IscA Mediates Iron Delivery for Assembly of Iron-Sulfur Clusters in IscU under the Limited Accessible Free Iron Conditions

Ding, Huangen; Clark, R. J. H.; Ding, Baojin

doi:10.1074/jbc.m404533200

Cited by 94 publications

(102 citation statements)

References 41 publications

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“…The bacterial protein IscA is a product of the isc operon, which is involved in the assembly of iron-sulfur clusters (3). The specific role of IscA in this pathway in E. coli has been a matter of substantial debate, and it has been proposed that IscA serves either as an iron donor or as a scaffold for iron-sulfur cluster assembly (9,10). That being said, the importance of IscA in the bacterial iron-sulfur cluster assembly pathway and our previous work identifying a role for IOP1 in cytosolic iron-sulfur cluster assembly in mammalian cells lead us to investigate human IscA1 in more detail.…”

Section: Resultsmentioning

confidence: 99%

“…For example, IscU has been proposed to be a scaffold of iron-sulfur cluster assembly in E. coli, S. cerevisiae, and mammals (4 -6). IscA has been proposed to serve as a scaffold for delivering iron-sulfur clusters to select target proteins in E. coli and S. cerevisiae or, alternatively, as an iron donor in E. coli (7)(8)(9)(10); its role in mammalian cells is not known.…”

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confidence: 99%

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Human ISCA1 Interacts with IOP1/NARFL and Functions in Both Cytosolic and Mitochondrial Iron-Sulfur Protein Biogenesis

Song

Lee

2009

Journal of Biological Chemistry

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Iron-sulfur proteins play an essential role in many biologic processes. Hence, understanding their assembly is an important goal. In Escherichia coli, the protein IscA is a product of the isc (iron-sulfur cluster) operon and functions in the iron-sulfur cluster assembly pathway in this organism. IscA is conserved in evolution, but its function in mammalian cells is not known. Here, we provide evidence for a role for a human homologue of IscA, named IscA1, in iron-sulfur protein biogenesis. We observe that small interfering RNA knockdown of IscA1 in HeLa cells leads to decreased activity of two mitochondrial iron-sulfur enzymes, succinate dehydrogenase and mitochondrial aconitase, as well as a cytosolic iron-sulfur enzyme, cytosolic aconitase. IscA1 is observed both in cytosolic and mitochondrial fractions. We find that IscA1 interacts with IOP1 (iron-only hydrogenase-like protein 1)/NARFL (nuclear prelamin A recognition factor-like), a cytosolic protein that plays a role in the cytosolic iron-sulfur protein assembly pathway. We therefore propose that human IscA1 plays an important role in both mitochondrial and cytosolic iron-sulfur cluster biogenesis, and a notable component of the latter is the interaction between IscA1 and IOP1.Iron-sulfur proteins play essential roles in pathways that include the Krebs cycle, oxidative phosphorylation, gene regulation, and purine metabolism (1, 2). Their assembly presents particular challenges in that iron is readily oxidized and can generate free radicals. Hence, there are specific pathways that participate in the assembly of iron-sulfur clusters. In bacteria such as Escherichia coli, there is a pathway dedicated to the assembly of iron-sulfur clusters (3). The isc operon is the central genetic locus for this pathway, and it contains genes that encode for the proteins that include IscS, IscU, and IscA. The key elements of this pathway include a mechanism for obtaining sulfur through the enzymatic activity of a cysteine desulfurase, a mechanism for combining sulfur with iron on scaffold proteins, and a means for delivery of the resultant iron-sulfur clusters to target apoproteins. It appears that these key elements have been conserved through evolution. Thus, the E. coli cysteine desulfurase IscS has homologues in Saccharomyces cerevisiae and mammalian cells, indicative of a central conserved function. Moreover, homologues of IscU and IscA also exist in yeast and mammalian cells. The exact function of these is less certain. For example, IscU has been proposed to be a scaffold of iron-sulfur cluster assembly in E. coli, S. cerevisiae, and mammals (4 -6). IscA has been proposed to serve as a scaffold for delivering iron-sulfur clusters to select target proteins in E. coli and S. cerevisiae or, alternatively, as an iron donor in E. coli (7-10); its role in mammalian cells is not known.In eukaryotic cells, the situation is made more complex by the necessity of having to assemble both mitochondrial and cytosolic iron-sulfur clusters. In S. cerevisiae, there are proteins dedicated...

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Human ISCA1 Interacts with IOP1/NARFL and Functions in Both Cytosolic and Mitochondrial Iron-Sulfur Protein Biogenesis

Song

Lee

2009

Journal of Biological Chemistry

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“…Hence, we might expect a great diversity in the way bacteria make use of otherwise conserved components to carry out Fe-S biogenesis. Another challenge to the view of A-type proteins as scaffolds comes from in vitro investigations, which concluded that A-type proteins could be simple iron donors (30)(31)(32)(33)(34). Interestingly, the erpA gene is part of a chromosomal region that is particularly rich in iron uptake-related genes.…”

Section: Discussionmentioning

confidence: 99%

“…Three conserved Cys residues could act as ligands for these clusters, as indicated by mutagenesis studies and by the recently obtained 3D structure of IscA (26)(27)(28)(29). However, the proposal that IscA/SufA acts as a scaffold was challenged by in vitro studies, which suggest that A-type proteins act as iron chaperones, and by the fact that mutations in iscA or sufA did not yield major physiological defects (30)(31)(32)(33)(34)(35)(36). Noticeably, however, in A. vinelandii, iscA appeared to be required at high concentrations of oxygen (37).…”

