Novel features of the ISC machinery revealed by characterization of Escherichia coli mutants that survive without iron–sulfur clusters

Abstract

Biological assembly of iron-sulfur (Fe-S) clusters is mediated by complex systems consisting of multiple proteins. Escherichia coli possesses two distinct systems called the ISC and SUF machineries encoded by iscSUA-hscBA-fdx-iscX and sufABCDSE respectively. Deletion of both pathways results in absence of the biosynthetic apparatus for Fe-S clusters, and consequent lethality, which has hampered detailed genetic studies. Here we report that modification of the isoprenoid biosynthetic pathway can offset the indispensability of the Fe-S cluster biosynthetic systems and show that the resulting Δisc Δsuf double mutants can grow without detectable Fe-S cluster-containing proteins. We also constructed a series of mutants in which each isc gene was disrupted in the deletion background of sufABCDSE. Phenotypic analysis of the mutants revealed that Fdx, an essential electron-transfer Fe-S protein in the ISC machinery, is dispensable under anaerobic conditions, which is similar to the situation with IscA. Furthermore, we found that several suppressor mutations in IscU, an Fe-S scaffold protein responsible for the de novo Fe-S cluster assembly, could bypass the essential role of the chaperone system HscA and HscB. These findings pave the way toward a detailed molecular analysis to understand the mechanisms involved in Fe-S cluster biosynthesis.

The RicAFT (YmcA‐YlbF‐YaaT) complex carries two [4Fe‐4S]2+ clusters and may respond to redox changes

“…Yet another attractive possibility is that the complex serves a role in [Fe‐S] cluster assembly on apo‐proteins. Consistent with this idea is the observation that ricA, ricF and ricT mutants exhibit marked growth defects in minimal medium but not in complex media, which would be expected if [Fe‐S] cluster biogenesis or assembly are impaired, since many biosynthetic reactions are mediated by [Fe‐S] enzymes (Schwartz et al ., ; Albrecht et al ., ; Tanaka et al ., ).…”

Engineering a functional 1-deoxy-D-xylulose 5-phosphate (DXP) pathway in Saccharomyces cerevisiae

“…Since IspG and IspH are both [4Fe-4S] enzymes, a natural starting point is to investigate whether the problem is predominantly a limitation in iron-sulfur cluster assembly. The importance of [4Fe-4S] cluster biosynthesis for these two enzymes was underlined by the recent demonstration that E. coli can survive a knockout of both Fe-S assembly systems, ISC and SUF, as long as mevalonate and the lower genes of the mevalonate pathway are provided to ensure a supply of IPP and DMAPP (Tanaka et al, 2016). It’s also interesting to note that while pathogenic strains of Listeria monocytogenes maintain a full DXP pathway as well as a mevalonate pathway, its non-pathogenic relative Listeria innocua has specifically lost the genes encoding IspG and IspH, suggesting that these two [4Fe-4S] enzymes may constitute a high metabolic or physiological burden (Begley et al, 2008).…”

A Sinorhizobium meliloti RpoH-Regulated Gene Is Involved in Iron-Sulfur Protein Metabolism and Effective Plant Symbiosis under Intrinsic Iron Limitation

“…Thus, our data suggest that SufT serves for the maintenance of various Fe/S proteins, although [2Fe-2S] cluster-containing proteins remain to be examined in this respect. An increase in malate dehydrogenase activity might be a general symptom of metabolic perturbation caused by Fe/S protein defects; indeed, this activity is markedly increased in E. coli mutants unable to build Fe/S clusters (27).…”

“…These proteins thus serve for de novo assembly of Fe/S clusters. SufA is an A-type carrier suggested to have a [4Fe-4S] cluster-specific function (26,27). In S. meliloti, homologs of those SUF components are encoded by the gene cluster sufBCDS-SMc00302-sufA (Fig.…”