Publications by authors named "Simona Todisco"

15 Publications

  • Page 1 of 1

Hydrosol: Untargeted Metabolomic Analysis and Anti-Inflammatory Activity Mediated by NF-B and the Citrate Pathway.

Oxid Med Cell Longev 2020 1;2020:4264815. Epub 2020 Nov 1.

Department of Science, University of Basilicata, Viale dell'Ateneo Lucano, 10, 85100 Potenza, Italy.

shows a long range of biological activities, and it has been used in traditional medicine for treatment of various kinds of diseases. Moreover, related essential oil keeps important health-promoting properties. However, less is known about hydrosol, a main by-product of essential oil production, usually used for steam distillation itself or discarded. In this work, by using ultra-high-resolution ESI(+)-FT-ICR mass spectrometry, a direct identification of four main classes of metabolites of hydrosol (i.e., terpenes, amino acids, peptides, and condensed heterocycles) was obtained. Remarkably, hydrosol exhibited an anti-inflammatory activity by suppressing the secretion of IL-1, IL-6, and TNF- proinflammatory cytokines in lipopolysaccharide- (LPS-) activated primary human monocytes. In LPS-triggered U937 cells, it inhibited NF-B, a key transcription factor in inflammatory cascade, regulating the expression of both the mitochondrial citrate carrier and the ATP citrate lyase genes. These two main components of the citrate pathway were downregulated by hydrosol. Therefore, the levels of ROS, NO, and PGE, the inflammatory mediators downstream the citrate pathway, were reduced. Results shed light on metabolic profile and anti-inflammatory properties of hydrosol, suggesting its potential as a therapeutic agent.
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http://dx.doi.org/10.1155/2020/4264815DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7652607PMC
November 2020

Glufosinate constrains synchronous and metachronous metastasis by promoting anti-tumor macrophages.

EMBO Mol Med 2020 10 4;12(10):e11210. Epub 2020 Sep 4.

Laboratory of Tumor Inflammation and Angiogenesis, Center for Cancer Biology (CCB), VIB, Leuven, Belgium.

Glutamine synthetase (GS) generates glutamine from glutamate and controls the release of inflammatory mediators. In macrophages, GS activity, driven by IL10, associates to the acquisition of M2-like functions. Conditional deletion of GS in macrophages inhibits metastasis by boosting the formation of anti-tumor, M1-like, tumor-associated macrophages (TAMs). From this basis, we evaluated the pharmacological potential of GS inhibitors in targeting metastasis, identifying glufosinate as a specific human GS inhibitor. Glufosinate was tested in both cultured macrophages and on mice bearing metastatic lung, skin and breast cancer. We found that glufosinate rewires macrophages toward an M1-like phenotype both at the primary tumor and metastatic site, countering immunosuppression and promoting vessel sprouting. This was also accompanied to a reduction in cancer cell intravasation and extravasation, leading to synchronous and metachronous metastasis growth inhibition, but no effects on primary tumor growth. Glufosinate treatment was well-tolerated, without liver and brain toxicity, nor hematopoietic defects. These results identify GS as a druggable enzyme to rewire macrophage functions and highlight the potential of targeting metabolic checkpoints in macrophages to treat cancer metastasis.
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http://dx.doi.org/10.15252/emmm.201911210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7539200PMC
October 2020

TCA Cycle Rewiring as Emerging Metabolic Signature of Hepatocellular Carcinoma.

Cancers (Basel) 2019 Dec 25;12(1). Epub 2019 Dec 25.

Department of Science, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.

Hepatocellular carcinoma (HCC) is a common malignancy. Despite progress in treatment, HCC is still one of the most lethal cancers. Therefore, deepening molecular mechanisms underlying HCC pathogenesis and development is required to uncover new therapeutic strategies. Metabolic reprogramming is emerging as a critical player in promoting tumor survival and proliferation to sustain increased metabolic needs of cancer cells. Among the metabolic pathways, the tricarboxylic acid (TCA) cycle is a primary route for bioenergetic, biosynthetic, and redox balance requirements of cells. In recent years, a large amount of evidence has highlighted the relevance of the TCA cycle rewiring in a variety of cancers. Indeed, aberrant gene expression of several key enzymes and changes in levels of critical metabolites have been observed in many solid human tumors. In this review, we summarize the role of the TCA cycle rewiring in HCC by reporting gene expression and activity dysregulation of enzymes relating not only to the TCA cycle but also to glutamine metabolism, malate/aspartate, and citrate/pyruvate shuttles. Regarding the transcriptional regulation, we focus on the link between NF-κB-HIF1 transcriptional factors and TCA cycle reprogramming. Finally, the potential of metabolic targets for new HCC treatments has been explored.
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http://dx.doi.org/10.3390/cancers12010068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7016696PMC
December 2019

