The cysteine desulfurase, IscS, has a major role in in vivo Fe-S cluster formation in Escherichia coli

Abstract

The cysteine desulfurase, IscS, provides sulfur for Fe-S cluster synthesis in vitro, but a role for IscS in in vivo Fe-S cluster formation has yet to be established. To study the in vivo function of IscS in Escherichia coli, a strain lacking IscS was constructed and characterized. Using this iscS deletion strain, we have observed decreased specific activities for proteins containing [4Fe-4S] clusters from soluble (aconitase B, 6-phosphogluconate dehydratase, glutamate synthase, fumarase A, and FNR) and membrane-bound proteins (NADH dehydrogenase I and succinate dehydrogenase). A specific role for IscS in in vivo Fe-S cluster assembly was demonstrated by showing that an Fe-S cluster independent mutant of FNR is unaffected by the lack of IscS. These data support the conclusion that, via its cysteine desulfurase activity, IscS provides the sulfur that subsequently becomes incorporated during in vivo Fe-S cluster synthesis. We also have characterized a growth phenotype associated with the loss of IscS. Under aerobic conditions the deletion of IscS caused an auxotrophy for thiamine and nicotinic acid, whereas under anaerobic conditions, only nicotinic acid was required. The lack of IscS also had a general effect on the growth of E. coli because the iscS deletion strain grew at half the rate of wild type in many types of media even when the auxotrophies were satisfied.NifS ͉ FNR ͉ oxidative stress repair ͉ sulfur metabolism

The O 2 sensitivity of the transcription factor FNR is controlled by Ser24 modulating the kinetics of [4Fe-4S] to [2Fe-2S] conversion

“…Our current understanding is that FNR is continually supplied with [4Fe-4S] 2ϩ clusters by the iron-sulfur cluster biosynthetic machinery (25)(26)(27), but O 2 converts the [4Fe-4S] 2ϩ cluster to a [3Fe-4S] ϩ cluster that spontaneously disassembles to yield a [2Fe-2S] 2ϩ cluster with concomitant inactivation of FNR (12,15,22,23). The properties of FNR-S24F described here are entirely consistent with this view of the FNR switch.…”

The SufE Protein and the SufBCD Complex Enhance SufS Cysteine Desulfurase Activity as Part of a Sulfur Transfer Pathway for Fe-S Cluster Assembly in Escherichia coli

“…In some organisms, the hscB-hscA-fdx operon is co-expressed with isc but in E. coli the two operons are regulated separately (3,19,20). In vivo the isc operon together with the hscB-hscA-fdx genes have been shown to be important for the assembly of a variety of Fe-S enzymes (18,21). The second E. coli NifS homologue, CsdA, is encoded adjacent to the ygdK gene, which encodes a homologue of SufE.…”

AtNAP7 is a plastidic SufC-like ATP-binding cassette/ATPase essential for Arabidopsis embryogenesis

“…The NIF system is most specific, involved in the assembly and maturation of Fe-S clusters in nitrogenase proteins (7) in nitrogen-fixing bacteria and -proteobacteria (8), whereas the ISC system is more general and is found in both bacteria and higher eukaryotes (9)(10)(11)(12)(13). Although classified as two distinct systems, similarities exist between the two in that the N-terminal domain of NifU corresponds to IscU (14)(15)(16), and NifS shows functional similarity to IscS (9).…”