Dataset Information

Iron-sulfur cluster assembly scaffold protein IscU is required for activation of ferric uptake regulator (Fur) in Escherichiacoli.

ABSTRACT: It was generally postulated that when intracellular free iron content is elevated in bacteria, the ferric uptake regulator (Fur) binds its corepressor a mononuclear ferrous iron to regulate intracellular iron homeostasis. However, the proposed iron-bound Fur had not been identified in any bacteria. In previous studies, we have demonstrated that Escherichia coli Fur binds a [2Fe-2S] cluster in response to elevation of intracellular free iron content and that binding of the [2Fe-2S] cluster turns on Fur as an active repressor to bind a specific DNA sequence known as the Fur-box. Here we find that the iron-sulfur cluster assembly scaffold protein IscU is required for the [2Fe-2S] cluster assembly in Fur, as deletion of IscU inhibits the [2Fe-2S] cluster assembly in Fur and prevents activation of Fur as a repressor in E. coli cells in response to elevation of intracellular free iron content. Additional studies reveal that IscU promotes the [2Fe-2S] cluster assembly in apo-form Fur and restores its Fur-box binding activity in vitro. While IscU is also required for the [2Fe-2S] cluster assembly in the Haemophilus influenzae Fur in E. coli cells, deletion of IscU does not significantly affect the [2Fe-2S] cluster assembly in the E. coli ferredoxin and siderophore-reductase FhuF. Our results suggest that IscU may have a unique role for the [2Fe-2S] cluster assembly in Fur and that regulation of intracellular iron homeostasis is closely coupled with iron-sulfur cluster biogenesis in E. coli.

SUBMITTER: Purcell AG

PROVIDER: S-EPMC11001641 | biostudies-literature | 2024 Mar

REPOSITORIES: biostudies-literature

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Iron-sulfur cluster assembly scaffold protein IscU is required for activation of ferric uptake regulator (Fur) in Escherichiacoli.

Purcell Aidan G AG Fontenot Chelsey R CR Ding Huangen H

The Journal of biological chemistry 20240305 4

It was generally postulated that when intracellular free iron content is elevated in bacteria, the ferric uptake regulator (Fur) binds its corepressor a mononuclear ferrous iron to regulate intracellular iron homeostasis. However, the proposed iron-bound Fur had not been identified in any bacteria. In previous studies, we have demonstrated that Escherichia coli Fur binds a [2Fe-2S] cluster in response to elevation of intracellular free iron content and that binding of the [2Fe-2S] cluster turns ...[more]

PMID: 38452854

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Project description:UnlabelledClostridium difficile is an anaerobic, Gram-positive, spore-forming opportunistic pathogen and is the most common cause of hospital-acquired infectious diarrhea. Although iron acquisition in the host is a key to survival of bacterial pathogens, high levels of intracellular iron can increase oxidative damage. Therefore, expression of iron acquisition mechanisms is tightly controlled by transcriptional regulators. We identified a C. difficile homologue of the master bacterial iron regulator Fur. Using targetron mutagenesis, we generated a fur insertion mutant of C. difficile. To identify the genes regulated by Fur in C. difficile, we used microarray analysis to compare transcriptional differences between the fur mutant and the wild type when grown in high-iron medium. The fur mutant had increased expression of greater than 70 transcriptional units. Using quantitative reverse transcriptase PCR (qRT-PCR), we analyzed several of the Fur-regulated genes identified by the microarray and verified that they are both iron and Fur regulated in C. difficile. Among those Fur- and iron-repressed genes were C. difficile genes encoding 7 putative cation transport systems of different classes. We found that Fur was able to bind the DNA upstream of three Fur-repressed genes in electrophoretic mobility shift assays. We also demonstrate that expression of Fur-regulated putative iron acquisition systems was increased during C. difficile infection using the hamster model. Our data suggest that C. difficile expresses multiple iron transport mechanisms in response iron depletion in vitro and in vivo.ImportanceClostridium difficile is the most common cause of hospital-acquired infectious diarrhea and has been recently classified as an "urgent" antibiotic resistance threat by the CDC. To survive and cause disease, most bacterial pathogens must acquire the essential enzymatic cofactor iron. While import of adequate iron is essential for most bacterial growth, excess intracellular iron can lead to extensive oxidative damage. Thus, bacteria must regulate iron import to maintain iron homeostasis. We demonstrate here that C. difficile regulates expression of several putative iron acquisition systems using the transcriptional regulator Fur. These import mechanisms are induced under iron-limiting conditions in vitro and during C. difficile infection of the host. This suggests that during a C. difficile infection, iron availability is limited in vivo.

Project description:In Pseudomonas aeruginosa, the ferric uptake regulator (Fur) protein controls both metabolism and virulence in response to iron availability. Differently from other bacteria, attempts to obtain fur deletion mutants of P. aeruginosa failed, leading to the assumption that Fur is an essential protein in this bacterium. By investigating a P. aeruginosa conditional fur mutant, we demonstrate that Fur is not essential for P. aeruginosa growth in liquid media, biofilm formation, and pathogenicity in an insect model of infection. Conversely, Fur is essential for growth on solid media since Fur-depleted cells are severely impaired in colony formation. Transposon-mediated random mutagenesis experiments identified pyochelin siderophore biosynthesis as a major cause of the colony growth defect of the conditional fur mutant, and deletion mutagenesis confirmed this evidence. Impaired colony growth of pyochelin-proficient Fur-depleted cells does not depend on oxidative stress, since Fur-depleted cells do not accumulate higher levels of reactive oxygen species (ROS) and are not rescued by antioxidant agents or overexpression of ROS-detoxifying enzymes. Ectopic expression of pch genes revealed that pyochelin production has no inhibitory effects on a fur deletion mutant of Pseudomonas syringae pv. tabaci, suggesting that the toxicity of the pch locus in Fur-depleted cells involves a P. aeruginosa-specific pathway(s).IMPORTANCE Members of the ferric uptake regulator (Fur) protein family are bacterial transcriptional repressors that control iron uptake and storage in response to iron availability, thereby playing a crucial role in the maintenance of iron homeostasis. While fur null mutants of many bacteria have been obtained, Fur appears to be essential in Pseudomonas aeruginosa for still unknown reasons. We obtained Fur-depleted P. aeruginosa cells by conditional mutagenesis and showed that Fur is dispensable for planktonic growth, while it is required for colony formation. This is because Fur protects P. aeruginosa colonies from toxicity exerted by the pyochelin siderophore. This work provides a functional basis to the essentiality of Fur in P. aeruginosa and highlights unique properties of the Fur regulon in this species.

Dataset Information

Iron-sulfur cluster assembly scaffold protein IscU is required for activation of ferric uptake regulator (Fur) in Escherichiacoli.

Publications

Iron-sulfur cluster assembly scaffold protein IscU is required for activation of ferric uptake regulator (Fur) in Escherichiacoli.

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