Transcriptional Regulation Factors of the Human Mitochondrial Aspartate/Glutamate Carrier Gene, Isoform 2 (): USF1 as Basal Factor and FOXA2 as Activator in Liver Cells.

Int J Mol Sci 2019 Apr 16;20(8). Epub 2019 Apr 16.

Department of Science, University of Basilicata, 85100 Potenza, Italy.

Mitochondrial carriers catalyse the translocation of numerous metabolites across the inner mitochondrial membrane, playing a key role in different cell functions. For this reason, mitochondrial carrier gene expression needs tight regulation. The human gene, encoding for the mitochondrial aspartate/glutamate carrier isoform 2 (AGC2), catalyses the electrogenic exchange of aspartate for glutamate plus a proton, thus taking part in many metabolic processes including the malate-aspartate shuttle. By the luciferase (LUC) activity of promoter deletion constructs we identified the putative promoter region, comprising the proximal promoter (-442 bp/-19 bp), as well as an enhancer region (-968 bp/-768 bp). Furthermore, with different approaches, such as in silico promoter analysis, gene silencing and chromatin immunoprecipitation, we identified two transcription factors responsible for transcriptional regulation: FOXA2 and USF1. USF1 acts as a positive transcription factor which binds to the basal promoter thus ensuring gene expression in a wide range of tissues. The role of FOXA2 is different, working as an activator in hepatic cells. As a tumour suppressor, FOXA2 could be responsible for high expression levels in liver and its downregulation in hepatocellular carcinoma (HCC).
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http://dx.doi.org/10.3390/ijms20081888DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6515469PMC
April 2019

Epigenetic upregulation and functional role of the mitochondrial aspartate/glutamate carrier isoform 1 in hepatocellular carcinoma.

Biochim Biophys Acta Mol Basis Dis 2019 01 12;1865(1):38-47. Epub 2018 Oct 12.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, via Orabona 4, 70125 Bari, Italy. Electronic address:

Metabolic reprogramming is a common hallmark of cancer cells. Although some biochemical features have been clarified, there is still much to learn about cancer cell metabolism and its regulation. Aspartate-glutamate carrier isoform 1 (AGC1), encoded by SLC25A12 gene, catalyzes an exchange between intramitochondrial aspartate and cytosolic glutamate plus a proton across the mitochondrial membrane, so supplying aspartate to the cytosol. SLC25A12, expressed in brain, heart, and skeletal muscle, is silenced in normal liver. Here, we demonstrate that SLC25A12 gene is reactivated in hepatocellular carcinoma (HCC) HepG2 cell line through histone acetylation and CREB recruitment. Furthermore, SLC25A12 knockdown by small interfering RNA, impairs HepG2 cell proliferation by inducing cell cycle arrest. AGC1 sustains HCC cell growth by supplying cytosolic aspartate for nucleotide biosynthesis. In addition, SLC25A12-silenced HCC cells show a strong reduction of cell migration. Overall, we have provided evidence for molecular mechanisms controlling SLC25A12 gene expression in liver and pointing to an important role for AGC1 in HCC.
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http://dx.doi.org/10.1016/j.bbadis.2018.10.018DOI Listing
January 2019

Identification of new highly selective inhibitors of the human ADP/ATP carriers by molecular docking and in vitro transport assays.

