Coordinate Regulation of the Suf and Isc Fe-S Cluster Biogenesis Pathways by IscR Is Essential for Viability of Escherichia coli

Abstract

Fe-S cluster biogenesis is essential for the viability of most organisms. In Escherichia coli, this process requires either the housekeeping Isc or the stress-induced Suf pathway. The global regulator IscR coordinates cluster synthesis by repressing transcription of the isc operon by [2Fe-2S]-IscR and activating expression of the suf operon. We show that either [2Fe-2S]-IscR or apoIscR can activate suf, making expression sensitive to mainly IscR levels and not the cluster state, unlike isc expression. We also demonstrate that in the absence of isc, IscR-dependent suf activation is essential since strains lacking both the Isc pathway and IscR were not viable unless Suf was expressed ectopically. Similarly, removal of the IscR binding site in the sufA promoter also led to a requirement for isc. Furthermore, suf expression was increased in a ⌬isc mutant, presumably due to increased IscR levels in this mutant. This was surprising because the iron-dependent repressor Fur, whose higher-affinity binding at the sufA promoter should occlude IscR binding, showed only partial repression. In addition, Fur derepression was not sufficient for viability in the absence of IscR and the Isc pathway, highlighting the importance of direct IscR activation. Finally, a mutant lacking Fur and the Isc pathway increased suf expression to the highest observed levels and nearly restored [2Fe-2S]-IscR activity, providing a mechanism for regulating IscR activity under stress conditions. Together, these findings have enhanced our understanding of the homeostatic mechanism by which cells use one regulator, IscR, to differentially control Fe-S cluster biogenesis pathways to ensure viability.

The EcoCyc database: reflecting new knowledge aboutEscherichia coliK-12

“…IscR-[2Fe-2S] negatively regulates the expression of iscRSUA , genes of the Isc Fe–S cluster biosynthesis pathway, and activates expression of the sufABCDSE operon, which encodes the Suf Fe-S cluster biosynthesis pathway. Coordinated regulation of these two pathways maintains differential control of Fe–S cluster biogenesis and ensures viability under a variety of growth conditions (14). Both apo-IscR and the IscR-[2Fe–2S] holoprotein conformations were able to activate the Suf pathway (14).…”

“…Coordinated regulation of these two pathways maintains differential control of Fe–S cluster biogenesis and ensures viability under a variety of growth conditions (14). Both apo-IscR and the IscR-[2Fe–2S] holoprotein conformations were able to activate the Suf pathway (14). …”

Protective role of bacillithiol in superoxide stress and Fe–S metabolism inBacillus subtilis

“…Bacillus subtilis lacks the Fe–S transcriptional regulator IscR (Giel et al. ; Mettert and Kiley ) and preliminary results described here suggest that this pathway may be subjected to distinct yet‐unidentified mechanism(s).…”

Elevated Expression of a Functional Suf Pathway in theE.coliBL21(DE3) Cell Line Enhances Recombinant Production of an Iron-Sulfur Cluster Containing Protein

“…1c). Activity of this mutant fusion protein was tested using P1 vir to transduce into BL21(DE3) a ∆ iscSUAhscBAfdx::kan allele which requires a functional Suf pathway for growth (14). No BL21(DE3) derivatives were recovered, suggesting that this fusion protein, and consequently, the Suf pathway, is non-functional in this strain.…”