bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucose transport and glucose transporter GLUT4 are regulated by product(s) of intermediary metabolism in cardiomyocytes
Authors: FISCHER Yvan , BÖTTCHER Uwe , EBLENKAMP Markus , THOMAS Julia , JÜNGLING Eberhard , RÖSEN Peter , KAMMERMEIER Helmut
Published: August 2015

Alternative substrates of energy metabolism are thought to contribute to the impairment of heart and muscle glucose utilization in insulin-resistant states. We have investigated the acute effects of substrates in isolated rat cardiomyocytes. Exposure to lactate, pyruvate, propionate, acetate, palmitate, β-hydroxybutyrate or α-oxoglutarate led to the depression of glucose transport by up to 50%, with lactate, pyruvate and propionate being the most potent agents. The percentage inhibition was greater in cardiomyocytes in which glucose transport was stimulated with the α-adrenergic agonist phenylephrine or with a submaximal insulin concentration than in basal or fully insulin-stimulated cells. Cardiomyocytes from fasted or diabetic rats displayed a similar sensitivity to substrates as did cells from control animals. On the other hand, the amination product of pyruvate (alanine), as well as valine and the aminotransferase inhibitors cycloserine and amino-oxyacetate, stimulated glucose transport about 2-fold. In addition, the effect of pyruvate was counteracted by cycloserine. Since reversible transamination reactions are known to affect the pool size of the citrate cycle, the influence of substrates, amino acids and aminotransferase inhibitors on citrate, malate and glutamate content was examined. A significant negative correlation was found between alterations in glucose transport and the levels of citrate (P < 0.01) or malate (P < 0.01), and there was a positive correlation between glucose transport and glutamate levels (P < 0.05). In contrast, there was no correlation with changes in [1-14C]pyruvate oxidation or in glucose-6-phosphate levels. Finally, pyruvate decreased the abundance of GLUT4 glucose transporters at the surface of phenylephrine- or insulin-stimulated cells by 34% and 27% respectively, as determined by using the selective photoaffinity label [3H]ATB-BMPA {[3H]2-N-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]-1,3-bis-(d-mannos-4-yloxy)propyl-2-amine}. In conclusion, cardiomyocyte glucose transport is subject to counter-regulation by alternative substrates. The glucose transport system appears to be controlled by (a) compound(s) of intermediary metabolism (other than glucose 6-phosphate), but in a different way than pyruvate dehydrogenase. Transport inhibition eventually occurs via a decrease in the amount of glucose transporters in the plasma membrane.
Electrical stimulation of C2C12 myotubes induces contractions and represses thyroid-hormone-dependent transcription of the fast-type sarcoplasmic-reticulum Ca2+-ATPase gene
Authors: THELEN Marc H. M. , SIMONIDES Warner S. , HARDEVELD Cornelis van
Published: August 2015

Chronic low-frequency contraction of skeletal muscle, either induced by a slow motor nerve or through direct electrical stimulation, generally induces expression of proteins associated with the slow phenotype, while repressing the corresponding fast isoforms. Contractions thereby counteract the primarily transcriptional effect of thyroid hormone (T3), which results in the selective induction and stimulation of expression of fast isoforms. We studied the regulation of expression of the fast-type sarcoplasmic-reticulum Ca2+-ATPase (SERCA1), a characteristic component of the fast phenotype. Previous work suggested that reduction of SERCA1 expression by contractile activity might result from interference with the T3-dependent transcriptional stimulation of the SERCA1 gene. The present study was set up to test this unexpected mode of action of contractile activity. We show that electrical stimulation of C2C12 mouse myotubes, which results in synchronous contractions at the imposed frequency, reduces basal but virtually abolishes T3-dependent SERCA1 expression. T3-dependent expression of a reporter gene driven by the SERCA1 promoter was similarly affected by electrical stimulation. This is the first demonstration that the counteracting effects on muscle gene expression of electrically induced contractions and T3 may interact at the transcriptional level.
Molecular cloning and biochemical characterization of a Drosophila phosphatidylinositol-specific phosphoinositide 3-kinase
Authors: LINASSIER Claude , MacDOUGALL Lindsay K. , DOMIN Jan , WATERFIELD Michael D.
Published: August 2015

Molecular, biochemical and genetic characterization of phosphoinositide 3-kinases (PI3Ks) have identified distinct classes of enzymes involved in processes mediated by activation of cell-surface receptors and in constitutive intracellular protein trafficking events. The latter process appears to involve a PtdIns-specific PI3K first described in yeast as a mutant, vps34, defective in the sorting of newly synthesized proteins from the Golgi to the vacuole. We have identified a representative member of each class of PI3Ks in Drosophila using a PCR-based approach. In the present paper we describe the molecular cloning of a PI3K from Drosophila, PI3KŐ59F, that shows sequence similarity to Vps34. PI3KŐ59F encodes a protein of 108 kDa co-linear with Vps34 homologues, and with three regions of sequence similarity to other PI3Ks. Biochemical characterization of the enzyme, by expression of the complete coding sequence as a glutathione S-transferase fusion protein in Sf9 cells, demonstrates that PI3KŐ59F is a PtdIns-specific PI3K that can utilize either Mg2+ or Mn2+. This activity is sensitive to inhibition both by non-ionic detergent (Nonidet P40) and by wortmannin (IC50 10 nM). PI3KŐ59F, therefore, conserves both the structural and biochemical properties of the Vps34 class of enzymes.
Utilization of troponin C as a model calcium-binding protein for mapping of the calmodulin-binding sites of caldesmon
Authors: POLYAKOV Alexei A. , GUSEV Nikolai B.
Published: August 2015

