Chaperone Function in Iron-Sulfur Protein Folding

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DESCRIPTION: (Applicant's Description) Proteins containing iron-sulfur Clusters possess important electron transfer, catalytic, and regulatory functions, but the cellular mechanism by which Fe/S-clusters are formed and repaired is not known. Recently, a combination of biochemical and genetic studies have implicated several novel proteins in Fe/S-cluster biogenesis. In bacteria these proteins are encoded in a conserved gene cluster that includes three iron sulfur cluster assembly genes (IscS, lscU, IscA), two heat shock cognate chaperone genes (hscA and hscB), and a (2 Fe-2S)-ferredoxin (fdx). We have overexpressed arid purified each of the corresponding proteins from Escherichia Coli, and propose a combination of bioch mical and structural studies to investigate their roles in the assembly of Fe/S-clusters and the incorporation of Fe/S-clusters into proteins. The biochemical studies proposed will address 1) the mechanism of transfer of sulfide from the cysteine desulfurase lscS to the Fe/S-template protein lscU, 2) the role of IscA as a novel escort- metalllochaperone in providing iron for cluster assembly, 3) the interaction of lscU and its (2Fe-2S) complex with the Hsc66/H3c20 chaperone system, and 4) the transfer of Fe/S clusters to acceptor apo-proteins. X-ray crystallographic studies on the proteins are also proposed to provide structural insights into he molecular mechanisms involved. These studies should provide a better understanding of molecular mechanisms involved in the assembly of Fe/S clusters. Furthermore, it appears likely that a conserved mechanism of Fe/S-protein assembly occurs in eukaryotes, and the findings of these studies may provide new insights into the molecular basis of human diseases such as those associated with mitochondrial myopathies.