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Yanatori I, Kishi F, Toyokuni S. New iron export pathways acting via holo-ferritin secretion. Arch Biochem Biophys 2023; 746:109737. [PMID: 37683905 DOI: 10.1016/j.abb.2023.109737] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/30/2023] [Accepted: 09/02/2023] [Indexed: 09/10/2023]
Abstract
Ferritin is a spherical nanocage protein for iron storage, composed of 24 light- or heavy-polypeptide chain subunits. A single ferritin molecule can carry up to 4500 iron atoms in its core, which plays an important role in suppressing intracellular iron toxicity. Serum ferritin levels are used as a marker for the total amount of iron stored in the body. Most serum ferritin is iron-free (apo-ferritin) and it is unclear how ferritin is released from cells. Ferritin is secreted into serum via extracellular vesicles (EVs) or the secretory autophagy pathway but not via the classical endoplasmic reticulum (ER)-to-Golgi secretion pathway. We recently discovered that the level of tetraspanin CD63, a common EV marker, is post-transcriptionally regulated by the intracellular iron level and both CD63 and ferritin expression is induced by iron loading. Ferritin is incorporated into CD63(+)-EVs through the ferritin-specific autophagy adapter molecule, NCOA4, and then secreted from cells. EV production differs drastically depending on cell type and physiological conditions. Extracellular matrix detached cells express pentaspanin prominin 2 and prominin 2(+)-EVs secrete ferritin independently of NCOA4 trafficking. Ferritin is tightly bound to iron in EVs and functions as an iron-carrier protein in the extracellular environment. Cells can suppress ferroptosis by secreting holo-ferritin, which reduces intracellular iron concentration. However, this exposes the neighboring cells receiving the secreted holo-ferritin to a large excess of iron. This results in cellular toxicity through increased generation of reactive oxygen species (ROS). Here we review the machinery by which ferritin is incorporated into EVs and its role as an intercellular communication molecule.
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Affiliation(s)
- Izumi Yanatori
- Department of Molecular and Cellular Physiology, Graduate School of Medicine, Kyoto University, Kyoto, 606-8501, Japan.
| | - Fumio Kishi
- Kenjinkai Healthcare Corporation, Yamaguchi, 757-0001, Japan
| | - Shinya Toyokuni
- Department of Pathology and Biological Responses, Nagoya University Graduate School of Medicine, 65 Tsurumai-Cho, Showa-ku, Nagoya, 466-8550, Japan; Center for Low-temperature Plasma Sciences, Nagoya University, Furo-Cho, Chikusa-ku, Nagoya, 464-8603, Japan
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2
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Thirumalai A, Ganapathy Raman P, Jayavelu T, Subramanian R. Bridging the gap between maleate hydratase, citraconase and isopropylmalate isomerase: Insights into the single broad-specific enzyme. Enzyme Microb Technol 2023; 162:110140. [DOI: 10.1016/j.enzmictec.2022.110140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 09/23/2022] [Accepted: 10/08/2022] [Indexed: 11/13/2022]
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3
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Crystal structures of aconitase X enzymes from bacteria and archaea provide insights into the molecular evolution of the aconitase superfamily. Commun Biol 2021; 4:687. [PMID: 34099860 PMCID: PMC8184944 DOI: 10.1038/s42003-021-02147-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2020] [Accepted: 04/23/2021] [Indexed: 11/17/2022] Open
Abstract
Aconitase superfamily members catalyze the homologous isomerization of specific substrates by sequential dehydration and hydration and contain a [4Fe-4S] cluster. However, monomeric and heterodimeric types of function unknown aconitase X (AcnX) have recently been characterized as a cis-3-hydroxy-L-proline dehydratase (AcnXType-I) and mevalonate 5-phosphate dehydratase (AcnXType-II), respectively. We herein elucidated the crystal structures of AcnXType-I from Agrobacterium tumefaciens (AtAcnX) and AcnXType-II from Thermococcus kodakarensis (TkAcnX) without a ligand and in complex with substrates. AtAcnX and TkAcnX contained the [2Fe-2S] and [3Fe-4S] clusters, respectively, conforming to UV and EPR spectroscopy analyses. The binding sites of the [Fe-S] cluster and substrate were clearlydifferent from those that were completely conserved in other aconitase enzymes; however, theoverall structural frameworks and locations of active sites were partially similar to each other.These results provide novel insights into the evolutionary scenario of the aconitase superfamilybased on the recruitment hypothesis. Seiya Watanabe et al. report the crystal structures of two distinct members of the Aconitase X subfamily, which contain [Fe-S] clusters different from other aconitases. This study provides insight into the molecular evolution of the aconitase superfamily.
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Lächler K, Clauss K, Imhof J, Crocoll C, Schulz A, Halkier BA, Binder S. In Arabidopsis thaliana Substrate Recognition and Tissue- as Well as Plastid Type-Specific Expression Define the Roles of Distinct Small Subunits of Isopropylmalate Isomerase. FRONTIERS IN PLANT SCIENCE 2020; 11:808. [PMID: 32612621 PMCID: PMC7308503 DOI: 10.3389/fpls.2020.00808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Accepted: 05/19/2020] [Indexed: 06/11/2023]
Abstract
In Arabidopsis thaliana, the heterodimeric isopropylmalate isomerase (IPMI) is composed of a single large (IPMI LSU1) and one of three different small subunits (IPMI SSU1 to 3). The function of IPMI is defined by the small subunits. IPMI SSU1 is required for Leu biosynthesis and has previously also been proposed to be involved in the first cycle of Met chain elongation, the first phase of the synthesis of Met-derived glucosinolates. IPMI SSU2 and IPMI SSU3 participate in the Met chain elongation pathway. Here, we investigate the role of the three IPMI SSUs through the analysis of the role of the substrate recognition region spanning five amino acids on the substrate specificity of IPMI SSU1. Furthermore, we analyze in detail the expression pattern of fluorophore-tagged IPMI SSUs throughout plant development. Our study shows that the substrate recognition region that differs between IPMI SSU1 and the other two IMPI SSUs determines the substrate preference of IPMI. Expression of IPMI SSU1 is spatially separated from the expression of IPMI SSU2 and IPMI SSU3, and IPMI SSU1 is found in small plastids, whereas IMPI SSU2 and SSU3 are found in chloroplasts. Our data show a distinct role for IMPI SSU1 in Leu biosynthesis and for IMPI SSU2 and SSU3 in the Met chain elongation pathway.