Troponin C, a structural analogue of calmodulin, was used for mapping the calmodulin-binding sites of caldesmon. The apparent Kd values for the formation of the caldesmonŐcalcium-binding-protein complex as determined by native gel electrophoresis were 0.5, 1.2 and 3.9 ƁM for calmodulin, rabbit skeletal muscle troponin C and bovine cardiac troponin C respectively. Troponin C induced a 4Ő6 nm blue shift of the Trp fluorescence of caldesmon without affecting the amplitude of fluorescence. In the presence of Ca2+, troponin C induced partial displacement of caldesmon from actinŐtropomyosin complexes. Addition of 5,5ƀ-dithiobis(nitrobenzoic) acid to an equimolar complex of caldesmon and troponin C induced disulphide cross-linking between Cys-98 of rabbit skeletal muscle troponin C and the single Cys residue of duck gizzard caldesmon, located in a position analogous to Cys-580 of the chicken gizzard protein. The cross-linked caldesmonŐtroponin C complex was ineffective in inhibiting actomyosin ATPase activity. It is concluded that Cys-580 of caldesmon can be located close to both the central helix of calcium-binding proteins and the C-terminal domain of actin. This may be important for the regulation of actomyosin ATPase activity by caldesmon.
Diphospho-myo-inositol phosphates from Dictyostelium identified as d-6-diphospho-myo-inositol pentakisphosphate and d-5,6-bisdiphospho-myo-inositol tetrakisphosphate
Authors: LAUSSMANN Tim , REDDY Komandla Malla , REDDY K. Kishta , FALCK J. R. , VOGEL Günter
Published: August 2015

Two diphospho-myo-inositol phosphates from Dictyostelium were recently investigated by two-dimensional 1H/31P NMR analysis and assigned to be either d-4-diphospho-myo-inositol pentakisphosphate (d-4-PP-InsP5) and d-4,5-bisdiphospho-myo-inositol tetrakisphosphate (d-4,5-bis-PP-InsP4) or their corresponding enantiomers d-6-PP-InsP5 and d-5,6-bis-PP-InsP4. In the present study the naturally occurring enantiomers were identified by using defined synthetic PP-InsP5 isomers as substrates for a partially purified PP-InsP5 5-kinase from Dictyostelium. This enzyme specifically phosphorylates the naturally occurring PP-InsP5 and the synthetic d-6-PP-InsP5, leading to d-5,6-bis-PP-InsP4. In contrast, neither d-4-PP-InsP5 nor d-1-PP-InsP5 or d-3-PP-InsP5 are converted by the enzyme.
Identification of a putative flexible loop in Arabidopsis glutathione synthetase
Authors: WANG Chang-Lin , OLIVER David J.
Published: August 2015

Glutathione synthetase catalyses the ATP-dependent ligation of γ-glutamylcysteine with glycine to form glutathione. Amino acid sequence comparisons between the Arabidopsis and the Escherichia coli proteins suggested that a region, identified as a small flexible loop that covers the active site of the E. coli protein, might be conserved in the eukaryotic protein. Three site-directed mutations in the Arabidopsis protein were generated to test this hypothesis. Two mutations within the conserved region (Lys367/Pro368 → Asn/Ser and Gly374 → Val) inactivated the enzyme in an in vivo assay based on cadmium resistance in S. pombe, and in an in vitro assay of the activity of the enzyme expressed in E. coli. A third mutation outside of this conserved region (Leu363 → Glu) had a smaller effect in both assays. These results are consistent with the idea that this glycine-rich loop in the Arabidopsis and E. coli proteins might serve the same function in covering the active site of the enzyme.
Regulation of the rat cardiac troponin I gene by the transcription factor GATA-4
Authors: MURPHY Anne M. , THOMPSON W. Reid , PENG Ling Fan , JONES Lawrence
Published: August 2015

Troponin I is a thin-filament contractile protein expressed in striated muscle. There are three known troponin I genes which are expressed in a muscle-fibre-type-specific manner in mature animals. Although the slow skeletal troponin I isoform is expressed in fetal and neonatal heart, the cardiac isoform is restricted in its expression to the myocardium at all developmental stages. To study the regulation of this cardiac-specific and developmentally regulated gene in vitro, the rat cardiac troponin I gene was cloned. Transient transfection assays were performed with troponin I–luciferase fusion plasmids to characterize the regulatory regions of the gene. Proximal regions of the upstream sequence were sufficient to support high levels of expression of the reporter gene in cardiocytes and relatively low levels in other cell types. The highest luciferase activity in the cardiocytes was noted with a plasmid that included the region spanning -896 to +45 of the troponin I genomic sequence. Co-transfection of GATA-4, a recently identified cardiac transcription factor, with troponin I–luciferase constructs permitted high levels of luciferase expression in non-cardiac cells. Electrophoretic mobility-shift assays demonstrated specific binding of GATA-4 to oligonucleotides representative of multiple sites of the troponin I sequence. Mutation of a proximal GATA-4 DNA-binding site decreased transcriptional activation in transfected cardiocytes. These results indicate that the proximal cardiac troponin I sequence is sufficient to support high levels of cardiac-specific gene expression and that the GATA-4 transcription factor regulates troponin I–luciferase expression in vitro.
Reduction of Cu(II) by lipid hydroperoxides: implications for the copper-dependent oxidation of low-density lipoprotein
Authors: PATEL Rakesh P. , SVISTUNENKO Dimitri , WILSON Michael T. , DARLEY-USMAR Victor M.
Published: August 2015

