Coenzyme biosynthesis in response to precursor availability reveals incorporation of ß-alanine from pantothenate in prototrophic bacteria.

Coenzymes are important for all classes of enzymatic reactions and essential for cellular metabolism. Most coenzymes are synthesized from dedicated precursors, also referred to as vitamins, which prototrophic bacteria can either produce themselves from simpler substrates or take up from the environment. The extent to which prototrophs use supplied vitamins and whether externally available vitamins affect the size of intracellular coenzyme pools and control endogenous vitamin synthesis is currently largely unknown. Here, we studied coenzyme pool sizes and vitamin incorporation into coenzymes during growth on different carbon sources and vitamin supplementation regimes using metabolomics approaches. We found that the model bacterium Escherichia coli incorporated pyridoxal, niacin, and pantothenate into pyridoxal 5'-phosphate, NAD, and coenzyme A (CoA), respectively. In contrast, riboflavin was not taken up and was produced exclusively endogenously. Coenzyme pools were mostly homeostatic and not affected by externally supplied precursors. Remarkably, we found that pantothenate is not incorporated into CoA as such but is first degraded to pantoate and ß-alanine and then rebuilt. This pattern was conserved in various bacterial isolates, suggesting a preference for ß-alanine over pantothenate utilization in CoA synthesis. Finally, we found that the endogenous synthesis of coenzyme precursors remains active when vitamins are supplied, which is consistent with described expression data of genes for enzymes involved in coenzyme biosynthesis under these conditions. Continued production of endogenous coenzymes may ensure rapid synthesis of the mature coenzyme under changing environmental conditions, protect against coenzyme limitation, and explain vitamin availability in naturally oligotrophic environments.

Overexpression of Human Mutant PANK2 Proteins Affects Development and Motor Behavior of Zebrafish Embryos.

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is a genetic and early-onset neurodegenerative disorder characterized by iron accumulation in the basal ganglia. It is due to mutations in Pantothenate Kinase 2 (PANK2), an enzyme that catalyzes the phosphorylation of vitamin B5, first and essential step in coenzyme A (CoA) biosynthesis. Most likely, an unbalance of the neuronal levels of this important cofactor represents the initial trigger of the neurodegenerative process, yet a complete understanding of the connection between PANK2 malfunctioning and neuronal death is lacking. Most PKAN patients carry mutations in both alleles and a loss of function mechanism is proposed to explain the pathology. When PANK2 mutants were analyzed for stability, dimerization capacity, and enzymatic activity in vitro, many of them showed properties like the wild-type form. To further explore this aspect, we overexpressed the wild-type protein, two mutant forms with reduced kinase activity and two retaining the catalytic activity in zebrafish embryos and analyzed the morpho-functional consequences. While the wild-type protein had no effects, all mutant proteins generated phenotypes that partially resembled those observed in pank2 and coasy morphants and were rescued by CoA and vitamin B5 supplementation. The overexpression of PANK2 mutant forms appears to be associated with perturbation in CoA availability, irrespective of their catalytic activity.

Pantothenic acid biosynthesis in the parasite Toxoplasma gondii: a target for chemotherapy.

Toxoplasma gondii is a major food pathogen and neglected parasitic infection that causes eye disease, birth defects, and fetal abortion and plays a role as an opportunistic infection in AIDS. In this study, we investigated pantothenic acid (vitamin B5) biosynthesis in T. gondii. Genes encoding the full repertoire of enzymes for pantothenate synthesis and subsequent metabolism to coenzyme A were identified and are expressed in T. gondii. A panel of inhibitors developed to target Mycobacterium tuberculosis pantothenate synthetase were tested and found to exhibit a range of values for inhibition of T. gondii growth. Two inhibitors exhibited lower effective concentrations than the currently used toxoplasmosis drug pyrimethamine. The inhibition was specific for the pantothenate pathway, as the effect of the pantothenate synthetase inhibitors was abrogated by supplementation with pantothenate. Hence, T. gondii encodes and expresses the enzymes for pantothenate synthesis, and this pathway is essential for parasite growth. These promising findings increase our understanding of growth and metabolism in this important parasite and highlight pantothenate synthetase as a new drug target.