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Affiliation(s)
- Kurt Lächler
- Institut für Molekulare Botanik, Fakultät für Naturwissenschaften, Universität Ulm, Ulm, Germany
| | - Karen Clauss
- Institut für Molekulare Botanik, Fakultät für Naturwissenschaften, Universität Ulm, Ulm, Germany
| | - Janet Imhof
- Institut für Molekulare Botanik, Fakultät für Naturwissenschaften, Universität Ulm, Ulm, Germany
| | - Christoph Crocoll
- DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Frederiksberg, Denmark
| | - Alexander Schulz
- DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Frederiksberg, Denmark
| | - Barbara Ann Halkier
- DynaMo Center, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Frederiksberg, Denmark
| | - Stefan Binder
- Institut für Molekulare Botanik, Fakultät für Naturwissenschaften, Universität Ulm, Ulm, Germany
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Functional characterization of aconitase X as a cis-3-hydroxy-L-proline dehydratase. Sci Rep 2016; 6:38720. [PMID: 27929065 PMCID: PMC5144071 DOI: 10.1038/srep38720] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Accepted: 11/11/2016] [Indexed: 01/30/2023] Open
Abstract
In the aconitase superfamily, which includes the archetypical aconitase, homoaconitase, and isopropylmalate isomerase, only aconitase X is not functionally annotated. The corresponding gene (LhpI) was often located within the bacterial gene cluster involved in L-hydroxyproline metabolism. Screening of a library of (hydroxy)proline analogues revealed that this protein catalyzes the dehydration of cis-3-hydroxy-L-proline to Δ1-pyrroline-2-carboxylate. Furthermore, electron paramagnetic resonance and site-directed mutagenic analyses suggests the presence of a mononuclear Fe(III) center, which may be coordinated with one glutamate and two cysteine residues. These properties were significantly different from those of other aconitase members, which catalyze the isomerization of α- to β-hydroxy acids, and have a [4Fe-4S] cluster-binding site composed of three cysteine residues. Bacteria with the LhpI gene could degrade cis-3-hydroxy-L-proline as the sole carbon source, and LhpI transcription was up-regulated not only by cis-3-hydroxy-L-proline, but also by several isomeric 3- and 4-hydroxyprolines.
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Tröße C, Kongshaug H, Dondrup M, Nilsen F. Characterisation of iron regulatory protein 1A and 1B in the blood-feeding copepod Lepeophtheirus salmonis. Exp Parasitol 2015; 157:1-11. [DOI: 10.1016/j.exppara.2015.06.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 04/21/2015] [Accepted: 06/15/2015] [Indexed: 11/29/2022]
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Vivar JC, Pemu P, McPherson R, Ghosh S. Redundancy control in pathway databases (ReCiPa): an application for improving gene-set enrichment analysis in Omics studies and "Big data" biology. OMICS-A JOURNAL OF INTEGRATIVE BIOLOGY 2013; 17:414-22. [PMID: 23758478 DOI: 10.1089/omi.2012.0083] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Abstract Unparalleled technological advances have fueled an explosive growth in the scope and scale of biological data and have propelled life sciences into the realm of "Big Data" that cannot be managed or analyzed by conventional approaches. Big Data in the life sciences are driven primarily via a diverse collection of 'omics'-based technologies, including genomics, proteomics, metabolomics, transcriptomics, metagenomics, and lipidomics. Gene-set enrichment analysis is a powerful approach for interrogating large 'omics' datasets, leading to the identification of biological mechanisms associated with observed outcomes. While several factors influence the results from such analysis, the impact from the contents of pathway databases is often under-appreciated. Pathway databases often contain variously named pathways that overlap with one another to varying degrees. Ignoring such redundancies during pathway analysis can lead to the designation of several pathways as being significant due to high content-similarity, rather than truly independent biological mechanisms. Statistically, such dependencies also result in correlated p values and overdispersion, leading to biased results. We investigated the level of redundancies in multiple pathway databases and observed large discrepancies in the nature and extent of pathway overlap. This prompted us to develop the application, ReCiPa (Redundancy Control in Pathway Databases), to control redundancies in pathway databases based on user-defined thresholds. Analysis of genomic and genetic datasets, using ReCiPa-generated overlap-controlled versions of KEGG and Reactome pathways, led to a reduction in redundancy among the top-scoring gene-sets and allowed for the inclusion of additional gene-sets representing possibly novel biological mechanisms. Using obesity as an example, bioinformatic analysis further demonstrated that gene-sets identified from overlap-controlled pathway databases show stronger evidence of prior association to obesity compared to pathways identified from the original databases.