The Cu(II)-promoted oxidation of lipids is a lipid hydroperoxide (LOOH)-dependent process that has been used routinely to assess the oxidizability of low-density lipoprotein (LDL) in human subjects. Metal-dependent redox reactions, including those mediated by copper, have been implicated in the pathogenesis of atherosclerosis. Despite its widespread use and possible biological significance, key elements of the mechanism are not clear. For example, although it is evident that copper acts as a catalyst, which implies a redox cycle between the Cu(II) and Cu(I) redox states, the reductants remain uncertain. In LDL these could include α-tocopherol, amino acid residues on the protein and LOOH. However, both α-tocopherol and amino acid residues are probably consumed before the most rapid phase of lipid peroxidation occurs, suggesting that another reductant must be donating electrons to Cu(II), the most likely candidate being LOOH. This role has been disputed, since LDLs nominally devoid of LOOH are still capable of reducing Cu(II) to Cu(I) and thermodynamic calculations for this reaction are not favourable. Direct investigation of the role of LOOH as reductant has not been reported and in the present study, using simple lipid systems and LDL, we have re-examined this issue using the Cu(I) chelator bathocuproine. We have shown that Cu(II) may promote lipid peroxidation in liposomes, which do not contain either protein or α-tocopherol, and that this is associated with reduction to Cu(I). The data also indicate that an equilibrium between free Cu(II) and LOOH exists, which only in the presence of an oxidizable substrate, i.e. unsaturated fatty acids, is shifted towards formation of Cu(I) and lipid-derived peroxyl radicals. We propose that reduction of Cu(II) by LOOH is a necessary component in sustaining the propagation of lipid peroxidation and that the formation of peroxyl radicals and their products in a lipid environment is sufficient to overcome thermodynamic barriers to the reaction.
cAMP prevents the glucose-mediated stimulation of GLUT2 gene transcription in hepatocytes
Authors: RENCUREL Franck , WAEBER Gérard , BONNY Christophe , ANTOINE Bénédicte , MAULARD Paulette , GIRARD Jean , LETURQUE Armelle
Published: August 2015

Glucose homoeostasis necessitates the presence in the liver of the high Km glucose transporter GLUT2. In hepatocytes, we and others have demonstrated that glucose stimulates GLUT2 gene expression in vivo and in vitro. This effect is transcriptionally regulated and requires glucose metabolism within the hepatocytes. In this report, we further characterized the cis-elements of the murine GLUT2 promoter, which confers glucose responsiveness on a reporter gene coding the chloramphenicol acetyl transferase (CAT) gene. 5´-Deletions of the murine GLUT2 promoter linked to the CAT reporter gene were transfected into a GLUT2 expressing hepatoma cell line (mhAT3F) and into primary cultured rat hepatocytes, and subsequently incubated at low and high glucose concentrations. Glucose stimulates gene transcription in a manner similar to that observed for the endogenous GLUT2 mRNA in both cell types; the -1308 to -212 bp region of the promoter contains the glucose-responsive elements. Furthermore, the -1308 to -338 bp region of the promoter contains repressor elements when tested in an heterologous thymidine kinase promoter. The glucose-induced GLUT2 mRNA accumulation was decreased by dibutyryl-cAMP both in mhAT3F cells and in primary hepatocytes. A putative cAMP-responsive element (CRE) is localized at the -1074/-1068 bp region of the promoter. The inhibitory effect of cAMP on GLUT2 gene expression was observed in hepatocytes transfected with constructs containing this CRE (-1308/+49 bp fragment), as well as with constructs not containing the consensus CRE (-312/+49 bp fragment). This suggests that the inhibitory effect of cAMP is not mediated by the putative binding site located in the repressor fragment of the GLUT2 promoter. Taken together, these data demonstrate that the elements conferring glucose and cAMP responsiveness on the GLUT2 gene are located within the -312/+49 region of the promoter.
Molecular cloning and characterization of the thiolesterase glyoxalase II from Arabidopsis thaliana
Authors: RIDDERSTRÖM Marianne , MANNERVIK Bengt
Published: August 2015

cDNA encoding glyoxalase II from Arabidopsis thalianahas been cloned and sequenced. The isolated 894 bp segment included a sequence of 774 bp encoding a protein with a calculated molecular mass of 28791 Da. The amino acid sequence deduced from the A. thalianacDNA showed 54% identity with that of the human enzyme. Searches in databanks identified seven additional DNA sequences from different species with high similarity to glyoxalase II. Certain limited regions, one rich in histidine residues, shared 100% identity. A 29 kDa protein with an isoelectric point of 6.2 was obtained by heterologous expression of the A. thalianacDNA in Escherichia coli. Homogeneous enzyme was obtained by affinity purification and its catalytic parameters with thiolesters of glutathione were similar to those for human glyoxalase II. The structural and functional similarities between glyoxalase II from A. thalianaand from human tissues suggest a common evolutionary origin.
Characterization of a saporin isoform with lower ribosome-inhibiting activity
Authors: FABBRINI M. Serena , RAPPOCCIOLO Emilia , CARPANI Daniela , SOLINAS Michela , VALSASINA Barbara , BREME Umberto , CAVALLARO Ugo , NYKJAER Anders , ROVIDA Ermanna , LEGNAME Giuseppe , SORIA Marco R.
Published: August 2015