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confidence: 99%

ErpA, an iron–sulfur (Fe–S) protein of the A-type essential for respiratory metabolism in Escherichia coli

Loiseau

Gerez

Bekker

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

135

149

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Understanding the biogenesis of iron-sulfur (Fe-S) proteins is relevant to many fields, including bioenergetics, gene regulation, and cancer research. Several multiprotein complexes assisting Fe-S assembly have been identified in both prokaryotes and eukaryotes. Here, we identify in Escherichia coli an A-type Fe-S protein that we named ErpA. Remarkably, erpA was found essential for growth of E. coli in the presence of oxygen or alternative electron acceptors. It was concluded that isoprenoid biosynthesis was impaired by the erpA mutation. First, the eukaryotic mevalonate-dependent pathway for biosynthesis of isopentenyl diphosphate restored the respiratory defects of an erpA mutant. Second, the erpA mutant contained a greatly reduced amount of ubiquinone and menaquinone. Third, ErpA bound Fe-S clusters and transferred them to apo-IspG, a protein catalyzing isopentenyl diphosphate biosynthesis in E. coli. Surprisingly, the erpA gene maps at a distance from any other Fe-S biogenesis-related gene. ErpA is an A-type Fe-S protein that is characterized by an essential role in cellular metabolism.essential gene yadR ͉ isoprenoid ͉ respiration ͉ scaffold

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“…1). IscA is a nonessential protein encoded within the ISC transcriptional unit, and it has been proposed to serve as an alternative [Fe-S] cluster assembly scaffold (10 -12) or as an iron donor during the [Fe-S] cluster assembly process (13). IscA contains three cysteine residues that are essential for its physiological function (3).…”

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confidence: 99%

A Proposed Role for the Azotobacter vinelandii NfuA Protein as an Intermediate Iron-Sulfur Cluster Carrier

Bandyopadhyay

Naik

O’Carroll

et al. 2008

Journal of Biological Chemistry

129

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Iron-sulfur clusters ([Fe-The in vivo maturation of simple [Fe-S] proteins is proposed to require preassembly of [Fe-S] species on molecular scaffolds. The first [Fe-S] cluster assembly system to be described is the NIF 2 system from Azotobacter vinelandii. This system consists of a cysteine desulfurase, encoded by nifS, which supplies the S for [Fe-S] cluster formation, and a proposed scaffold protein, encoded by nifU (1). The NIF system is specialized for the maturation of [Fe-S] proteins involved in nitrogen fixation.A. vinelandii also contains a second [Fe-S] protein maturation system designated ISC. The ISC system is required for the general maturation of cellular [Fe-S] proteins involved in intermediary metabolism, such as aconitase (2). The ISC system is more complicated than the NIF system as it includes the products of eight contiguous genes : iscR, iscS, iscU, iscA, hscB, hscA, fdx, and iscX (3). Although the NIF and ISC systems exhibit physiological target specificity, each can partially replace the function of the other, when expressed at high levels (4, 5).Even though the NIF and ISC systems are differentiated by their apparent target specificities, they share a number of common structural and functional features. For example, NifS and IscS have similar sequences, and they both exhibit cysteine desulfurase activity (2). IscU also shares considerable sequence identity when compared with the N-terminal domain of NifU, including conservation of three cysteine residues that are likely to provide the nucleation site(s) for [Fe-S] cluster assembly (2, 6).NifU is a modular protein that contains three distinct domains (Fig. 1). The central domain contains a stable redoxactive [2Fe-2S] cluster with an as-yet-unknown function (7). In vitro and in vivo experiments have established that labile [Fe-S] clusters can be assembled on both the N-terminal and C-terminal domains of NifU, and such cluster-loaded forms of NifU can be used for activation of the nitrogenase 9). Thus, NifU contains two different sites upon which labile [Fe-S] clusters can be assembled in vitro, but the functional relationship between these sites is not yet known.There are no genes within the ISC transcriptional unit that encode proteins with sequence similarity to the C-terminal domain of NifU. However, located elsewhere on the A. vinelandii genome is a gene, designated nfuA, whose product encodes a protein having a C-terminal sequence similar to the C-terminal domain of NifU (Fig. 1). The sequence conservation between NifU and NfuA includes two cysteine residues that are required for the in vitro assembly of [Fe-S] clusters within the NifU C-terminal domain. Like NifU, NfuA also appears to be a modular protein because the amino acid sequence within its N-terminal region shares some sequence similarity with another protein involved in [Fe-S] protein maturation designated IscA (Fig. 1). IscA is a nonessential protein encoded within the ISC transcriptional unit, and it has been proposed to serve as an alternative [Fe-S] cluster ass...

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IscA Mediates Iron Delivery for Assembly of Iron-Sulfur Clusters in IscU under the Limited Accessible Free Iron Conditions

Cited by 94 publications

References 41 publications

Human ISCA1 Interacts with IOP1/NARFL and Functions in Both Cytosolic and Mitochondrial Iron-Sulfur Protein Biogenesis

Human ISCA1 Interacts with IOP1/NARFL and Functions in Both Cytosolic and Mitochondrial Iron-Sulfur Protein Biogenesis

ErpA, an iron–sulfur (Fe–S) protein of the A-type essential for respiratory metabolism in Escherichia coli

A Proposed Role for the Azotobacter vinelandii NfuA Protein as an Intermediate Iron-Sulfur Cluster Carrier

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