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Affiliation(s)
- Juan C Vivar
- Biomedical Biotechnology Research Institute, North Carolina Central University, Durham, North Carolina, USA
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Manikandan K, Geerlof A, Zozulya AV, Svergun DI, Weiss MS. Structural studies on the enzyme complex isopropylmalate isomerase (LeuCD) fromMycobacterium tuberculosis. Proteins 2010; 79:35-49. [DOI: 10.1002/prot.22856] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 07/08/2010] [Accepted: 07/25/2010] [Indexed: 11/10/2022]
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9
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Banerjee S, Nandyala AK, Raviprasad P, Ahmed N, Hasnain SE. Iron-dependent RNA-binding activity of Mycobacterium tuberculosis aconitase. J Bacteriol 2007; 189:4046-52. [PMID: 17384188 PMCID: PMC1913386 DOI: 10.1128/jb.00026-07] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Cellular iron levels are closely monitored by iron regulatory and sensor proteins of Mycobacterium tuberculosis for survival inside macrophages. One such class of proteins systematically studied in eukaryotes and reported in a few prokaryotes are the iron-responsive proteins (IRPs). These IRPs bind to iron-responsive elements (IREs) present at untranslated regions (UTRs) of mRNAs and are responsible for posttranscriptional regulation of the expression of proteins involved in iron homeostasis. Amino acid sequence analysis of M. tuberculosis aconitase (Acn), a tricarboxylic acid (TCA) cycle enzyme, showed the presence of the conserved residues of the IRP class of proteins. We demonstrate that M. tuberculosis Acn is bifunctional. It is a monomeric protein that is enzymatically active in converting isocitrate to cis-aconitate at a broad pH range of 7 to 10 (optimum, pH 8). As evident from gel retardation assays, M. tuberculosis Acn also behaves like an IRP by binding to known mammalian IRE-like sequences and to predicted IRE-like sequences present at the 3' UTR of thioredoxin (trxC) and the 5' UTR of the iron-dependent repressor and activator (ideR) of M. tuberculosis. M. tuberculosis Acn when reactivated with Fe(2+) functions as a TCA cycle enzyme, but upon iron depletion by a specific iron chelator, it behaves like an IRP, binding to the selected IREs in vitro. Since iron is required for the Acn activity and inhibits the RNA-binding activity of Acn, the two activities of M. tuberculosis Acn are mutually exclusive. Our results demonstrate the bifunctional nature of M. tuberculosis Acn, pointing to its likely role in iron homeostasis.
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Wang J, Fillebeen C, Chen G, Biederbick A, Lill R, Pantopoulos K. Iron-dependent degradation of apo-IRP1 by the ubiquitin-proteasome pathway. Mol Cell Biol 2007; 27:2423-30. [PMID: 17242182 PMCID: PMC1899896 DOI: 10.1128/mcb.01111-06] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Iron regulatory protein 1 (IRP1) controls the translation or stability of several mRNAs by binding to "iron-responsive elements" within their untranslated regions. In iron-replete cells, IRP1 assembles a cubane iron-sulfur cluster (ISC) that inhibits RNA-binding activity and converts the protein to cytosolic aconitase. We show that the constitutive IRP1(C437S) mutant, which fails to form an ISC, is destabilized by iron. Thus, exposure of H1299 cells to ferric ammonium citrate reduced the half-life of transfected IRP1(C437S) from approximately 24 h to approximately 10 h. The iron-dependent degradation of IRP1(C437S) involved ubiquitination, required ongoing transcription and translation, and could be efficiently blocked by the proteasomal inhibitors MG132 and lactacystin. Similar results were obtained with overexpressed wild-type IRP1, which predominated in the apo-form even in iron-loaded H1299 cells, possibly due to saturation of the ISC assembly machinery. Importantly, inhibition of ISC biogenesis in HeLa cells by small interfering RNA knockdown of the cysteine desulfurase Nfs1 sensitized endogenous IRP1 for iron-dependent degradation. Collectively, these data uncover a mechanism for the regulation of IRP1 abundance as a means to control its RNA-binding activity, when the ISC assembly pathway is impaired.
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Affiliation(s)
- Jian Wang
- Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, 3755 Cote-Ste-Catherine Road, Montreal, Quebec H3T 1E2, Canada
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Wallander ML, Leibold EA, Eisenstein RS. Molecular control of vertebrate iron homeostasis by iron regulatory proteins. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:668-89. [PMID: 16872694 PMCID: PMC2291536 DOI: 10.1016/j.bbamcr.2006.05.004] [Citation(s) in RCA: 203] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Revised: 05/09/2006] [Accepted: 05/10/2006] [Indexed: 02/06/2023]
Abstract
Both deficiencies and excesses of iron represent major public health problems throughout the world. Understanding the cellular and organismal processes controlling iron homeostasis is critical for identifying iron-related diseases and in advancing the clinical treatments for such disorders of iron metabolism. Iron regulatory proteins (IRPs) 1 and 2 are key regulators of vertebrate iron metabolism. These RNA binding proteins post-transcriptionally control the stability or translation of mRNAs encoding proteins involved in iron homeostasis thereby controlling the uptake, utilization, storage or export of iron. Recent evidence provides insight into how IRPs selectively control the translation or stability of target mRNAs, how IRP RNA binding activity is controlled by iron-dependent and iron-independent effectors, and the pathological consequences of dysregulation of the IRP system.