We have expressed in Escherichia coli five isoforms of saporin, a single-chain ribosome-inactivating protein (RIP). Translation inhibition activities of the purified recombinant polypeptides in vitrowere compared with those of recombinant dianthin 30, a less potent and closely related RIP, and of ricin A chain. Dianthin 30, and a saporin isoform encoded by a cDNA from leaf tissue (SAP-C), both had about one order of magnitude lower activity in translation inhibition assays than all other isoforms of saporin tested. We recently demonstrated that saporin extracted from seeds of Saponaria officinalis binds to α2-macroglobulin receptor (α2MR; also termed low density lipoprotein-receptor-related-protein), indicating a general mechanism of interaction of plant RIPs with the α2MR system [Cavallaro, Nykjaer, Nielsen and Soria (1995) Eur. J. Biochem. 232, 165–171]. Here we report that SAP-C bound to α2MR equally well as native saporin. However, the same isoform had about ten times lower cytotoxicity than the other saporin isoforms towards different cell lines. This indicates that the lower cell-killing ability of the SAP-C isoform is presumably due to its altered interaction with the protein synthesis machinery of target cells. Since saporin binding to the α2MR is competed by heparin, we also tested in cell-killing experiments Chinese hamster ovary cell lines defective for expression of either heparan sulphates or proteoglycans. No differences were observed in cytotoxicity using native saporin or the recombinant isoforms. Therefore saporin binding to the cell surface should not be mediated by interaction with proteoglycans, as is the case for other α2MR ligands.
Recombinant expression and isolation of human l-arginine:glycine amidinotransferase and identification of its active-site cysteine residue
Authors: HUMM Andreas , FRITSCHE Erich , MANN Karlheinz , GÖHL Martin , HUBER Robert
Published: August 2015

Creatine and its phosphorylated form play a central role in the energy metabolism of muscle and nerve tissues. l-Arginine: glycine amidinotransferase (AT) catalyses the committed step in the formation of creatine. The mitochondrial and cytosolic forms of the enzyme are believed to derive from the same gene by alternative splicing. We have expressed recombinant human AT in Escherichia coliwith two different N-termini, resembling the longest two forms of the enzyme that we had isolated recently from porcine kidney mitochondria as a mixture. The enzymes were expressed with N-terminal histidine tags followed by factor Xa-cleavage sites. We established a new method for the removal of N-terminal fusion peptides by means of an immobilized snake venom prothrombin activator. We identified cysteine-407 as the active-site residue of AT by radioactive labelling and isolation of labelled peptides, and by site-directed mutagenesis of the protein.
Cytoplasmic Ca2+ signalling and reduction of mitochondrial pyridine nucleotides in adrenal glomerulosa cells in response to K+, angiotensin II and vasopressin
Authors: ROHÁCS Tibor , NAGY György , SPÄT András
Published: August 2015

We have examined the mitochondrial formation of NAD(P)H in rat adrenal glomerulosa cells. A short-term elevation of the K+ concentration from 3.6 to 8.4 mM induced a reversible increase in the formation of reduced pyridine nucleotides. Potassium applied after the addition of rotenone had no further effect, confirming that the redox signal was of mitochondrial origin. Inhibition of aldosterone synthesis by aminoglutethimide in K+-stimulated cells decreased the rate of decay of the NAD(P)H signal upon the termination of stimulation, indicating that the NADPH formed was consumed in aldosterone synthesis. When the NAD(P)H signal was measured simultaneously with the cytoplasmic free Ca2+ concentration ([Ca2+]i), elevation of the K+ concentration to 6.6 or 8.4 mM induced parallel increases in [Ca2+]i and NAD(P)H formation. The rates of increase and decrease of NAD(P)H were lower than for [Ca2+]i, confirming that the redox signal was secondary to the Ca2+ signal. Angiotensin II (100 pM–1 nM) induced an oscillatory NAD(P)H signal which usually returned to a lower baseline concentration, while a sustained signal with superimposed oscillations was observed at higher concentrations. Simultaneous measurements showed that NAD(P)H levels followed the [Ca2+]i pattern evoked by angiotensin II. Vasopressin (100 nM) also induced parallel oscillations of [Ca2+]i and NAD(P)H. A sustained rise in the extramitochondrial Ca2+ concentration to 1 μM induced a sustained elevation of the intramitochondrial Ca2+ concentration in permeabilized cells, as measured with rhod-2. A sustained rise in [Ca2+]i evoked by long-term stimulation with 8.4 mM K+ or 2.5 nM angiotensin II resulted in sustained NAD(P)H production. These Ca2+-dependent changes in the mitochondrial redox state support the biological response, i.e. aldosterone secretion by glomerulosa cells.
Study of the interactions of cadmium and zinc ions with cellular calcium homoeostasis using 19F-NMR spectroscopy
Authors: BENTERS Jelko , FLÖGEL Ulrich , SCHÄFER Thorsten , LEIBFRITZ Dieter , HECHTENBERG Stefan , BEYERSMANN Detmar
Published: August 2015

