The mitochondrial phosphate carrier: Role in oxidative metabolism, calcium handling and mitochondrial disease (original) (raw)
Related papers
Mitochondrial Phosphate–Carrier Deficiency: A Novel Disorder of Oxidative Phosphorylation
The American Journal of Human Genetics, 2007
The mitochondrial phosphate carrier SLC25A3 transports inorganic phosphate into the mitochondrial matrix, which is essential for the aerobic synthesis of adenosine triphosphate (ATP). We identified a homozygous mutation-c.215GrA (p.Gly72Glu)-in the alternatively spliced exon 3A of this enzyme in two siblings with lactic acidosis, hypertrophic cardiomyopathy, and muscular hypotonia who died within the 1st year of life. Functional investigation of intact mitochondria showed a deficiency of ATP synthesis in muscle but not in fibroblasts, which correlated with the tissuespecific expression of exon 3A in muscle versus exon 3B in fibroblasts. The enzyme defect was confirmed by complementation analysis in yeast. This is the first report of patients with mitochondrial phosphate-carrier deficiency.
Cell Death & Differentiation, 2014
The mitochondrial phosphate carrier (PiC) is critical for ATP synthesis by serving as the primary means for mitochondrial phosphate import across the inner membrane. In addition to its role in energy production, PiC is hypothesized to have a role in cell death as either a component or a regulator of the mitochondrial permeability transition pore (MPTP) complex. Here, we have generated a mouse model with inducible and cardiac-specific deletion of the Slc25a3 gene (PiC protein). Loss of PiC protein did not prevent MPTP opening, suggesting it is not a direct pore-forming component of this complex. However, Slc25a3 deletion in the heart blunted MPTP opening in response to Ca 2 þ challenge and led to a greater Ca 2 þ uptake capacity. This desensitization of MPTP opening due to loss or reduction in PiC protein attenuated cardiac ischemic-reperfusion injury, as well as partially protected cells in culture from Ca 2 þ overload induced death. Intriguingly, deletion of the Slc25a3 gene from the heart long-term resulted in profound hypertrophy with ventricular dilation and depressed cardiac function, all features that reflect the cardiomyopathy observed in humans with mutations in SLC25A3. Together, these results demonstrate that although the PiC is not a direct component of the MPTP, it can regulate its activity, suggesting a novel therapeutic target for reducing necrotic cell death. In addition, mice lacking Slc25a3 in the heart serve as a novel model of metabolic, mitochondrial-driven cardiomyopathy.
Phosphate transport in mitochondria: Past accomplishments, present problems, and future challenges
Journal of Bioenergetics and Biomembranes, 1993
The requirement of inorganic phosphate (Pi) for oxidative phosphorylation in eukaryotic cells is fulfilled through specific Pi transport systems. The mitochondrial proton/phosphate symporter (Pi c) is a membrane-embedded protein which translocates Pi from the cytosol into the mitochondrial matrix. Pi c is responsible for the very rapid transport of most of the Pi used in ATP synthesis. During the past five years there have been advances on several fronts. Genomic and cDNA clones for yeast, bovine, rat, and human Pi c have been isolated and sequenced. Functional expression of yeast Pi c in yeast strains deficient in Pi transport and expression in Eseherichia coli of a chimera protein involving Pi c and ATP synthase c~ subunit have been accomplished. Pi c, in contrast to other members of the family of transporters involved in energy metabolism, was demonstrated to have a presequence, which optimizes the import of the precursor protein into mitochondria. Six transmembrane segments appear to be a structural feature shared between Pic and other mitochondrial anion carriers, and recent-site directed mutagenesis studies implicate structure-functional relationships to bacteriorhodopsin. These recent advances on Pic will be assessed in light of a more global interpretation of transport mechanism across the inner mitochondrial membrane.