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Affiliation(s)
- Michelle L. Wallander
- Department of Oncological Sciences, University of Utah, 15N. 2030E., Salt Lake City, UT 84112, USA
- Eccles Program in Human Molecular Biology and Genetics, University of Utah, 15N. 2030E., Salt Lake City, UT 84112, USA
| | - Elizabeth A. Leibold
- Department of Medicine, University of Utah, 15N. 2030E., Salt Lake City, UT 84112, USA
- Department of Oncological Sciences, University of Utah, 15N. 2030E., Salt Lake City, UT 84112, USA
- Eccles Program in Human Molecular Biology and Genetics, University of Utah, 15N. 2030E., Salt Lake City, UT 84112, USA
| | - Richard S. Eisenstein
- Department of Nutritional Sciences, University of Wisconsin, 1415 Linden Drive, Madison, WI 53706, USA
- Corresponding author. Tel.: +1 608 262 5830. E-mail address: (R.S. Eisenstein)
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12
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Nakano S, Fukaya M, Horinouchi S. Enhanced expression of aconitase raises acetic acid resistance inAcetobacter aceti. FEMS Microbiol Lett 2004. [DOI: 10.1111/j.1574-6968.2004.tb09605.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Lombo T, Takaya N, Miyazaki J, Gotoh K, Nishiyama M, Kosuge T, Nakamura A, Hoshino T. Functional analysis of the small subunit of the putative homoaconitase fromPyrococcus horikoshiiin theThermuslysine biosynthetic pathway. FEMS Microbiol Lett 2004. [DOI: 10.1111/j.1574-6968.2004.tb09498.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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14
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Wang J, Chen G, Muckenthaler M, Galy B, Hentze MW, Pantopoulos K. Iron-mediated degradation of IRP2, an unexpected pathway involving a 2-oxoglutarate-dependent oxygenase activity. Mol Cell Biol 2004; 24:954-65. [PMID: 14729944 PMCID: PMC321427 DOI: 10.1128/mcb.24.3.954-965.2004] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Iron regulatory protein 2 (IRP2), a central posttranscriptional regulator of cellular and systemic iron metabolism, undergoes proteasomal degradation in iron-replete cells. The prevailing model postulates that the mechanism involves site-specific oxidation of 3 cysteine residues (C168, C174, and C178) within a 73-amino-acid (73-aa) degradation domain. By expressing wild-type and mutated versions of IRP2 in H1299 cells, we find that a C168S C174S C178S triple mutant, or a deletion mutant lacking the entire "73-aa domain," is sensitive to iron-mediated degradation, like wild-type IRP2. The antioxidants N-acetylcysteine, ascorbate, and alpha-tocopherol not only fail to stabilize IRP2 but, furthermore, promote its proteasomal degradation. The pathway for IRP2 degradation is saturable, which may explain earlier data supporting the "cysteine oxidation model," and shows remarkable similarities with the degradation of the hypoxia-inducible factor 1 alpha (HIF-1 alpha): dimethyl-oxalylglycine, a specific inhibitor of 2-oxoglutarate-dependent oxygenases, stabilizes IRP2 following the administration of iron to iron-deficient cells. Our results challenge the current model for IRP2 regulation and provide direct pharmacological evidence for the involvement of 2-oxoglutarate-dependent oxygenases in a pathway for IRP2 degradation.
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Affiliation(s)
- Jian Wang
- Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada
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Makarova KS, Koonin EV. Filling a gap in the central metabolism of archaea: prediction of a novel aconitase by comparative-genomic analysis. FEMS Microbiol Lett 2004; 227:17-23. [PMID: 14568143 DOI: 10.1016/s0378-1097(03)00596-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Aconitase, an essential enzyme of the tricarboxylic acid cycle (TCA), so far has been identified only in a minority of archaeal genomes. This enzyme belongs to the aconitase A family, which is represented in most bacteria and eukaryotes. Using iterative sequence database search, we linked two previously uncharacterized protein families (COG1679 and COG1786), respectively, to the three Fe-S-cluster-associated aconitase domains and the swiveling domain, the four domains that are present in all known aconitase families. The respective genes are often found in one predicted operon and, moreover, are fused in several species, suggesting a functional and physical interaction. We predict that these proteins together comprise a previously undetected, distinct aconitase family, which we designated aconitase X. Aconitase X is encoded in the genomes of many archaea and some proteobacteria. Among archaea, the pattern of aconitase X occurrence complements that of aconitase A such that together the two enzymes account for aconitase activity in all archaea. Phylogenetic analysis indicates that aconitase X is likely to be the ancestral archaeal form, with non-orthologous displacement in some of the archaea apparently brought about by horizontal transfer of the gene for bacterial aconitase A. The prediction of aconitase X completes the TCA cycle for Methanothermobacter thermoautotrophicus and Archaeoglobus fulgidus and suggests that most archaea have a full TCA cycle.
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Affiliation(s)
- Kira S Makarova
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, 20894, USA.
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16
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Uhrigshardt H, Walden M, John H, Anemüller S. Purification and characterization of the first archaeal aconitase from the thermoacidophilicSulfolobus acidocaldarius. ACTA ACUST UNITED AC 2003. [DOI: 10.1046/j.1432-1327.2001.02049.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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17
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Zhang D, Dimopoulos G, Wolf A, Miñana B, Kafatos FC, Winzerling JJ. Cloning and molecular characterization of two mosquito iron regulatory proteins. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2002; 32:579-589. [PMID: 11891134 DOI: 10.1016/s0965-1748(01)00138-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Iron regulatory proteins (IRPs) control the synthesis of various proteins at the translational level by binding to iron responsive elements (IREs) in the mRNAs. Iron, infection, and stress can alter IRP/IRE binding activity. Insect messenger RNAs for ferritin and succinate dehydrogenase subunit b have IREs that are active translational control sites. We have cloned and sequenced cDNAs encoding proteins from the IRP1 family for the mosquitoes, Aedes aegypti and Anopheles gambiae. Both deduced amino acid sequences show substantial similarity to human IRP1 and Drosophila IRP1A and IRP1B, and all of the residues thought to be involved in aconitase activity and iron-sulfur cluster formation are conserved. Recombinant A. aegypti IRP1 binds to transcripts of the IREs of mosquito or human ferritin subunit mRNAs. No significant change in A. gambiae IRP1 messenger RNA could be detected during the various developmental stages of the life cycle, following iron loading by blood feeding, or after bacterial or parasitic infections. These data suggest that there is no change in gene transcription. Furthermore, bacterial challenge of A. gambiae cells did not change IRP1 protein levels. In contrast, IRP1 binding activity for the IRE was elevated following immune induction. These data show that changes in IRP1/IRE binding activity occur as part of the insect immune response.