The effects of the heavy-metal ions Cd2+ and Zn2+ on the homoeostasis of intracellular free Ca2+ in E367 neuroblastoma cells were examined using 19F-NMR spectroscopy with the fluorinated chelator probe 1,2-bis-(2-amino-5-fluorophenoxy)ethane-N,N,N´,N´-tetra-acetic acid (5F-BAPTA). First, the technique was used to quantify the uptake and intracellular free concentrations of the heavy metals after treatment of the cells with 20 μM CdCl2 or 100 μM ZnCl2. Secondly, metal-induced transients in intracellular free Ca2+ were recorded. Addition of 20 μM CdCl2, but not 100 μM ZnCl2, evoked a transient increase in Ca2+ from a resting level of 84 nM to approx. 190 nM within 15 min after addition of the metal. Zn2+ at 20 μM completely prevented the induction of a Ca2+ transient by Cd2+. Ca2+ was mobilized by Cd2+ from intracellular organelles, since depletion of these stores by thapsigargin abolished the effect of the toxic metal. Furthermore, 20 μM Cd2+ evoked a transient rise in cellular Ins(1,4,5)P3, reaching a maximum level within 5 min after addition of the metal. These results demonstrate that perturbation of the Ins(1,4,5)P3/Ca2+ messenger system is an early and discrete cellular effect of Cd2+.
Benzyloxycarbonylprolylprolinal, a transition-state analogue for prolyl oligopeptidase, forms a tetrahedral adduct with catalytic serine, not a reactive cysteine
Authors: KAHYAOGLU Ara , HAGHJOO Khadijeh , KRAICSOVITS Ferenc , JORDAN Frank , POLGAR Laszlo
Published: August 2015

N-Benzyloxycarbonyl-l-prolyl-l-[1-13C]prolinal was synthesized starting with reduction of l-[1-13C]Pro to l-[1-13C]prolinol, followed by coupling with N-benzyloxycarbonyl-l-Pro to N-benzyloxycarbonyl-l-Pro-l-[1-13C]prolinol (Z-Pro-[1-13C]prolinol), and finally oxidation of the alcohol to the aldehyde with dimethyl sulphoxide. While the 13C NMR chemical shift of the aldehyde carbon is 202 p.p.m., that of the aldehyde hydrate is between 91.6 and 91.8 p.p.m., that of the dithiothreitol adduct is between 74.8 and 75.0 p.p.m., and that in the presence of the serine protease prolyl oligopeptidase is at 92.3 p.p.m.. The linewidth of the latter is 114 Hz, roughly consistent with the molecular mass of 80 kDa reported for the enzyme. Inverse detection experiments gave a 1H resonance at 5.29 p.p.m. with a linewidth of 80 Hz, also consistent with the expected chemical shift and linewidth for a hemiacetal bound to such a large enzyme, while the free hydrate gave resonances at 5.18 and 5.25 p.p.m., with very much narrower linewidths. It is concluded that Z-Pro-prolinal, a putative transition-state analogue for prolyl oligopeptidase, forms a tetrahedral complex with the enzyme at its catalytic serine, rather than at a neighbouring cysteine that was found to be highly reactive according to chemical modification studies.
Identification of the epitope for a monoclonal antibody that blocks platelet aggregation induced by type III collagen
Authors: GLATTAUER Veronica , WERKMEISTER Jerome A. , KIRKPATRICK Alan , RAMSHAW John A. M.
Published: August 2015

A library of eight conformation-dependent monoclonal antibodies that react with distinct epitopes on native human type III collagen has been examined for the ability of these antibodies to inhibit platelet aggregation induced by this collagen. Six of these antibodies had no effects; one, 1E7-D7/Col3, delayed the onset and slowed the rate of platelet aggregation, while another, 2G8-B1/Col3, completely inhibited aggregation. In order to identify the epitope recognized by this inhibitory antibody, a series of peptides that could fold to form triple-helical fragments was examined. Each peptide included six Gly-Xaa-Yaa triplets from the human type III collagen sequence, where Xaa and Yaa represent the particular amino acids in the sequence, and a C-terminal (Gly-Pro-Hyp)4 sequence to enhance triple-helical stability. Using these peptides we have identified the epitope as a nine-amino-acid sequence, GLAGAOGLR (where O is the one-letter code for 4-hydroxyproline), starting at position 520 in the human type III collagen helical domain. This sequence is proximal to the site proposed for the interaction of type III collagen with α2β1-integrin of platelets.
N-terminal type I modules required for fibronectin binding to fibroblasts and to fibronectin's III1 module
Authors: SOTTILE Jane , MOSHER Deane F.
Published: August 2015

Assembly of fibronectin fibrils occurs at the surface of substrate-attached cells and is mediated by the first to the fifth type I modules in the N-terminal 70 kDa portion of the molecule. The first type III module (III1) of fibronectin, not present in the 70 kDa portion, contains a conformation-dependent binding site for the 70 kDa N-terminal region of fibronectin, suggesting that the III1 module on cell-surface fibronectin may serve as a binding site for fibronectin's N-terminus on substrate-attached cells. To explore this possiblility, we compared the ability of mutant recombinant 70 kDa proteins containing deletions of one or several of the first five type I modules to bind to fibroblasts and to III1. Proteins containing the fourth and fifth type I modules (70KΔI1-3) bound specifically to III1 in solid-phase binding assays; proteins lacking I4 and I5 did not bind. N-terminal molecules containing the fourth and fifth type I modules also bound to fibroblasts, suggesting that III1-like binding sites are present on the cell surface. However, the high-affinity binding sites on fibroblasts for fibronectin or the 70 kDa protein displayed more complex determinants, inasmuch as 70 kDa deletion mutants lacking I4 and I5 also bound to the cell surface, and deletion mutants lacking I1-3 and I4-5 both competed only partially for binding of 125I-labelled fibronectin or 70 kDa protein. These data indicate that the N-terminal part of fibronectin binds to III1 via I4 and I5 and that interactions in addition to that of I4 and I5 with III1 are important for cell-surface-mediated fibronectin polymerization.
Evidence for multiple forms of biotin holocarboxylase synthetase in pea (Pisum sativum) and in Arabidopsis thaliana: subcellular fractionation studies and isolation of a cDNA clone
Authors: TISSOT Ghislaine , DOUCE Roland , ALBAN Claude
Published: August 2015

