Interaction with Cfd1 Increases the Kinetic Lability of FeS on the Nbp35 Scaffold

Abstract

P-loop NTPases of the ApbC/Nbp35 family are involved in FeS protein maturation in nearly all organisms and are proposed to function as scaffolds for initial FeS cluster assembly. In yeast and animals, Cfd1 and Nbp35 are homologous P-loop NTPases that form a heterotetrameric complex essential for FeS protein maturation through the cytosolic FeS cluster assembly (CIA) pathway. Cfd1 is conserved in animals, fungi, and several archaeal species, but in many organisms, only Nbp35 is present, raising the question of the unique roles played by Cfd1 and Nbp35. To begin to investigate this issue, we examined Cfd1 and Nbp35 function in budding yeast. About half of each protein was detected in a heterocomplex in logarithmically growing yeast. Nbp35 readily bound 55 Fe when fed to cells, whereas 55 Fe binding by free Cfd1 could not be detected. Rapid 55 Fe binding to and release from Nbp35 was impaired by Cfd1 deficiency. A Cfd1 mutation that caused a defect in heterocomplex stability supported iron binding to Nbp35 but impaired iron release. Our results suggest a model in which Cfd1-Nbp35 interaction increases the lability of assembled FeS on the Nbp35 scaffold for transfer to target apo-FeS proteins. Background: A Cfd1 and Nbp35 heterocomplex serves as scaffold for cytosolic iron-sulfur cluster assembly. Results: Deficiency in Cfd1-Nbp35 interaction impaired iron turnover on Nbp35. Conclusion: Cfd1 promotes binding and transfer of labile iron-sulfur cluster on the Nbp35 scaffold. Significance: This is the first insight into the unique roles of these P-loop ATPases in cytosolic iron-sulfur cluster assembly.