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Affiliation(s)
- D Zhang
- Department of Nutritional Sciences, University of Arizona, Shantz 309, P.O. Box 210038, Tucson, AZ 85721-0038, USA
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Brazzolotto X, Timmins P, Dupont Y, Moulis JM. Structural changes associated with switching activities of human iron regulatory protein 1. J Biol Chem 2002; 277:11995-2000. [PMID: 11812787 DOI: 10.1074/jbc.m110938200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Metazoan iron regulatory protein 1 is a dual activity protein, being either an aconitase or a regulatory factor binding to messenger RNA involved in iron homeostasis. Sequence comparisons and site-directed mutagenesis experiments have supported a structural relationship between mitochondrial aconitase and iron regulatory protein 1. The structural properties of human recombinant iron regulatory protein 1 have been probed in the present work. Although iron-free iron regulatory protein 1 displays a significantly larger radius of gyration measured by small-angle neutron scattering than calculated for mitochondrial aconitase, binding of either the [4Fe-4S] cluster needed for aconitase activity or of a RNA substrate turns iron regulatory protein 1 into a more compact molecule. These conformational changes are associated with the gain of secondary structural elements as indicated by circular dichroism studies. They likely involve alpha-helices covering the substrate binding cleft of cytosolic aconitase, and they suggest an induced fit mechanism of iron-responsive element recognition. These studies refine previously proposed models of the "iron-sulfur switch" driving the biological function of human iron regulatory protein 1, and they provide a structural framework to probe the relevance of the numerous cellular molecules proposed to affect its function.
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Affiliation(s)
- Xavier Brazzolotto
- Commissariat à l'Energie Atomique-Grenoble, Département de Biologie Moléculaire et Structurale, 38054 Grenoble Cedex 9, France
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Heinzelmann E, Kienzlen G, Kaspar S, Recktenwald J, Wohlleben W, Schwartz D. The phosphinomethylmalate isomerase gene pmi, encoding an aconitase-like enzyme, is involved in the synthesis of phosphinothricin tripeptide in Streptomyces viridochromogenes. Appl Environ Microbiol 2001; 67:3603-9. [PMID: 11472937 PMCID: PMC93061 DOI: 10.1128/aem.67.8.3603-3609.2001] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Streptomyces viridochromogenes Tü494 produces the antibiotic phosphinothricin tripeptide (PTT). In the postulated biosynthetic pathway, one reaction, the isomerization of phosphinomethylmalate, resembles the aconitase reaction of the tricarboxylic acid (TCA) cycle. It was speculated that this reaction is carried out by the corresponding enzyme of the primary metabolism (C. J. Thompson and H. Seto, p. 197-222, in L. C. Vining and C. Stuttard, ed., Genetics and Biochemistry of Antibiotic Production, 1995). However, in addition to the TCA cycle aconitase gene, a gene encoding an aconitase-like protein (the phosphinomethylmalate isomerase gene, pmi) was identified in the PTT biosynthetic gene cluster by Southern hybridization experiments, using oligonucleotides which were derived from conserved amino acid sequences of aconitases. The deduced protein revealed high similarity to aconitases from plants, bacteria, and fungi and to iron regulatory proteins from eucaryotes. Pmi and the S. viridochromogenes TCA cycle aconitase, AcnA, have 52% identity. By gene insertion mutagenesis, a pmi mutant (Mapra1) was generated. The mutant failed to produce PTT, indicating the inability of AcnA to carry out the secondary-metabolism reaction. A His-tagged protein (Hispmi*) was heterologously produced in Streptomyces lividans. The purified protein showed no standard aconitase activity with citrate as a substrate, and the corresponding gene was not able to complement an acnA mutant. This indicates that Pmi and AcnA are highly specific for their respective enzymatic reactions.
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Affiliation(s)
- E Heinzelmann
- Mikrobiologie/Biotechnologie, Eberhard-Karls-Universität Tübingen, D-72076 Tübingen, Germany
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20
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Abstract
Mammalian iron homeostasis is maintained through the concerted action of sensory and regulatory networks that modulate the expression of proteins of iron metabolism at the transcriptional and/or post-transcriptional levels. Regulation of gene transcription provides critical developmental, cell cycle, and cell-type-specific controls on iron metabolism. Post-transcriptional control through the action of iron regulatory protein 1 (IRP1) and IRP2 coordinate the use of messenger RNA-encoding proteins that are involved in the uptake, storage, and use of iron in all cells of the body. IRPs may also provide a link between iron availability and cellular citrate use. Multiple factors, including iron, nitric oxide, oxidative stress, phosphorylation, and hypoxia/reoxygenation, influence IRP function. Recent evidence indicates that there is diversity in the function of the IRP system with respect to the response of specific IRPs to the same effector, as well as the selectivity with which IRPs modulate the use of specific messenger RNA.
