Iron-Sulfur (Fe-S) Cluster Assembly

Abstract

Assembly of iron-sulfur (Fe-S) clusters and maturation of Fe-S proteins in vivo require complex machineries. In Escherichia coli, under adverse stress conditions, this process is achieved by the SUF system that contains six proteins as follows: SufA, SufB, SufC, SufD, SufS, and SufE. Here, we provide a detailed characterization of the SufBCD complex whose function was so far unknown. Using biochemical and spectroscopic analyses, we demonstrate the following: (i) the complex as isolated exists mainly in a 1:2:1 (B:C:D) stoichiometry; (ii) the complex can assemble a [4Fe-4S] cluster in vitro and transfer it to target proteins; and (iii) the complex binds one molecule of flavin adenine nucleotide per SufBC2D complex, only in its reduced form (FADH2), which has the ability to reduce ferric iron. These results suggest that the SufBC2D complex functions as a novel type of scaffold protein that assembles an Fe-S cluster through the mobilization of sulfur from the SufSE cysteine desulfurase and the FADH2-dependent reductive mobilization of iron. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.