Metabolic consequences of mitochondrial coenzyme A deficiency in patients with PANK2 mutations.

Pantothenate kinase-associated neurodegeneration (PKAN) is a rare, inborn error of metabolism characterized by iron accumulation in the basal ganglia and by the presence of dystonia, dysarthria, and retinal degeneration. Mutations in pantothenate kinase 2 (PANK2), the rate-limiting enzyme in mitochondrial coenzyme A biosynthesis, represent the most common genetic cause of this disorder. How mutations in this core metabolic enzyme give rise to such a broad clinical spectrum of pathology remains a mystery. To systematically explore its pathogenesis, we performed global metabolic profiling on plasma from a cohort of 14 genetically defined patients and 18 controls. Notably, lactate is elevated in PKAN patients, suggesting dysfunctional mitochondrial metabolism. As predicted, but never previously reported, pantothenate levels are higher in patients with premature stop mutations in PANK2. Global metabolic profiling and follow-up studies in patient-derived fibroblasts also reveal defects in bile acid conjugation and lipid metabolism, pathways that require coenzyme A. These findings raise a novel therapeutic hypothesis, namely, that dietary fats and bile acid supplements may hold potential as disease-modifying interventions. Our study illustrates the value of metabolic profiling as a tool for systematically exploring the biochemical basis of inherited metabolic diseases.

Stable isotope labeling by essential nutrients in cell culture for preparation of labeled coenzyme A and its thioesters.

Stable isotope dilution mass spectrometry (MS) represents the gold standard for quantification of endogenously formed cellular metabolites. Although coenzyme A (CoA) and acyl-CoA thioester derivatives are central players in numerous metabolic pathways, the lack of a commercially available isotopically labeled CoA limits the development of rigorous MS-based methods. In this study, we adapted stable isotope labeling by amino acids in cell culture (SILAC) methodology to biosynthetically generate stable isotope labeled CoA and thioester analogues for use as internal standards in liquid chromatography/multiple reaction monitoring mass spectrometry (LC/MRM-MS) assays. This was accomplished by incubating murine hepatocytes (Hepa 1c1c7) in media in which pantothenate (a precursor of CoA) was replaced with [(13)C(3)(15)N(1)]-pantothenate. Efficient incorporation into various CoA species was optimized to >99% [(13)C(3)(15)N(1)]-pantothenate after three passages of the murine cells in culture. Charcoal-dextran-stripped fetal bovine serum (FBS) was found to be more efficient for serum supplementation than dialyzed or undialyzed FBS, due to lower contaminating unlabeled pantothenate content. Stable isotope labeled CoA species were extracted and utilized as internal standards for CoA thioester analysis in cell culture models. This methodology of stable isotope labeling by essential nutrients in cell culture (SILEC) can serve as a paradigm for using vitamins and other essential nutrients to generate stable isotope standards that cannot be readily synthesized.

Current medical aspects of pantethine.

Pantethine, the stable disulfide form of pantetheine, is the major precursor of coenzyme A, which plays a central role in the metabolism of lipids and carbohydrates. Coenzyme A is a cofactor in over 70 enzymatic pathways, including fatty acid oxidation, carbohydrate metabolism, pyruvate degradation, amino acid catabolism, haem synthesis, acetylcholine synthesis, phase II detoxification, acetylation, etc. Pantethine has beneficial effects in vascular disease, it able to decrease the hyperlipidaemia, moderate the platelet function and prevent the lipid-peroxidation. Moreover its neuro-endocrinological regulating role, its good influence on cataract and cystinosis are also proved. This molecule is a well-tolerated therapeutic agent; the frequency of its side-effect is very low and mild. Based on these preclinical and clinical data, it could be recommended using this compound as adjuvant therapy.