Diseases Caused by Mutations in Mitochondrial Carrier Genes SLC25: A Review
Biomolecules, 2020
In the 1980s, after the mitochondrial DNA (mtDNA) had been sequenced, several diseases resulting from mtDNA mutations emerged. Later, numerous disorders caused by mutations in the nuclear genes encoding mitochondrial proteins were found. A group of these diseases are due to defects of mitochondrial carriers, a family of proteins named solute carrier family 25 (SLC25), that transport a variety of solutes such as the reagents of ATP synthase (ATP, ADP, and phosphate), tricarboxylic acid cycle intermediates, cofactors, amino acids, and carnitine esters of fatty acids. The disease-causing mutations disclosed in mitochondrial carriers range from point mutations, which are often localized in the substrate translocation pore of the carrier, to large deletions and insertions. The biochemical consequences of deficient transport are the compartmentalized accumulation of the substrates and dysfunctional mitochondrial and cellular metabolism, which frequently develop into various forms of myopathy, encephalopathy, or neuropathy. Examples of diseases, due to mitochondrial carrier mutations are: combined D-2-and L-2-hydroxyglutaric aciduria, carnitine-acylcarnitine carrier deficiency, hyperornithinemia-hyperammonemia-homocitrillinuria (HHH) syndrome, early infantile epileptic encephalopathy type 3, Amish microcephaly, aspartate/glutamate isoform 1 deficiency, congenital sideroblastic anemia, Fontaine progeroid syndrome, and citrullinemia type II. Here, we review all the mitochondrial carrier-related diseases known until now, focusing on the connections between the molecular basis, altered metabolism, and phenotypes of these inherited disorders.
Mitochondrial Transporters as Novel Targets for Intracellular Calcium Signaling
Physiological Reviews, 2007
transition in rat liver mitochondria is modulated by the ATP-Mg/Pi carrier. Am J Physiol Gastrointest Liver Physiol 285: G274-G281, 2003; 10.1152 10. /ajpgi.00052.2003 permeability transition, due to opening of the permeability transition pore (PTP), is triggered by Ca 2ϩ in conjunction with an inducing agent such as phosphate. However, incubation of rat liver mitochondria in the presence of low micromolar concentrations of Ca 2ϩ and millimolar concentrations of phosphate is known to also cause net efflux of matrix adenine nucleotides via the ATP-Mg/Pi carrier. This raises the possibility that adenine nucleotide depletion through this mechanism contributes to mitochondrial permeability transition. Results of this study show that phosphateinduced opening of the mitochondrial PTP is, at least in part, secondary to depletion of the intramitochondrial adenine nucleotide content via the ATP-Mg/Pi carrier. Delaying net adenine nucleotide efflux from mitochondria also delays the onset of phosphate-induced PTP opening. Moreover, mitochondria that are depleted of matrix adenine nucleotides via the ATP-Mg/Pi carrier show highly increased susceptibility to swelling induced by high Ca 2ϩ concentration, atractyloside, and the prooxidant tert-butylhydroperoxide. Thus the ATP-Mg/Pi carrier, by regulating the matrix adenine nucleotide content, can modulate the sensitivity of rat liver mitochondria to undergo permeability transition. This has important implications for hepatocytes under cellular conditions in which the intramitochondrial adenine nucleotide pool size is depleted, such as in hypoxia or ischemia, or during reperfusion when the mitochondria are exposed to increased oxidative stress.
Journal of Biological Chemistry, 2009
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 3,5diphosphate. This is the first time that a mitochondrial carrier for CoA and adenosine 3,5-diphosphate has been characterized biochemically. . The abbreviations used are: SLC25, solute carrier family 25; GFP, green fluorescent protein; BFP, blue fluorescent protein; CHO, Chinese hamster ovary; CoA, coenzyme A; EG(B)FP, enhanced green (blue) fluorescence protein; PAP, adenosine 3Ј,5Ј-diphosphate.
