Mammalian Frataxin: An Essential Function for Cellular Viability through an Interaction with a Preformed ISCU/NFS1/ISD11 Iron-Sulfur Assembly Complex

BackgroundFrataxin, the mitochondrial protein deficient in Friedreich ataxia, a rare autosomal recessive neurodegenerative disorder, is thought to be involved in multiple iron-dependent mitochondrial pathways. In particular, frataxin plays an important role in the formation of iron-sulfur (Fe-S) clusters biogenesis.
Methodology/Principal FindingsWe present data providing new insights into the interactions of mammalian frataxin with the Fe-S assembly complex by combining in vitro and in vivo approaches. Through immunoprecipitation experiments, we show that the main endogenous interactors of a recombinant mature human frataxin are ISCU, NFS1 and ISD11, the components of the core Fe-S assembly complex. Furthemore, using a heterologous expression system, we demonstrate that mammalian frataxin interacts with the preformed core complex, rather than with the individual components. The quaternary complex can be isolated in a stable form and has a molecular mass of ≈190 kDa. Finally, we demonstrate that the mature human FXN81–210 form of frataxin is the essential functional form in vivo.
Conclusions/SignificanceOur results suggest that the interaction of frataxin with the core ISCU/NFS1/ISD11 complex most likely defines the essential function of frataxin. Our results provide new elements important for further understanding the early steps of de novo Fe-S cluster biosynthesis.

背景：frataxin（frataxin）是弗里德赖希共济失调（Friedreich ataxia）——一种罕见的常染色体隐性神经退行性疾病——中存在缺陷的线粒体蛋白，被认为参与多种铁依赖性线粒体通路。尤为关键的是，frataxin在铁硫（Fe-S）簇的生物发生过程中发挥重要作用。
方法与主要结果：本研究结合体外（in vitro）与体内（in vivo）实验手段，获取了关于哺乳动物frataxin与Fe-S组装复合物互作的全新见解。通过免疫沉淀实验，我们证实重组成熟型人源frataxin的主要内源性互作蛋白为ISCU、NFS1与ISD11——Fe-S组装核心复合物的组成组分。此外，借助异源表达系统，我们证明哺乳动物frataxin与预组装的核心复合物发生互作，而非与单个组分结合。该四元复合物可被稳定分离，其分子量约为190千道尔顿（kDa）。最后，我们证实成熟人源FXN81–210型frataxin是体内发挥功能的必需活性形式。
结论与意义：本研究结果表明，frataxin与ISCU/NFS1/ISD11核心复合物的互作，大概率决定了frataxin的核心生物学功能。本研究结果为进一步理解从头Fe-S簇生物合成的早期步骤提供了全新的关键依据。