Biochem Pharmacol 2016 Jan 23;100:112-32. Epub 2015 Nov 23.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Orabona 4, 70125 Bari, Italy. Electronic address:

Mitochondrial carriers are proteins that shuttle a variety of metabolites, nucleotides and coenzymes across the inner mitochondrial membrane. The mitochondrial ADP/ATP carriers (AACs) specifically translocate the ATP synthesized within mitochondria to the cytosol in exchange for the cytosolic ADP, playing a key role in energy production, in promoting cell viability and regulating mitochondrial permeability transition pore opening. In Homo sapiens four genes code for AACs with different tissue distribution and expression patterns. Since AACs are dysregulated in several cancer types, the employment of known and new AAC inhibitors might be crucial for inducing mitochondrial-mediated apoptosis in cancer cells. Albeit carboxyatractyloside (CATR) and bongkrekic acid (BKA) are known to be powerful and highly selective AAC inhibitors, able to induce mitochondrial dysfunction at molecular level and poisoning at physiological level, we estimated here for the first time their affinity for the human recombinant AAC2 by in vitro transport assays. We found that the inhibition constants of CATR and BKA are 4 nM and 2.0 μM, respectively. For finding new AAC inhibitors we also performed a docking-based virtual screening of an in-house developed chemical library and we identified about 100 ligands showing high affinity for the AAC2 binding region. By testing 13 commercially available molecules, out of the 100 predicted candidates, we found that 2 of them, namely suramin and chebulinic acid, are competitive AAC2 inhibitors with inhibition constants 0.3 μM and 2.1 μM, respectively. We also demonstrated that chebulinic acid and suramin are "highly selective" AAC2 inhibitors, since they poorly inhibit other human mitochondrial carriers (namely ORC1, APC1 and AGC1).
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http://dx.doi.org/10.1016/j.bcp.2015.11.019DOI Listing
January 2016

The human SLC25A33 and SLC25A36 genes of solute carrier family 25 encode two mitochondrial pyrimidine nucleotide transporters.

J Biol Chem 2014 Nov 15;289(48):33137-48. Epub 2014 Oct 15.

From the Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, via Orabona 4, 70125 Bari, Italy, Center of Excellence in Comparative Genomics, University of Bari, via Orabona 4, 70125 Bari, Italy

The human genome encodes 53 members of the solute carrier family 25 (SLC25), also called the mitochondrial carrier family, many of which have been shown to transport inorganic anions, amino acids, carboxylates, nucleotides, and coenzymes across the inner mitochondrial membrane, thereby connecting cytosolic and matrix functions. Here two members of this family, SLC25A33 and SLC25A36, have been thoroughly characterized biochemically. These proteins were overexpressed in bacteria and reconstituted in phospholipid vesicles. Their transport properties and kinetic parameters demonstrate that SLC25A33 transports uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates by an antiport mechanism and SLC25A36 cytosine and uracil (deoxy)nucleoside mono-, di-, and triphosphates by uniport and antiport. Both carriers also transported guanine but not adenine (deoxy)nucleotides. Transport catalyzed by both carriers was saturable and inhibited by mercurial compounds and other inhibitors of mitochondrial carriers to various degrees. In confirmation of their identity (i) SLC25A33 and SLC25A36 were found to be targeted to mitochondria and (ii) the phenotypes of Saccharomyces cerevisiae cells lacking RIM2, the gene encoding the well characterized yeast mitochondrial pyrimidine nucleotide carrier, were overcome by expressing SLC25A33 or SLC25A36 in these cells. The main physiological role of SLC25A33 and SLC25A36 is to import/export pyrimidine nucleotides into and from mitochondria, i.e. to accomplish transport steps essential for mitochondrial DNA and RNA synthesis and breakdown.
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http://dx.doi.org/10.1074/jbc.M114.610808DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4246075PMC
November 2014

Distance-dependent hydrophobic-hydrophobic contacts in protein folding simulations.

Phys Chem Chem Phys 2014 Sep;16(35):18907-17

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Via Orabona 4, 70125, Bari, Italy.