Nature medicine, 1999
In recent years, genetic defects of the mitochondrial genome (mtDNA) were shown to be associated with a heterogeneous group of disorders, known as mitochondrial diseases 1,2 , but the cellular events deriving from the molecular lesions and the mechanistic basis of the specificity of the syndromes are still incompletely understood. Mitochondrial calcium (Ca 2+ ) homeostasis depends on close contacts with the endoplasmic reticulum 3 and is essential in modulating organelle function 4-6 . Given the strong dependence of mitochondrial Ca 2+ uptake on the membrane potential and the intracellular distribution of the organelle, both of which may be altered in mitochondrial diseases, we investigated the occurrence of defects in mitochondrial Ca 2+ handling in living cells with either the tRNA Lys mutation of MERRF (myoclonic epilepsy with ragged-red fibers) 7-9 or the ATPase mutation of NARP (neurogenic muscle weakness, ataxia and retinitis pigmentosa) 10-13 . There was a derangement of mitochondrial Ca 2+ homeostasis in MERRF, but not in NARP cells, whereas cytosolic Ca 2+ responses were normal in both cell types. Treatment of MERRF cells with drugs affecting organellar Ca 2+ transport mostly restored both the agonist-dependent mitochondrial Ca 2+ uptake and the ensuing stimulation of ATP production. These results emphasize the differences in the cellular pathogenesis of the various mtDNA defects and indicate specific pharmacological approaches to the treatment of some mitochondrial diseases.
Biomolecules
Subcellular compartmentation is a fundamental property of eukaryotic cells. Communication and metabolic and regulatory interconnectivity between organelles require that solutes can be transported across their surrounding membranes. Indeed, in mammals, there are hundreds of genes encoding solute carriers (SLCs) which mediate the selective transport of molecules such as nucleotides, amino acids, and sugars across biological membranes. Research over many years has identified the localization and preferred substrates of a large variety of SLCs. Of particular interest has been the SLC25 family, which includes carriers embedded in the inner membrane of mitochondria to secure the supply of these organelles with major metabolic intermediates and coenzymes. The substrate specificity of many of these carriers has been established in the past. However, the route by which animal mitochondria are supplied with NAD+ had long remained obscure. Only just recently, the existence of a human mitochond...
Biogenesis of the mitochondrial phosphate carrier
European Journal of Biochemistry, 1991
The mitochondrial phosphate carrier (Pic) is a member of the family of inner-membrane carrier proteins which are generally synthesized without a cleavable presequence. Surprisingly, the cDNA sequences of bovine and rat P i c suggested the existence of an amino-terminal extension sequence in the precursor of Pic. By expressing P i c in vitro, we found that PIC is indeed synthesized as a larger precursor. This precursor was imported and proteolytically processed by mitochondria, whereby the correct amino-terminus of the mature protein was generated. Import of P i c showed the characteristics of mitochondrial protein uptake, such as dependence on ATP and a membrane potential and involvement of contact sites between mitochondrial outer and inner membranes. The precursor imported in vitro was correctly assembled into the functional form, demonstrating that the authentic import and assembly pathway of P i c was reconstituted when starting with the presequence-carrying precursor. These results are discussed in connection with the recently postulated role of P i c as an import receptor located in the outer membrane.
Molecular Biology of the Cell, 2014
Emerging findings suggest that two lineages of mitochondrial Ca 2+ uptake participate during active and resting states: 1) the major eukaryotic membrane potential-dependent mitochondrial Ca 2+ uniporter and 2) the evolutionarily conserved exchangers and solute carriers, which are also involved in ion transport. Although the influx of Ca 2+ across the inner mitochondrial membrane maintains metabolic functions and cell death signal transduction, the mechanisms that regulate mitochondrial Ca 2+ accumulation are unclear. Solute carrierssolute carrier 25A23 (SLC25A23), SLC25A24, and SLC25A25-represent a family of EF-handcontaining mitochondrial proteins that transport Mg-ATP/Pi across the inner membrane. RNA interference-mediated knockdown of SLC25A23 but not SLC25A24 and SLC25A25 decreases mitochondrial Ca 2+ uptake and reduces cytosolic Ca 2+ clearance after histamine stimulation.