Influence of the plant extract complex "AdMax" on global gene expression levels in cultured human fibroblasts.

Ethanol/water extracts from roots of Leuzea carthamoides Iljin, Rhodiola rosea L., Eleutherococcus senticosus Maxim, and from dry berries of Schizandra chinensis Baill. are known as adaptogenic remedies, which enhance physical endurance, counteract fatigue and restore suppressed immunity. Molecular mechanisms underlying effects of the extracts are poorly understood. In this study, a combination of these four extracts called AdMax™ (Nulab, Inc., Florida) was examined for its ability to influence gene expression levels in cultured human fibroblasts in vitro with the help of whole-genome Affymetrix oligonucleotide microarrays. We showed that AdMax treatment results in significant changes (at least 2 fold, p <. 05) in expression of 67 genes that are involved in metabolism of protein, nucleic acids, lipid and carbohydrates, in regulation of transcription, protein and ion transport, response to stimulus and stress. Enhancing expression of the PANK2 gene is of special interest in connection with AdMax ability to enhance physical endurance and counteract fatigue. PANK2 encodes a mitochondrial enzyme pantothenate kinase 2, which provides coenzyme A biosynthesis and thereby plays crucial role in energy metabolism. Partial deficiency of PANK2 gene activity leads to pantothenate kinase-associated neurodegeneration. In this connection potential therapeutic use of AdMax in patients with neurodegenerative diseases is discussed.

Plant coenzyme A biosynthesis: characterization of two pantothenate kinases from Arabidopsis.

In bacterial and animal coenzyme A (CoA) biosynthesis, pantothenate kinase (PANK) activity is critical in regulating intracellular CoA levels. Less is known about the role of PANK in plants, although a single plant isozyme from Arabidopsis, AtPANK1, was previously cloned and analyzed in vitro. We report here the characterization of a second pantothenate kinase of Arabidopsis, AtPANK2, as well as characterization of the physiological roles of both plant enzymes. The activity of the second pantothenate kinase, AtPANK2, was confirmed by its ability to complement the temperature-sensitive mutation of the bacterial pantothenate kinase in E. coli strain ts9. Knock-out mutation of either AtPANK1 or AtPANK2 did not inhibit plant growth, whereas pank1-1/pank2-1 double knockout mutations were embryo lethal. The phenotypes of the mutant plants demonstrated that only one of the AtPANK enzymes is necessary and sufficient for producing adequate CoA levels, and that no other enzyme can compensate for the loss of both isoforms. Real-time PCR measurements of AtPANK1 and AtPANK2 transcripts indicated that both enzymes are expressed with similar patterns in all tissues examined, further suggesting that AtPANK1 and AtPANK2 have complementary roles. The two enzymes have homologous pantothenate kinase domains, but AtPANK2 also carries a large C-terminal protein domain. Sequence comparisons indicate that this type of "bifunctional" pantothenate kinase is conserved in other higher eukaryotes as well. Although the function of the C-terminal domain is not known, homology structure modeling suggests it contains a highly conserved cluster of charged residues that likely constitute a metal-binding site.

Mammalian cysteine metabolism: new insights into regulation of cysteine metabolism.