Successful prediction of protein folding from an amino acid sequence is a challenge in computational biology. In order to reveal the geometric constraints that drive protein folding, highlight those constraints kept or missed by distinct lattices and for establishing which class of intra- and inter-secondary structure element interactions is the most relevant for the correct folding of proteins, we have calculated inter-alpha carbon distances in a set of 42 crystal structures consisting of mainly helix, sheet or mixed conformations. The inter-alpha carbon distances were also calculated in several lattice "hydrophobic-polar" models built from the same protein set. We found that helix structures are more prone to form "hydrophobic-hydrophobic" contacts than beta-sheet structures. At a distance lower than or equal to 3.8 Å (very short-range interactions), "hydrophobic-hydrophobic" contacts are almost absent in the native structures, while they are frequent in all the analyzed lattice models. At distances in-between 3.8 and 9.5 Å (short-/medium-range interactions), the best performing lattice for reproducing mainly helix structures is the body-centered-cubic lattice. If protein structures contain sheet portions, lattice performances get worse, with few exceptions observed for double-tetrahedral and body-centered-cubic lattices. Finally, we can observe that ab initio protein folding algorithms, i.e. those based on the employment of lattices and Monte Carlo simulated annealings, can be improved simply and effectively by preventing the generation of "hydrophobic-hydrophobic" contacts shorter than 3.8 Å, by monitoring the "hydrophobic-hydrophobic/polar-polar" contact ratio in short-/medium distance ranges and by using preferentially a body-centered-cubic lattice.
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http://dx.doi.org/10.1039/c4cp01131gDOI Listing
September 2014

The Saccharomyces cerevisiae gene YPR011c encodes a mitochondrial transporter of adenosine 5'-phosphosulfate and 3'-phospho-adenosine 5'-phosphosulfate.

Biochim Biophys Acta 2014 Feb 1;1837(2):326-34. Epub 2013 Dec 1.

Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, via Orabona 4, 70125 Bari, Italy; Center of Excellence in Comparative Genomics, University of Bari, Italy. Electronic address:

The genome of Saccharomyces cerevisiae contains 35 members of the mitochondrial carrier family, nearly all of which have been functionally characterized. In this study, the identification of the mitochondrial carrier for adenosine 5'-phosphosulfate (APS) is described. The corresponding gene (YPR011c) was overexpressed in bacteria. The purified protein was reconstituted into phospholipid vesicles and its transport properties and kinetic parameters were characterized. It transported APS, 3'-phospho-adenosine 5'-phosphosulfate, sulfate and phosphate almost exclusively by a counter-exchange mechanism. Transport was saturable and inhibited by bongkrekic acid and other inhibitors. To investigate the physiological significance of this carrier in S. cerevisiae, mutants were subjected to thermal shock at 45°C in the presence of sulfate and in the absence of methionine. At 45°C cells lacking YPR011c, engineered cells (in which APS is produced only in mitochondria) and more so the latter cells, in which the exit of mitochondrial APS is prevented by the absence of YPR011cp, were less thermotolerant. Moreover, at the same temperature all these cells contained less methionine and total glutathione than wild-type cells. Our results show that S. cerevisiae mitochondria are equipped with a transporter for APS and that YPR011cp-mediated mitochondrial transport of APS occurs in S. cerevisiae under thermal stress conditions.
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http://dx.doi.org/10.1016/j.bbabio.2013.11.013DOI Listing
February 2014

Statins, fibrates and retinoic acid upregulate mitochondrial acylcarnitine carrier gene expression.

Biochem Biophys Res Commun 2009 Oct 6;388(4):643-7. Epub 2009 Aug 6.

Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Bari, Italy.

In this study, we investigated the effects of statins, fibrates, 9-cis-retinoic acid and forskolin on the transcription of the mitochondrial carnitine/acylcarnitine carrier (CAC) gene. Statins, fibrates, retinoic acid and forskolin activate luciferase gene reporter activity driven by the -334/+3 bp region of the human CAC promoter containing wild-type (but not mutated) PPRE. These four agents also increase CAC transcript and protein levels. The combinations of statins and fibrates, retinoic acid and fibrates and fibrates and forskolin act synergistically. Mevalonate abolishes the activation of CAC gene expression by statins; the inhibitor of the PKA pathway H89 suppresses the stimulation of CAC gene expression by forskolin. Because CAC is essential for fatty acid beta-oxidation, the above results on the regulation of CAC gene expression provide a novel contribution to the understanding of the hypolipidemic action of statins, fibrates and retinoic acid.
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http://dx.doi.org/10.1016/j.bbrc.2009.08.008DOI Listing
October 2009

A novel member of solute carrier family 25 (SLC25A42) is a transporter of coenzyme A and adenosine 3',5'-diphosphate in human mitochondria.