The intracellular compartmentation of biotin holocarboxylase synthetase has been investigated in pea (Pisum sativum) leaves, by isolation of organelles and fractionation of protoplasts. Enzyme activity was mainly located in cytosol (approx. 90% of total cellular activity). Significant activity was also identified in the soluble phase of both mitochondria and chloroplasts. Two enzyme forms were separated by anion-exchange chromatography. The major form was found to be specific for the cytosol compartment, whereas the minor form was present in mitochondria as well as in chloroplasts. We also report the isolation and DNA sequence of a cDNA encoding an Arabidopsis thaliana biotin holocarboxylase synthetase. This cDNA was isolated by functional complementation of a conditional lethal Escherichia coli birA (biotin ligase gene, which regulates biotin synthesis) mutant. This indicated that the recombinant plant protein was able to biotinylate specifically an essential apoprotein substrate in the bacterial host, that is a subunit of acetyl-CoA carboxylase called biotin carboxyl carrier protein. The full-length nucleotide sequence (1534 bp) encodes a protein of 367 amino acid residues with a molecular mass of 41172 Da and shows specific regions of similarity to other biotin holocarboxylase synthetase genes as isolated from bacteria and yeast, and with cDNA species from human. A sequence downstream of the first translation initiation site encodes a putative peptide structurally similar to organelle-targeting pre-sequences, suggesting a mitochondrial or chloroplastic localization for this isoform.
Stability of a thermophilic TIM-barrel enzyme: indole-3-glycerol phosphate synthase from the thermophilic archaeon Sulfolobus solfataricus
Authors: ANDREOTTI Giuseppina , CUBELLIS M. Vittoria , DI PALO Michela , FESSAS Dimitrios , SANNIA Giovanni , MARINO Gennaro
Published: August 2015

The stability and activity of indole-3-glycerol phosphate synthase from Sulfolobus solfataricus were studied as a function of pH and temperature. In this paper we focus on three points: (1) the long-term stability of the protein to irreversible denaturation at high temperature; (2) the short-term stability of the protein to reversible temperature-driven unfolding; and (3) the dependence of its activity on temperature. Results can be summarized as follows: (a) the same first-order kinetic constant (0.020±0.003 min-1) was determined at different pH values (6.5, 8.0 and 9.5) from long-term stability experiments at 80 °C; (b) short-term stability experiments revealed different behaviour in two different pH ranges (6.5-8.0, 8.5-9.5), suggesting that the melting temperature is higher at alkaline than at neutral pH; (c) the dependence of activity on temperature was investigated at pH 7.0 and 9.0, and a discontinuity was observed in the Arrhenius plot of kcat values at pH 9.0. We also investigated the stability in the presence of guanidinium chloride at 20 °C either at pH 7.0 or at pH 9.0, and we present data that indicate that the unfolding mechanism closely approaches a two-state model at pH 7.0 and a more complex mechanism at pH 9.0. Satisfactory fitting of the equilibrium unfolding transition obtained by fluorescence measurements at pH 9.0 required a model that involves a stable intermediate in addition to the native and unfolded forms. At 20 °C the folded conformation is more stable than the unfolded conformation by (14.7±1.2) kJ/mol at pH 7.0 and by (25.5±1.8) kJ/mol at pH 9.0.
Cytosolic phospholipase A2 is coupled to muscarinic receptors in the human astrocytoma cell line 1321N1: characterization of the transducing mechanism
Authors: BAYON Yolanda , HERNANDEZ Marita , ALONSO Andrés , NUÑEZ Lucía , GARCIA-SANCHO Javier , LESLIE Christina , CRESPO Mariano SANCHEZ , NIETO María Luisa
Published: August 2015

