Steinhilper Ralf, Boß Linda, Freibert Sven-A, Schulz Vinzent, Krapoth Nils, Kaltwasser Susann, Lill Roland, Murphy Bonnie J
Redox and Metalloprotein Research Group, Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438, Frankfurt am Main, Germany.
Institut für Zytobiologie, Philipps-Universität Marburg, Karl-von-Frisch-Str. 14, 35032, Marburg, Germany.
Nat Commun. 2024 Dec 4;15(1):10559. doi: 10.1038/s41467-024-54585-4.
Iron-sulfur (FeS) protein biogenesis in eukaryotes begins with the de novo assembly of [2Fe-2S] clusters by the mitochondrial core iron-sulfur cluster assembly (ISC) complex. This complex comprises the scaffold protein ISCU2, the cysteine desulfurase subcomplex NFS1-ISD11-ACP1, the allosteric activator frataxin (FXN) and the electron donor ferredoxin-2 (FDX2). The structural interaction of FDX2 with the complex remains unclear. Here, we present cryo-EM structures of the human FDX2-bound core ISC complex showing that FDX2 and FXN compete for overlapping binding sites. FDX2 binds in either a 'distal' conformation, where its helix F interacts electrostatically with an arginine patch of NFS1, or a 'proximal' conformation, where this interaction tightens and the FDX2-specific C terminus binds to NFS1, facilitating the movement of the [2Fe-2S] cluster of FDX2 closer to the ISCU2 FeS cluster assembly site for rapid electron transfer. Structure-based mutational studies verify the contact areas of FDX2 within the core ISC complex.
真核生物中铁硫（FeS）蛋白的生物合成始于线粒体核心铁硫簇组装（ISC）复合物从头组装[2Fe-2S]簇。该复合物由支架蛋白ISCU2、半胱氨酸脱硫酶亚复合物NFS1-ISD11-ACP1、变构激活剂共济失调蛋白（FXN）和电子供体铁氧化还原蛋白-2（FDX2）组成。FDX2与该复合物的结构相互作用仍不清楚。在这里，我们展示了结合人FDX2的核心ISC复合物的冷冻电镜结构，表明FDX2和FXN竞争重叠的结合位点。FDX2以“远端”构象结合，其螺旋F与NFS1的精氨酸区域发生静电相互作用，或以“近端”构象结合，这种相互作用增强，且FDX2特异性C末端与NFS1结合，促进FDX2的[2Fe-2S]簇向ISCU2 FeS簇组装位点移动，以实现快速电子转移。基于结构的突变研究验证了FDX2在核心ISC复合物中的接触区域。
