Frataxin binds iron

Frataxin (FXN) specifically binds 2 atoms of ferrous iron per monomer (reviewed in Stemmler et al. 2010). Iron bound to Frataxin may (Yoon and Cowan 2003, Gerber et al. 2003) or may not (Schmucker et al. 2011) enhance the interaction of Frataxin with NFS1, ICSU, and ISD11. Frataxin was shown to stimulate the cysteine desulfurase activity of NFS1 and was proposed to be a regulator of sulfur production (Tsai et al. 2010). The formation of sulfide by NFS1 is most efficiently observed when NFS1 is in complex with ISD11, ISCU, and FXN in the presence of cysteine and iron. This means that only the complete system of NFS1, ISD11, ISCU, FXN, cysteine, and iron is fully active as a desulfurase. FXN therefore seems to be a regulator of the cysteine desulfurase permitting sulfide production only when all components needed for Fe-S cluster synthesis are present and the ISCU-bound Fe-S cluster can be formed.

富铁蛋白（FXN）与每个单体特异性结合两个铁原子（参见 Stemmler 等人，2010 年综述）。与富铁蛋白结合的铁可能（Yoon 和 Cowan，2003 年；Gerber 等人，2003 年）或可能不会（Schmucker 等人，2011 年）增强富铁蛋白与 NFS1、ICSU 和 ISD11 的相互作用。研究表明，富铁蛋白可刺激 NFS1 的半胱氨酸脱硫酶活性，并被提出作为硫生产调节因子（Tsai 等人，2010 年）。当 NFS1 与 ISD11、ISCU 和 FXN 复合存在，并在半胱氨酸和铁的存在下，硫化物的形成最为有效。这意味着，只有 NFS1、ISD11、ISCU、FXN、半胱氨酸和铁的完整系统才能作为脱硫酶完全活跃。因此，FXN 似乎充当半胱氨酸脱硫酶的调节因子，仅当所有合成 Fe-S 簇所需的成分均存在，且 ISCU 结合的 Fe-S 簇能够形成时，才允许硫化物的产生。