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Affiliation(s)
- R S Eisenstein
- Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
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21
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Saas J, Ziegelbauer K, von Haeseler A, Fast B, Boshart M. A developmentally regulated aconitase related to iron-regulatory protein-1 is localized in the cytoplasm and in the mitochondrion of Trypanosoma brucei. J Biol Chem 2000; 275:2745-55. [PMID: 10644738 DOI: 10.1074/jbc.275.4.2745] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mitochondrial energy metabolism and Krebs cycle activities are developmentally regulated in the life cycle of the protozoan parasite Trypanosoma brucei. Here we report cloning of a T. brucei aconitase gene that is closely related to mammalian iron-regulatory protein 1 (IRP-1) and plant aconitases. Kinetic analysis of purified recombinant TbACO expressed in Escherichia coli resulted in a K(m) (isocitrate) of 3 +/- 0.4 mM, similar to aconitases of other organisms. This was unexpected since an arginine conserved in the aconitase protein family and crucial for substrate positioning in the catalytic center and for activity of pig mitochondrial aconitase (Zheng, L., Kennedy, M. C., Beinert, H., and Zalkin, H. (1992) J. Biol. Chem. 267, 7895-7903) is substituted by leucine in the TbACO sequence. Expression of the 98-kDa TbACO was shown to be lowest in the slender bloodstream stage of the parasite, 8-fold elevated in the stumpy stage, and increased a further 4-fold in the procyclic stage. The differential expression of TbACO protein contrasted with only minor changes in TbACO mRNA, indicating translational or post-translational mechanisms of regulation. Whereas animal cells express two distinct compartmentalized aconitases, mitochondrial aconitase and cytoplasmic aconitase/IRP-1, TbACO accounts for total aconitase activity in trypanosomes. By cell fractionation and immunofluorescence microscopy, we show that native as well as a transfected epitope-tagged TbACO localizes in both the mitochondrion (30%) and in the cytoplasm (70%). Together with phylogenetic reconstructions of the aconitase family, this suggests that animal IRPs have evolved from a multicompartmentalized ancestral aconitase. The possible functions of a cytoplasmic aconitase in trypanosomes are discussed.
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Affiliation(s)
- J Saas
- Arbeitsgruppe Molekulare Zellbiologie, Institut für Molekularbiologie und Biochemie und Institut für Infektionsmedizin, Freie Universität, Berlin, Germany
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22
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Schwartz D, Kaspar S, Kienzlen G, Muschko K, Wohlleben W. Inactivation of the tricarboxylic acid cycle aconitase gene from Streptomyces viridochromogenes Tü494 impairs morphological and physiological differentiation. J Bacteriol 1999; 181:7131-5. [PMID: 10559181 PMCID: PMC94190 DOI: 10.1128/jb.181.22.7131-7135.1999] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The tricarboxylic acid (TCA) cycle aconitase gene acnA from Streptomyces viridochromogenes Tü494 was cloned and analyzed. AcnA catalyzes the isomerization of citrate to isocitrate in the TCA cycle, as indicated by the ability of acnA to complement the aconitase-deficient Escherichia coli mutant JRG3259. An acnA mutant was unable to develop aerial mycelium and to sporulate, resulting in a bald phenotype. Furthermore, the mutant did not produce the antibiotic phosphinothricin tripeptide, demonstrating that AcnA also affects physiological differentiation.
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Affiliation(s)
- D Schwartz
- Mikrobiologie/Biotechnologie, Eberhard-Karls-Universität Tübingen, D-72076 Tübingen, Germany.
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23
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Brazzolotto X, Gaillard J, Pantopoulos K, Hentze MW, Moulis JM. Human cytoplasmic aconitase (Iron regulatory protein 1) is converted into its [3Fe-4S] form by hydrogen peroxide in vitro but is not activated for iron-responsive element binding. J Biol Chem 1999; 274:21625-30. [PMID: 10419470 DOI: 10.1074/jbc.274.31.21625] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Iron regulatory protein 1 (IRP1) regulates the synthesis of proteins involved in iron homeostasis by binding to iron-responsive elements (IREs) of messenger RNA. IRP1 is a cytoplasmic aconitase when it contains a [4Fe-4S] cluster and an RNA-binding protein after complete removal of the metal center by an unknown mechanism. Human IRP1, obtained as the pure recombinant [4Fe-4S] form, is an enzyme as efficient toward cis-aconitate as the homologous mitochondrial aconitase. The aconitase activity of IRP1 is rapidly lost by reaction with hydrogen peroxide as the [4Fe-4S] cluster is quantitatively converted into the [3Fe-4S] form with release of a single ferrous ion per molecule. The IRE binding capacity of IRP1 is not elicited with H(2)O(2). Ferrous sulfate (but not other more tightly coordinated ferrous ions, such as the complex with ethylenediamine tetraacetic acid) counteracts the inhibitory action of hydrogen peroxide on cytoplasmic aconitase, probably by replenishing iron at the active site. These results cast doubt on the ability of reactive oxygen species to directly increase IRP1 binding to IRE and support a signaling role for hydrogen peroxide in the posttranscriptional control of proteins involved in iron homeostasis in vivo.
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Affiliation(s)
- X Brazzolotto
- Département de Biologie Moléculaire et Structurale, Laboratoire Métalloprotéines, Commissariat à l'Energie Atomique, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France
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24
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A putative iron regulatory protein (IRP)-encoding cDNA sequence in the ciliate Eufolliculina uhligi, and differential gene expression during the life cycle. Eur J Protistol 1999. [DOI: 10.1016/s0932-4739(99)80040-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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25
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Huang TS, Melefors O, Lind MI, Söderhäll K. An atypical iron-responsive element (IRE) within crayfish ferritin mRNA and an iron regulatory protein 1 (IRP1)-like protein from crayfish hepatopancreas. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 1999; 29:1-9. [PMID: 10070739 DOI: 10.1016/s0965-1748(98)00097-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A putative crayfish iron-responsive element (IRE) is present in the 5'-untranslated region of the crayfish ferritin mRNA. The putative crayfish IRE is in a cap-proximal position and shares most of the structural features of the consensus IRE, but the RNA stem-loop structure contains a bulge of a guanine instead of a cytosine at the expected position, so far thought to be a hallmark of IREs. By using an electromobility shift assay this IRE was shown to specifically bind purified recombinant human iron regulatory protein 1 (IRP1) as well as a factor(s) present in a homogenate of crayfish hepatopancreas, likely to be a crayfish IRP1 homologue. With mutations in the crayfish IRE, the affinity of IRP to IRE was drastically decreased. A cDNA encoding an IRP1-like protein was cloned from the hepatopancreas of crayfish. This protein has sequence similarities to IRP, and contains all the active-site residues of aconitase, two putative RNA-binding regions and a putative contact site between RNA and IRP. These results show that a crayfish IRE, lacking the bulged C, can bind IRP1 in vitro and that an IRP1-like protein present in crayfish hepatopancreas may have both aconitase and RNA-binding activities.
