The human YAE1-ORAOV1 complex of the cytosolic iron-sulfur protein assembly machinery binds a [4Fe-4S] cluster

Iron-sulfur (Fe-S) clusters are among the most versatile cofactors in biology. Although Fe-S clusters formation can be achieved spontaneously in vitro with inorganic iron and sulfur sources, the in vivo behaviour is more complex and requires the so-called Fe-S biogenesis machineries. In the cytosol, the biogenesis of Fe-S proteins is assisted by the cytosolic Fe-S protein assembly machinery, which comprises at least thirteen known proteins, among which there are human ORAOV1 and YAE1. A hetero-complex formed by the two latter proteins facilitates Fe-S cluster insertion in the human ABC protein ABCE1 within a chain of binding events that are still not well understood. In the present work, ORAOV1 and the YAE1-ORAOV1 complex were produced and their structural and cluster binding properties spectroscopically investigated. It resulted that both ORAOV1 and the YAE1-ORAOV1 complex are characterized by well-structured, α -helical regions and by unstructured, flexible regions, and are both able to bind a [4Fe-4S]2+ cluster. Bioinformatics and site-directed mutagenesis studies indicated that the [4Fe-4S] cluster in ORAOV1 is bound by a conserved cluster binding motif, while YAE1, which does not have a metal-binding consensus motif, is not essential for the [4Fe-4S]2+ cluster binding in the YAE1-ORAOV1 hetero-complex. Overall, these results support a model that the YAE1-ORAOV1 complex might actively participate in the Fe-S cluster insertion into ABCE1 thanks to the [4Fe-4S]2+ cluster binding properties of ORAOV1.