J Biol Chem 2009 Jul 8;284(27):18152-9. Epub 2009 May 8.

Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Italy.

Mitochondrial carriers are a family of proteins that transport metabolites, nucleotides, and cofactors across the inner mitochondrial membrane thereby connecting cytosolic and matrix functions. The essential cofactor coenzyme A (CoA) is synthesized outside the mitochondrial matrix and therefore must be transported into mitochondria where it is required for a number of fundamental processes. In this work we have functionally identified and characterized SLC25A42, a novel human member of the mitochondrial carrier family. The SLC25A42 gene (Haitina, T., Lindblom, J., Renström, T., and Fredriksson, R., 2006, Genomics 88, 779-790) was overexpressed in Escherichia coli, purified, and reconstituted into phospholipid vesicles. Its transport properties, kinetic parameters, and targeting to mitochondria demonstrate that SLC25A42 protein is a mitochondrial transporter for CoA and adenosine 3',5'-diphosphate. SLC25A42 catalyzed only a counter-exchange transport, exhibited a high transport affinity for CoA, dephospho-CoA, ADP, and adenosine 3',5'-diphosphate, was saturable and inhibited by bongkrekic acid and other inhibitors of mitochondrial carriers to various degrees. The main physiological role of SLC25A42 is to import CoA into mitochondria in exchange for intramitochondrial (deoxy)adenine nucleotides and adenosine 3',5'-diphosphate. This is the first time that a mitochondrial carrier for CoA and adenosine 3',5'-diphosphate has been characterized biochemically.
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http://dx.doi.org/10.1074/jbc.M109.014118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2709381PMC
July 2009

Identification of mitochondrial carriers in Saccharomyces cerevisiae by transport assay of reconstituted recombinant proteins.

Biochim Biophys Acta 2006 Sep-Oct;1757(9-10):1249-62. Epub 2006 May 23.

Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Via E. Orabona 4, 70125 Bari, Italy.

The inner membranes of mitochondria contain a family of carrier proteins that are responsible for the transport in and out of the mitochondrial matrix of substrates, products, co-factors and biosynthetic precursors that are essential for the function and activities of the organelle. This family of proteins is characterized by containing three tandem homologous sequence repeats of approximately 100 amino acids, each folded into two transmembrane alpha-helices linked by an extensive polar loop. Each repeat contains a characteristic conserved sequence. These features have been used to determine the extent of the family in genome sequences. The genome of Saccharomyces cerevisiae contains 34 members of the family. The identity of five of them was known before the determination of the genome sequence, but the functions of the remaining family members were not. This review describes how the functions of 15 of these previously unknown transport proteins have been determined by a strategy that consists of expressing the genes in Escherichia coli or Saccharomyces cerevisiae, reconstituting the gene products into liposomes and establishing their functions by transport assay. Genetic and biochemical evidence as well as phylogenetic considerations have guided the choice of substrates that were tested in the transport assays. The physiological roles of these carriers have been verified by genetic experiments. Various pieces of evidence point to the functions of six additional members of the family, but these proposals await confirmation by transport assay. The sequences of many of the newly identified yeast carriers have been used to characterize orthologs in other species, and in man five diseases are presently known to be caused by defects in specific mitochondrial carrier genes. The roles of eight yeast mitochondrial carriers remain to be established.
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http://dx.doi.org/10.1016/j.bbabio.2006.05.023DOI Listing
December 2006

Identification of the mitochondrial NAD+ transporter in Saccharomyces cerevisiae.

J Biol Chem 2006 Jan 16;281(3):1524-31. Epub 2005 Nov 16.

Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Via E. Orabona 4, 70125 Bari, Italy.