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Affiliation(s)
- T S Huang
- Department of Physiological Mycology, University of Uppsala, Sweden
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26
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Pantopoulos K, Hentze MW. Activation of iron regulatory protein-1 by oxidative stress in vitro. Proc Natl Acad Sci U S A 1998; 95:10559-63. [PMID: 9724742 PMCID: PMC27933 DOI: 10.1073/pnas.95.18.10559] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Iron regulatory protein-1 (IRP-1), a central cytoplasmic regulator of cellular iron metabolism, is rapidly activated by oxidative stress to bind to mRNA iron-responsive elements. We have reconstituted the response of IRP-1 to extracellular H2O2 in a system derived from murine B6 fibroblasts permeabilized with streptolysin-O. This procedure allows separation of the cytosol from the remainder of the cells (cell pellet). IRP-1 in the cytosolic fraction fails to be directly activated by addition of H2O2. IRP-1 activation requires the presence of a nonsoluble, possibly membrane-associated component in the cell pellet. The streptolysin-O-based in vitro system faithfully recapitulates characteristic hallmarks of IRP-1 activation by H2O2 in intact cells. We show that the H2O2-mediated activation of IRP-1 is temperature dependent and sensitive to treatment with calf intestinal alkaline phosphatase (CIAP). Although IRP-1 activation is unaffected by addition of excess ATP or GTP to this in vitro system, it is negatively affected by the nonhydrolyzable nucleotide analogs adenylyl-imidodiphosphate and guanylyl-imidophosphate and completely blocked by ATP-gammaS and GTP-gammaS. The in vitro reconstitution of this oxidative stress-induced pathway has opened a different avenue for the biochemical dissection of the regulation of mammalian iron metabolism by oxidative stress. Our data show that H2O2 must be sensed to stimulate a pathway to activate IRP-1.
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Affiliation(s)
- K Pantopoulos
- European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
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27
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Kühn LC. Iron and gene expression: molecular mechanisms regulating cellular iron homeostasis. Nutr Rev 1998; 56:s11-9; discussion s54-75. [PMID: 9564172 DOI: 10.1111/j.1753-4887.1998.tb01681.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
In recent years, specific post-transcriptional mechanisms in the cytoplasm of vertebrate cells have been elucidated that directly affect the stability and translation of mRNAs coding for central proteins in iron metabolism. This review shall focus primarily on these mechanisms. Other levels of control, either affecting gene transcription and/ or related to the function of iron-capturing substances and transmembrane transport, are also likely to exist and to influence the iron balance and utilization. They are, however, much less clear.
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Affiliation(s)
- L C Kühn
- Swiss Institute for Experimental Cancer Research, Lausanne, Switzerland
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28
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Cunningham L, Gruer MJ, Guest JR. Transcriptional regulation of the aconitase genes (acnA and acnB) of Escherichia coli. MICROBIOLOGY (READING, ENGLAND) 1997; 143 ( Pt 12):3795-3805. [PMID: 9421904 DOI: 10.1099/00221287-143-12-3795] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Escherichia coli contains two differentially regulated aconitase genes, acnA and acnB. Two acnA promoters transcribing from start points located 407 bp (P1acnA) and 50 bp (P2acnA) upstream of the acnA coding region, and one acnB promoter (PacnB) with a start point 95 bp upstream of the acnB coding region, were identified by primer extension analysis. A 2.8 kb acnA monocistronic transcript was detected by Northern blot hybridization, but only in redox-stressed (methyl-viologen-treated) cultures, and a 2.5 kb acnB monocistronic transcript was detected in exponential- but not stationary-phase cultures. These findings are consistent with previous observations that acnA is specifically subject to SoxRS-mediated activation, whereas acnB encodes the major aconitase that is synthesized earlier in the growth cycle than AcnA. Further studies with acn-lacZ gene fusions and a wider range of transcription regulators indicated that acnA expression is initiated by sigma 38 from P1acnA, and from P2acnA it is activated directly or indirectly by CRP, FruR, Fur and SoxRS, and repressed by ArcA and FNR. In contrast, acnB expression is activated by CRP and repressed by ArcA, FruR and Fis from PacnB. Comparable studies with fum-lacZ fusions indicated that transcription of fumC, but not of fumA or fumB, is initiated by RNA polymerase containing sigma 38. It is concluded that AcnB is the major citric acid cycle enzyme, whereas AcnA is an aerobic stationary-phase enzyme that is specifically induced by iron and redox-stress.
