU和Iscs，因此，本文提出的NifU的功能可能代表了含Fe-S簇状蛋白质成熟的一般机制。
The Nifs and NifU proteins from Azotobacter vinelandii are required for the full activation of nitrogenase. Nifs is a homodimeric cysteine desulfurase that supplies the inorganic sulfide necessary for formation of the Fe-S clusters contained with in the nitrogenase component proteins, NifU has been suggested to complement NifS either by mobilizing the Fe necessary for nitrogenase Fe-S cluster formation or by providing an intermediate Fe-S cluster assembly site. As isolated, the homodimeric NifU protein contains one [2Fe-2S](2+,+) cluster per subunit, which is referred to as the permanent cluster. In this report, we show that NifU is able to interact with Nifs and that a second, transient [2Fe-2S] cluster can be assembled within NifU in vitro when incubated in the presence of ferric ion, L-cysteine, and catalytic amounts of Nifs. Approximately one transient [2Fe-2S] cluster is assembled per homodimer, The transient [2Fe-2S] cluster species is labile and rapidly released on reduction. We propose that transient [2Fe-2S] cluster units are formed on NifU and then released to supply the inorganic iron and sulfur necessary for maturation of the nitrogenase component proteins. The role of the permanent [2Fe-2S] clusters contained within NifU is not yet known, but they could have a redox function involving either the formation or release of transient [2Fe-2S] cluster units assembled on NifU, Because homologs to both NifU and Nifs, respectively designated IscU and IscS, are found in non-nitrogen fixing organisms, it is possible that the function of NifU proposed here could represent a general mechanism for the maturation of Fe-s cluster-containing proteins.