The mitochondrial carriers are a family of transport proteins that shuttle metabolites, nucleotides, and cofactors across the inner mitochondrial membrane. In Saccharomyces cerevisiae, NAD+ is synthesized outside the mitochondria and must be imported across the permeability barrier of the inner mitochondrial membrane. However, no protein responsible for this transport activity has ever been isolated or identified. In this report, the identification and functional characterization of the mitochondrial NAD+ carrier protein (Ndt1p) is described. The NDT1 gene was overexpressed in bacteria. The purified protein was reconstituted into liposomes, and its transport properties and kinetic parameters were characterized. It transported NAD+ and, to a lesser extent, (d)AMP and (d)GMP but virtually not alpha-NAD+, NADH, NADP+, or NADPH. Transport was saturable with an apparent Km of 0.38 mM for NAD+. The Ndt1p-GFP was found to be targeted to mitochondria. Consistently with Ndt1p localization and its function as a NAD+ transporter, cells lacking NDT1 had reduced levels of NAD+ and NADH in their mitochondria and reduced activity of mitochondrial NAD+-requiring enzymes. Similar results were also found in the mitochondria of cells lacking NDT2 that encodes a protein (Ndt2p) displaying 70% homology with Ndt1p. The delta ndt1 delta ndt2 double mutant exhibited lower mitochondrial NAD+ and NADH levels than the single deletants and a more pronounced delay in growth on nonfermentable carbon sources. The main role of Ndt1p and Ndt2p is to import NAD+ into mitochondria by unidirectional transport or by exchange with intramitochondrially generated (d)AMP and (d)GMP.
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http://dx.doi.org/10.1074/jbc.M510425200DOI Listing
January 2006

Identification of the mitochondrial ATP-Mg/Pi transporter. Bacterial expression, reconstitution, functional characterization, and tissue distribution.

J Biol Chem 2004 Jul 29;279(29):30722-30. Epub 2004 Apr 29.

Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Via Orabona 4, Italy.

The mitochondrial carriers are a family of transport proteins that, with a few exceptions, are found in the inner membranes of mitochondria. They shuttle metabolites, nucleotides, and cofactors through this membrane and thereby connect and/or regulate cytoplasm and matrix functions. ATP-Mg is transported in exchange for phosphate, but no protein has ever been associated with this activity. We have isolated three human cDNAs that encode proteins of 458, 468, and 489 amino acids with 66-75% similarity and with the characteristic features of the mitochondrial carrier family in their C-terminal domains and three EF-hand Ca(2+)-binding motifs in their N-terminal domains. These proteins have been overexpressed in Escherichia coli and reconstituted into phospholipid vesicles. Their transport properties and their targeting to mitochondria demonstrate that they are isoforms of the ATP-Mg/Pi carrier described in the past in whole mitochondria. The tissue specificity of the three isoforms shows that at least one isoform was present in all of the tissues investigated. Because phosphate recycles via the phosphate carrier in mitochondria, the three isoforms of the ATP-Mg/Pi carrier are most likely responsible for the net uptake or efflux of adenine nucleotides into or from the mitochondria and hence for the variation in the matrix adenine nucleotide content, which has been found to change in many physiopathological situations.
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http://dx.doi.org/10.1074/jbc.M400445200DOI Listing
July 2004

Identification of the mitochondrial glutamate transporter. Bacterial expression, reconstitution, functional characterization, and tissue distribution of two human isoforms.

J Biol Chem 2002 May 15;277(22):19289-94. Epub 2002 Mar 15.

Department of Pharmaco-Biology, Laboratory of Biochemistry and Molecular Biology, University of Bari, Via E. Orabona 4, 70125 Bari, Italy.

The mitochondrial carriers are a family of transport proteins in the inner membranes of mitochondria. They shuttle substrates, metabolites, and cofactors through this membrane and connect cytoplasm functions with others in the matrix. Glutamate is co-transported with H(+) (or exchanged for OH(-)), but no protein has ever been associated with this activity. Two human expressed sequence tags encode proteins of 323 and 315 amino acids with 63% identity that are related to the aspartate-glutamate carrier, a member of the carrier family. They have been overexpressed in Escherichia coli and reconstituted into phospholipid vesicles. Their transport properties demonstrate that the two proteins are isoforms of the glutamate/H(+) symporter described in the past in whole mitochondria. Isoform 1 is expressed at higher levels than isoform 2 in all the tissues except in brain, where the two isoforms are expressed at comparable levels. The differences in expression levels and kinetic parameters of the two isoforms suggest that isoform 2 matches the basic requirement of all tissues especially with respect to amino acid degradation, and isoform 1 becomes operative to accommodate higher demands associated with specific metabolic functions such as ureogenesis.
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http://dx.doi.org/10.1074/jbc.M201572200DOI Listing
May 2002