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Affiliation(s)
- Louise Cunningham
- The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Megan J Gruer
- The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - John R Guest
- The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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29
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Costello LC, Liu Y, Franklin RB, Kennedy MC. Zinc inhibition of mitochondrial aconitase and its importance in citrate metabolism of prostate epithelial cells. J Biol Chem 1997; 272:28875-81. [PMID: 9360955 DOI: 10.1074/jbc.272.46.28875] [Citation(s) in RCA: 166] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Prostate epithelial cells possess a uniquely limiting mitochondrial (m-) aconitase activity that minimizes their ability to oxidize citrate. These cells also possess uniquely high cellular and mitochondrial zinc levels. Correlations among zinc, citrate, and m-aconitase in prostate indicated that zinc might be an inhibitor of prostate m-aconitase activity and citrate oxidation. The present studies reveal that zinc at near physiological levels inhibited m-aconitase activity of mitochondrial sonicate preparations obtained from rat ventral prostate epithelial cells. Corresponding studies conducted with mitochondrial sonicates of rat kidney cells revealed that zinc also inhibited the kidney m-aconitase activity. However the inhibitory effect of zinc was more sensitive with the prostate m-aconitase activity. Zinc inhibition fit the competitive inhibitor model. The inhibitory effect of zinc occurred only with citrate as substrate and was specific for the citrate --> cis-aconitate reaction. Other cations (Ca2+, Mn2+, Cd2+) did not result in the inhibitory effects obtained with zinc. The presence of endogenous zinc inhibited the m-aconitase activity of the prostate mitochondrial preparations. Kidney preparations that contain lower endogenous zinc levels exhibited no endogenous inhibition of m-aconitase activity. Studies with pig prostate and seminal vesicle mitochondrial preparations also revealed that zinc was a competitive inhibitor against citrate of m-aconitase activity. The effects of zinc on purified beef heart m-aconitase verified the competitive inhibitor action of zinc. In contrast, zinc had no inhibitory effect on purified cytosolic aconitase. These studies reveal for the first time that zinc is a specific inhibitor of m-aconitase of mammalian cells. In prostate epithelial cells, in situ mitochondrial zinc levels inhibit m-aconitase activity, which provides a mechanism by which citrate oxidation is limited.
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Affiliation(s)
- L C Costello
- Cellular and Molecular Biology Section/Oral Craniofacial and Biological Sciences, Dental School, University of Maryland, Baltimore, Maryland 21201, USA.
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30
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Gruer MJ, Bradbury AJ, Guest JR. Construction and properties of aconitase mutants of Escherichia coli. MICROBIOLOGY (READING, ENGLAND) 1997; 143 ( Pt 6):1837-1846. [PMID: 9202458 DOI: 10.1099/00221287-143-6-1837] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Escherichia coli contains two genes (acnA and acnB) encoding aconitase activities. An acnB mutant was engineered by replacing the chromosomal acnB gene by an internally deleted derivative containing a tetR cassette. An acnB double mutant was then made by transducing a previously constructed acnA::kanR mutation into the acnB::tetR strain. Western blotting confirmed that the AcnA and AcnB proteins were no longer produced by the corresponding mutants and PCR analysis showed that the chromosomal acnB gene had been replaced by the disrupted gene. Aerobic and anaerobic growth in glucose minimal medium were impaired but not abolished by the acnB mutation, indicating that the lesion is partially complemented by the acnA+ gene, and growth was enhanced by glutamate. The acnAB double mutant would not grow on unsupplemented glucose minimal medium and although it responded to glutamate like a typical auxotroph under anaerobic conditions, under aerobic conditions no response to glutamate was observed before it was over-grown by 'revertants' lacking citrate synthase (acnAB gltA). The acnAB double mutant retained a low but significant aconitase activity (< or = 5% of wild-type), designated AcnC. Enzymological and regulatory studies with acn-lacZ fusions indicated that AcnB is the major aconitase, which is synthesized earlier in the growth cycle than AcnA, and subject to catabolite and anaerobic repression.
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Affiliation(s)
- Megan J Gruer
- The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - Alan J Bradbury
- The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - John R Guest
- The Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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31
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Suzuki T, Inoki Y, Yamagishi A, Iwasaki T, Wakagi T, Oshima T. Molecular and phylogenetic characterization of isopropylmalate dehydrogenase of a thermoacidophilic archaeon, Sulfolobus sp. strain 7. J Bacteriol 1997; 179:1174-9. [PMID: 9023199 PMCID: PMC178813 DOI: 10.1128/jb.179.4.1174-1179.1997] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The archaeal leuB gene encoding isopropylmalate dehydrogenase of Sulfolobus sp. strain 7 was cloned, sequenced, and expressed in Escherichia coli. The recombinant Sulfolobus sp. enzyme was extremely stable to heat. The substrate and coenzyme specificities of the archaeal enzyme resembled those of the bacterial counterparts. Sedimentation equilibrium analysis supported an earlier proposal that the archaeal enzyme is homotetrameric, although the corresponding enzymes studied so far have been reported to be dimeric. Phylogenetic analyses suggested that the archaeal enzyme is homologous to mitochondrial NAD-dependent isocitrate dehydrogenases (which are tetrameric or octameric) as well as to isopropylmalate dehydrogenases from other sources. These results suggested that the present enzyme is the most primitive among isopropylmalate dehydrogenases belonging in the decarboxylating dehydrogenase family.
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Affiliation(s)
- T Suzuki
- Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan
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32
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Abstract
The aconitase family contains a diverse group of iron-sulphur (Fe-S) isomerases and two types of iron regulatory protein (IRP). Structural comparisons have revealed three architecturally distinct variants in which one of the four structural domains is covalently linked at either the amino- or carboxy-terminal end of a single polypeptide or else this domain exists as an independent subunit.
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Affiliation(s)
- M J Gruer
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, UK
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33
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Beinert H, Kennedy MC, Stout CD. Aconitase as Ironminus signSulfur Protein, Enzyme, and Iron-Regulatory Protein. Chem Rev 1996; 96:2335-2374. [PMID: 11848830 DOI: 10.1021/cr950040z] [Citation(s) in RCA: 422] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Helmut Beinert
- Institute for Enzyme Research, Graduate School, and Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53705, Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037
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