The cholinergic agonist carbachol induced the release of arachidonic acid in the 1321N1 astrocytoma cell line, and this was blocked by atropine, suggesting the involvement of muscarinic receptors. To assess the mechanisms of signalling involved in the response to carbachol, a set of compounds characterized by eliciting responses through different mechanisms was tested. A combination of 4β-phorbol 12β-myristate 13α-acetate and thapsigargin, an inhibitor of endomembrane Ca2+-ATPase that induces a prolonged elevation of cytosolic Ca2+ concentration, induced an optimal response, suggesting at first glance that both protein kinase C (PKC) and Ca2+ mobilization were involved in the response. This was consistent with the observation that carbachol elicited Ca2+ mobilization and PKC-dependent phosphorylation of cytosolic phospholipase A2 (cPLA2; phosphatide sn-2-acylhydrolase, EC 3.1.1.4) as measured by a decrease in electrophoretic mobility. Nevertheless, the release of arachidonate induced by carbachol was unaltered in media containing decreased concentrations of Ca2+ or in the presence of neomycin, a potent inhibitor of phospholipase C which blocks phosphoinositide turnover and Ca2+ mobilization. Guanosine 5´-[γ-thio]triphosphate added to the cell-free homogenate induced both [3H]arachidonate release and cPLA2 translocation to the cell membrane fraction in the absence of Ca2+, thus suggesting the existence of an alternative mechanism of cPLA2 translocation dependent on G-proteins and independent of Ca2+ mobilization. From the combination of experiments utilizing biochemical and immunological tools the involvement of cPLA2 was ascertained. In summary, these data indicate the existence in the astrocytoma cell line 1321N1 of a pathway involving the cPLA2 which couples the release of arachidonate to the occupancy of receptors for a neurotransmitter, requires PKC activity and G-proteins and might operate in the absence of Ca2+ mobilization.
Identification of isoforms of the exocytosis-sensitive phosphoprotein PP63/parafusin in Paramecium tetraurelia and demonstration of phosphoglucomutase activity
Authors: HAUSER Karin , KISSMEHL Roland , LINDER Jürgen , SCHULTZ Jochen E. , LOTTSPEICH Friedrich , PLATTNER Helmut
Published: August 2015

PP63 (parafusin) is a 63 kDa phosphoprotein which is very rapidly (within 80 ms) dephosphorylated (to P63) during triggered trichocyst exocytosis; this occurs selectively in exocytosis-competent Paramecium tetraurelia strains. In the present work, two cDNAs coding for PP63/parafusin have been isolated, one of which is a new isoform. These isoforms are 99.6% identical and are derived from two different genes. Similarity searches revealed 43-51% identity of the deduced amino acid sequences with known phosphoglucomutases from yeast and mammals. The sequences of two proteolytic peptides obtained from PP63/parafusin isolated from Paramecium are identical to parts of the amino acid sequence deduced from the major cDNA. The major cDNA was mutated from the macronuclear ciliate genetic code into the universal genetic code and expressed in Escherichia coli. The recombinant protein shows the same biochemical and immunological characteristics as the (P)P63/parafusin originally isolated from Paramecium. It has the same specific phosphoglucomutase activity as phosphoglucomutase from chicken muscle. We also show that recombinant P63-1/parafusin 1 is a substrate of an endogenous casein kinase from Paramecium, as is the originally isolated P63/parafusin. Polyclonal antibodies against recombinant P63-1/parafusin 1 were raised which recognized phosphoglucomutases from different sources. Thus we show that PP63/parafusin and phosphoglucomutase in Paramecium are identical.
A nonsense mutation in the 3-hydroxy-3-methylglutaryl-CoA lyase gene produces exon skipping in two patients of different origin with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency
Authors: PIÉ Juan , CASALS Núria , CASALE Cesar H. , BUESA Carlos , MASCARÓ Cristina , BARCELÓ Anna , ROLLAND Marie-Odile , ZABOT Theresa , HARO Diego , EYSKENS François , DIVRY Priscille , HEGARDT Fausto G.
Published: August 2015

A novel nonsense mutation associated with the skipping of constitutive exon 2 of the 3-hydroxy-3-methylglutaryl-CoA lyase gene was found in two patients, from Portugal and Morocco, with 3-hydroxy-3-methylglutaric acidemia. By reverse transcriptase PCR and single-strand conformational polymorphism a G–T transversion was located, at nucleotide 109, of the 3-hydroxy-3-methylglutaryl-CoA lyase cDNA, within exon 2. Two mRNAs were produced as a result of this nonsense mutation: one of the expected size that contains the premature stop codon UAA, and the other with a deletion of 84 bp corresponding to the whole of exon 2. This deletion produced the loss of the last seven amino acids of the leader peptide and the first 21 amino acids of the mature protein. The nonsense mutation was found in a purine-rich GGAAG sequence, which is equal to, or similar to, others reported to be exonic splicing enhancers (ESE). We suggest that the nonsense mutation may affect a possible ESE on exon 2, which would hinder the splice site selection and facilitate an aberrant splice with the skipping of this exon. Determination by quantitative PCR shows that the ratio of mRNA with the nonsense mutation to the mRNA with the deletion is approx. 3:1.
Cloning, sequencing and expression of rat liver 3-phosphoglycerate dehydrogenase
Authors: ACHOURI Younes , RIDER Mark H. , VAN SCHAFTINGEN Emile , ROBBI Mariette
Published: August 2015