The mammalian liver tightly regulates its free cysteine pool, and intracellular cysteine in rat liver is maintained between 20 and 100 nmol/g even when sulfur amino acid intakes are deficient or excessive. By keeping cysteine levels within a narrow range and by regulating the synthesis of glutathione, which serves as a reservoir of cysteine, the liver addresses both the need to have adequate cysteine to support normal metabolism and the need to keep cysteine levels below the threshold of toxicity. Cysteine catabolism is tightly regulated via regulation of cysteine dioxygenase (CDO) levels in the liver, with the turnover of CDO protein being dramatically decreased when intracellular cysteine levels increase. This occurs in response to changes in the intracellular cysteine concentration via changes in the rate of CDO ubiquitination and degradation. Glutathione synthesis also increases when intracellular cysteine levels increase as a result of increased saturation of glutamate-cysteine ligase (GCL) with cysteine, and this contributes to removal of excess cysteine. When cysteine levels drop, GCL activity increases, and the increased capacity for glutathione synthesis facilitates conservation of cysteine in the form of glutathione (although the absolute rate of glutathione synthesis still decreases because of the lack of substrate). This increase in GCL activity is dependent on up-regulation of expression of both the catalytic and modifier subunits of GCL, resulting in an increase in total catalytic subunit plus an increase in the catalytic efficiency of the enzyme. An important role of cysteine utilization for coenzyme A synthesis in maintaining cellular cysteine levels in some tissues, and a possible connection between the necessity of controlling cellular cysteine levels to regulate the rate of hydrogen sulfide production, have been suggested by recent literature and are areas that deserve further study.

4'-phosphopantetheine and coenzyme A biosynthesis in plants.

Coenzyme A is required for many synthetic and degradative reactions in intermediary metabolism and is the principal acyl carrier in prokaryotic and eukaryotic cells. Coenzyme A is synthesized in five steps from pantothenate, and recently the CoaA biosynthetic genes in bacteria and human have all been identified and characterized. Coenzyme A biosynthesis in plants is not fully understood, and to date only the AtHAL3a (AtCoaC) gene of Arabidopsis thaliana has been cloned and identified as 4'-phosphopantothenoylcysteine (PPC) decarboxylase (Kupke, T., Hernández-Acosta, P., Steinbacher, S., and Culiáñez-Macià, F. A. (2001) J. Biol. Chem. 276, 19190-19196). Here, we demonstrate the cloning of the four missing genes, purification of the enzymes, and identification of their functions. In contrast to bacterial PPC synthetases, the plant synthetase is not CTP-but ATP-dependent. The complete biosynthetic pathway from pantothenate to coenzyme A was reconstituted in vitro by adding the enzymes pantothenate kinase (AtCoaA), 4'-phosphopantothenoylcysteine synthetase (AtCoaB), 4'-phosphopantothenoylcysteine decarboxylase (AtCoaC), 4'-phosphopantetheine adenylyltransferase (AtCoaD), and dephospho-coenzyme A kinase (AtCoaE) to a mixture containing pantothenate, cysteine, ATP, dithiothreitol, and Mg2+.

Complete reconstitution of the human coenzyme A biosynthetic pathway via comparative genomics.

The biosynthesis of CoA from pantothenic acid (vitamin B5) is an essential universal pathway in prokaryotes and eukaryotes. The CoA biosynthetic genes in bacteria have all recently been identified, but their counterparts in humans and other eukaryotes remained mostly unknown. Using comparative genomics, we have identified human genes encoding the last four enzymatic steps in CoA biosynthesis: phosphopantothenoylcysteine synthetase (EC ), phosphopantothenoylcysteine decarboxylase (EC ), phosphopantetheine adenylyltransferase (EC ), and dephospho-CoA kinase (EC ). Biological functions of these human genes were verified using a complementation system in Escherichia coli based on transposon mutagenesis. The individual human enzymes were overexpressed in E. coli and purified, and the corresponding activities were experimentally verified. In addition, the entire pathway from phosphopantothenate to CoA was successfully reconstituted in vitro using a mixture of purified recombinant enzymes. Human recombinant bifunctional phosphopantetheine adenylyltransferase/dephospho-CoA kinase was kinetically characterized. This enzyme was previously suggested as a point of CoA biosynthesis regulation, and we have observed significant differences in mRNA levels of the corresponding human gene in normal and tumor cells by Northern blot analysis.

Biosynthesis and degradation both contribute to the regulation of coenzyme A content in Escherichia coli.

