Multimodal Spectroscopic Analysis of the Fe–S Clusters of the as-Isolated Escherichia coli SufBC2D Complex

Iron–sulfur (Fe–S) clusters are essential inorganic cofactors dedicated to a wide range of biological functions, including electron transfer and catalysis. Specialized multiprotein machineries present in all types of organisms support their biosynthesis. These machineries encompass a scaffold protein, on which Fe–S clusters are assembled before being transferred to cellular targets. Here, we describe the first characterization of the native Fe–S cluster of the anaerobically purified SufBC2D scaffold from Escherichia coli by XAS and Mössbauer, UV–visible absorption, and EPR spectroscopies. Interestingly, we propose that SufBC2D harbors two iron–sulfur-containing species, a [2Fe-2S] cluster and an as-yet unidentified species. Mutagenesis and biochemistry were used to propose amino acid ligands for the [2Fe-2S] cluster, supporting the hypothesis that both SufB and SufD are involved in the Fe–S cluster ligation. The [2Fe-2S] cluster can be transferred to ferredoxin in agreement with the SufBC2D scaffold function. These results are discussed in the context of Fe–S cluster biogenesis.