Frataxin (FXN) is involved in mitochondrial iron‑sulfur (Fe-S) cluster biogenesis and serves to accelerate Fe-S cluster formation. FXN deficiency is associated with Friedreich ataxia, a neurodegenerative disease. We have used a combination of isothermal titration calorimetry and multinuclear NMR spectroscopy to investigate interactions among the components of the biological machine that carries out the assembly of iron‑sulfur clusters in human mitochondria. Our results show that FXN tightly binds a single Fe²⁺ but not Fe³⁺. While FXN (with or without bound Fe²⁺) does not bind the scaffold protein ISCU directly, the two proteins interact mutually when each is bound to the cysteine desulfurase complex ([NFS1]₂:[ISD11]₂:[Acp]₂), abbreviated as (NIA)₂, where “N” represents the cysteine desulfurase (NFS1), “I” represents the accessory protein (ISD11), and “A” represents acyl carrier protein (Acp). FXN binds (NIA)₂ weakly in the absence of ISCU but more strongly in its presence. Fe²⁺-FXN binds to the (NIA)₂-ISCU₂ complex without release of iron. However, upon the addition of both l-cysteine and a reductant (either reduced FDX2 or DTT), Fe²⁺ is released from FXN as consistent with Fe²⁺-FXN being the proximal source of iron for Fe-S cluster assembly.

Frataxin (FXN) 参与线粒体铁硫 (Fe-S) 簇的生物合成，并有助于加速 Fe-S 簇的形成。FXN 缺乏与弗里德赖希共济失调（一种神经退行性疾病）有关。我们结合使用等温滴定量热法和多核核磁共振波谱来研究在人类线粒体中组装铁硫簇的生物机器组件之间的相互作用。我们的结果表明，FXN 紧密结合单个 Fe ²⁺而不是 Fe ³⁺。虽然 FXN（结合或不结合 Fe ²⁺）不直接结合支架蛋白 ISCU，但当两种蛋白各自结合半胱氨酸脱硫酶复合物时，它们会相互作用 ([NFS1] ₂ :[ISD11] ₂ :[Acp] ₂ ) ，缩写为(NIA) ₂，其中“N”代表半胱氨酸脱硫酶(NFS1)，“I”代表辅助蛋白(ISD11)，“A”代表酰基载体蛋白(Acp)。在 ISCU 不存在的情况下， FXN 与 (NIA) _{2 的}结合较弱，但在 ISCU 存在的情况下，FXN 与 (NIA) 2 的结合较强。Fe ²⁺ -FXN 与 (NIA) ₂ -ISCU ₂复合物结合而不释放铁。然而，在添加l-半胱氨酸和还原剂（还原的FDX2或DTT）后，Fe ²⁺从FXN中释放，这与Fe ²⁺ -FXN是Fe-S簇组装的近铁源一致。