Escherichia coli mutants [coaA16(Fr); Fr indicates feedback resistance] were isolated which possessed a pantothenate kinase activity that was refractory to feedback inhibition by coenzyme A (CoA). Strains harboring this mutation had CoA levels that were significantly elevated compared with strains containing the wild-type kinase and also overproduced both intra- and extracellular 4'-phosphopantetheine. The origin of 4'-phosphopantetheine was investigated by using strain SJ135 [panD delta(aroP-aceEF)], in which synthesis of acetyl-CoA was dependent on the addition of an acetate growth supplement. Rapid degradation of CoA to 4'-phosphopantetheine was triggered by the conversion of acetyl-CoA to CoA following the removal of acetate from the media. CoA hydrolysis under these conditions appeared not to involve acyl carrier protein prosthetic group turnover since [acyl carrier protein] phosphodiesterase was inhibited equally well by acetyl-CoA or CoA. These data support the view that the total cellular CoA content is controlled by modulation of biosynthesis at the pantothenate kinase step and by degradation of CoA to 4'-phosphopantetheine.

[Antitoxic properties of pantothenic acid derivatives, precursors of coenzyme A biosynthesis, with regard to kanamycin]. / Antitoksicheskie svoistva proizvodnykh pantotenovoi kisloty, predshestvennikov biosinteza kofermenta A v otnoshenii kanamitsina.

The effect of calcium pantothenate (CPN)B 4'-phospho-CPN (PCP), pantetheine (PT) and calcium S-sulfopantetheine (SPN) on acute toxicity of kanamycin sulfate was studied on albino mice. The above derivatives of pantothenic acid except PT lowered the antibiotic toxicity. The coefficient of the antitoxic effect (LD50/ED50) of SPN and PCP was 1.3-1.4 times higher than that of CPN. The combined use of kanamycin (1/5 of the LD50) with CPN, PCP or PT (30 mg/kg bw was equivalent to CPN) for 15 days prevented the increase in the total content of CoA and in the content of the fraction of free CoA and the precursors of its biosynthesis participating in the reaction of N-acetylation in the liver and brain. The contents of these substances were within the normal during the whole experiment. A certain increase in the activity of pantothenate kinase in the liver cytosol due to the use of kanamycin was eliminated by the simultaneous use of PCP and PT. The vitamin-containing compounds PCP and SPN were recommended for the clinical trials as agents preventing complications of kanamycin therapy.

Differential effects of cysteine on protein and coenzyme A synthesis in rat heart.

The effect of cysteine availability on protein and coenzyme A (CoA) synthesis in perfused rat heart was incompletely evaluated in earlier experiments because rapid conversion of cysteine to cystine occurred when the perfusion buffer was oxygenated. This conversion was minimized by addition of an excess of reducing agents such as dithiothreitol or mercaptodextran or by provision of bathocuproine disulfonate, a copper chelator. Dithiothreitol was not a suitable protective agent because it reduced ATP and creatine phosphate contents. Perfusion of hearts with [35S]cystine or [35S]cysteine in the presence of mercaptodextran resulted in a 22-fold or 5-fold increase, respectively, in incorporation of [35S] into protein and a 5-fold or 8-fold increase, respectively, in incorporation into CoA compared with hearts supplied [35S]cystine or [35S]cysteine without the reducing agent. When compared with hearts perfused at an aortic pressure of 90 mmHg with bicarbonate buffer that contained 15 mM glucose, 25 mU insulin/ml, 0.4 mM [14C]phenylalanine, no cysteine and plasma levels of other amino acids, provision of 0.09 or 0.2 mM cysteine alone or in the presence of mercaptodextran, or bathocuproine disulfonate enhanced rates of protein synthesis 16-35%. When 0.2 mM cysteine was added to bicarbonate buffer containing 7 microM pantothenic acid, supplementation with mercaptodextran or bathocuproine disulfonate was required to raise CoA content. These results indicated that an exogenous supply of cysteine was needed to maintain maximal rates of protein and CoA synthesis in the perfused rat heart. Protective compounds were required to obtain the cysteine effect on CoA but not on protein synthesis.