Function and crystal structure of the dimeric P-loop ATPase CFD1 coordinating an exposed [4Fe-4S] cluster for transfer to apoproteins

Significance Eukaryotic iron-sulfur (Fe-S) proteins play essential roles in energy conversion, antiviral defense, protein translation, genome integrity, and iron homeostasis. Assembly of the metallo-cofactors is assisted by complex machineries involving more than 30 known components. The initial phase of Fe-S protein maturation in the human cytosol is poorly studied thus far, with the P-loop nucleoside triphosphatase NBP35 being the only known assembly factor. Here, we identified and characterized human CFD1 as an indispensable complex partner of NBP35 in cytosolic Fe-S protein assembly (CIA). The crystal structure of fungal holo-Cfd1 showed a surface-exposed [4Fe-4S] cluster. Its shared, surface-exposed coordination by two Cfd1 monomers has important mechanistic implications for the ATP-dependent de novo cluster assembly and subsequent transfer to apoproteins via downstream CIA components.