The Human Iron鈥揝ulfur Assembly Complex Catalyzes the Synthesis of [2Fe-2S] Clusters on ISCU2 That Can Be Transferred to Acceptor Molecules

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• 作者：Nicholas G. Fox ; Mrinmoy Chakrabarti ; Sean P. McCormick ; Paul A. Lindahl ; David P. Barondeau
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：June 30, 2015
• 年：2015
• 卷：54
• 期：25
• 页码：3871-3879
• 全文大小：360K
• ISSN：1520-4995

文摘

Iron鈥搒ulfur (Fe鈥揝) clusters are essential protein cofactors for most life forms. In human mitochondria, the core Fe鈥揝 biosynthetic enzymatic complex (called SDUF) consists of NFS1, ISD11, ISCU2, and frataxin (FXN) protein components. Few mechanistic details about how this complex synthesizes Fe鈥揝 clusters and how these clusters are delivered to targets are known. Here circular dichroism and M枚ssbauer spectroscopies were used to reveal details of the Fe鈥揝 cluster assembly reaction on the SDUF complex. SDUF reactions generated [2Fe-2S] cluster intermediates that readily converted to stable [2Fe-2S] clusters bound to uncomplexed ISCU2. Similar reactions that included the apo Fe鈥揝 acceptor protein human ferredoxin (FDX1) resulted in formation of [2Fe-2S]-ISCU2 rather than [2Fe-2S]-FDX1. Subsequent addition of dithiothreitol (DTT) induced transfer of the cluster from ISCU2 to FDX1, suggesting that [2Fe-2S]-ISCU2 is an intermediate. Reactions that initially included DTT rapidly generated [2Fe-2S]-FDX1 and bypassed formation of [2Fe-2S]-ISCU2. In the absence of apo-FDX1, incubation of [2Fe-2S]-ISCU2 with DTT generated [4Fe-4S]-ISCU2 species. Together, these results conflict with a recent report of stable [4Fe-4S] cluster formation on the SDUF complex. Rather, they support a model in which SDUF builds transient [2Fe-2S] cluster intermediates that generate clusters on sulfur-containing molecules, including uncomplexed ISCU2. Additional small molecule or protein factors are required for the transfer of these clusters to Fe鈥揝 acceptor proteins or the synthesis of [4Fe-4S] clusters.