Si trova su / Altri legami
© 2021 American Chemical Society.IscU serves as a scaffold for the de novo assembly of a [2Fe–2S] cluster prior to its delivery to recipient protein. It has also been proposed that on one dimer of bacterial IscU, two [2Fe–2S] clusters can be converted into a single [4Fe–4S] cluster. However, lack of structural information about the dimeric state of IscU has hindered our understanding of the underlying mechanisms. In this study, we determine the X–ray crystal structure of IscU from the thermophilic archaeon Methanothrix thermoacetophila and demonstrate a dimer structure of IscU in which two [2Fe–2S] clusters are facing each other in close proximity at the dimer interface. Our structure also reveals for the first time that Asp40 serves as a fourth ligand to the [2Fe–2S] cluster with three Cys ligands in each monomer, consistent with previous spectroscopic data. We confirm by EPR spectroscopic analysis that in solution two adjacent [2Fe–2S] clusters in the wild–type dimer are converted to a [4Fe–4S] cluster via reductive coupling. Furthermore, we find that the H106A substitution abolishes the reductive conversion to the [4Fe–4S] cluster without structural alteration, suggesting that His106 is functionally involved in this process. Overall, these findings provide a structural explanation for the assembly and conversion of Fe–S clusters on IscU and highlight a dynamic process that advances via association and dissociation of the IscU dimer.