Rat liver d-3-phosphoglycerate dehydrogenase was purified to homogeneity and digested with trypsin, and the sequences of two peptides were determined. This sequence information was used to screen a rat hepatoma cDNA library. Among 11 positive clones, two covered the whole coding sequence. The deduced amino acid sequence (533 residues; Mr 56493) shared closer similarity with Bacillus subtilis 3-phosphoglycerate dehydrogenase than with the enzymes from Escherichia coli, Haemophilus influenzae and Saccharomyces cerevisiae. In all cases the similarity was most apparent in the substrate- and NAD+-binding domains, and low or insignificant in the C-terminal domain. A corresponding 2.1 kb mRNA was present in rat tissues including kidney, brain and testis, whatever the dietary status, and also in livers of animals fed a protein-free, carbohydrate-rich diet, but not in livers of control rats, suggesting transcriptional regulation. The full-length rat 3-phosphoglycerate dehydrogenase was expressed in E. coli and purified. The recombinant enzyme and the protein purified from liver displayed hyperbolic kinetics with respect to 3-phosphoglycerate, NAD+ and NADH, but substrate inhibition by 3-phosphohydroxypyruvate was observed; this inhibition was antagonized by salts. Similar properties were observed with a truncated form of 3-phosphoglycerate dehydrogenase lacking the C-terminal domain, indicating that the latter is not implicated in substrate inhibition or in salt effects. By contrast with the bacterial enzyme, rat 3-phosphoglycerate dehydrogenase did not catalyse the reduction of 2-oxoglutarate, indicating that this enzyme is not involved in human d- or l-hydroxyglutaric aciduria.
ATP synthase subunit c expression: physiological regulation of the P1 and P2 genes
Authors: ANDERSSON Ulf , HOUŠTĚK Josef , CANNON Barbara
Published: August 2015

Pre-translational regulation of subunit c has been suggested to control the biosynthesis of mitochondrial ATP synthase (ATPase) in brown adipose tissue (BAT). Subunit c is encoded by the genes P1 and P2, which encode identical mature proteins. We have determined here the levels of P1 and P2 mRNAs in different tissues, in response to cold acclimation in rats, during ontogenic development of BAT in hamsters, and following thyroid hormone treatment in rat BAT and liver. Quantitative ribonuclease protection analysis showed that both the P1 and P2 mRNAs were present in all rat tissues measured. Their total amount in each tissue corresponded well with the ATPase content of that tissue. While the P1/P2 mRNA ratio is high in ATPase-rich tissues, the P2 mRNA dominates in tissues with less ATPase. Cold acclimation affects P1 but not P2 gene expression in rat BAT. A rapid and transient increase in P1 mRNA is followed by sustained depression, which is accompanied by a decrease in ATPase content. Similarly, ontogenic suppression of ATPase content in hamster BAT was accompanied by suppression of the P1 mRNA levels, while P2 expression was virtually unchanged. Furthermore, when hypothyroid rats were treated with thyroid hormone, the steady-state level of P1 but not of P2 mRNA was significantly increased in liver. BAT was unaffected. We conclude that the P1 and P2 genes for subunit c are differentially regulated in vivo. While the P2 gene is expressed constitutively, the P1 gene responds to different physiological stimuli as a means of modulating the relative content of ATP synthase.
Regulation of N-linked core glycosylation: use of a site-directed mutagenesis approach to identify Asn-Xaa-Ser/Thr sequons that are poor oligosaccharide acceptors
Authors: KASTURI Lakshmi , CHEN Hegang , SHAKIN-ESHLEMAN Susan H.
Published: August 2015

N-linked glycosylation can profoundly affect protein expression and function. N-linked glycosylation usually occurs at the sequon Asn-Xaa-Ser/Thr, where Xaa is any amino acid residue except Pro. However, many Asn-Xaa-Ser/Thr sequons are glycosylated inefficiently or not at all for reasons that are poorly understood. We have used a site-directed mutagenesis approach to examine how the Xaa and hydroxy (Ser/Thr) amino acid residues in sequons influence core-glycosylation efficiency. We recently demonstrated that certain Xaa amino acids inhibit core glycosylation of the sequon, Asn37-Xaa-Ser, in rabies virus glycoprotein (RGP). Here we examine the impact of different Xaa residues on core-glycosylation efficiency when the Ser residue in this sequon is replaced with Thr. The core-glycosylation efficiencies of RGP variants with different Asn37-Xaa-Ser/Thr sequons were compared by using a cell-free translation/glycosylation system. Using this approach we confirm that four Asn-Xaa-Ser sequons are poor oligosaccharide acceptors: Asn-Trp-Ser, Asn-Asp-Ser, Asn-Glu-Ser and Asn-Leu-Ser. In contrast, Asn-Xaa-Thr sequons are efficiently glycosylated, even when Xaa = Trp, Asp, Glu or Leu. A comparison of the glycosylation status of Asn-Xaa-Ser and Asn-Xaa-Thr sequons in other glycoproteins confirms that sequons with Xaa = Trp, Asp, Glu or Leu are rarely glycosylated when Ser is the hydroxy amino acid residue, and that these sequons are unlikely to serve as glycosylation sites when introduced into proteins by site-directed mutagenesis.
Biochemical characterization of the arginine-specific proteases of Porphyromonas gingivalis W50 suggests a common precursor
Authors: RANGARAJAN Minnie , SMITH Susan J. M. , U Sally , CURTIS Michael A.
Published: August 2015

Extracellular proteases of Porphyromonas gingivalis specific for arginyl peptide bonds are considered to be important virulence factors in periodontal disease. In order to determine the number, inter-relationship and kinetic properties of these proteases, extracellular enzymes with this peptide-bond specificity were purified and characterized from P. gingivalis W50. Three forms, which we denote RI, RI-A and RI-B, accounted for all of the activity in the supernatant. All three enzymes contain an α chain of ∼54 kDa with the same N-terminal amino acid sequence. RI is a heterodimer of non-covalently linked α and β chains which migrate to the same position on SDS/PAGE but which can be resolved by 8 M urea/PAGE. RI-A and RI-B are both monomeric, but the molecular mass of RI-B (70–80 kDa) is significantly increased due to post-translational modification with lipopolysaccharide. All forms show absolute specificity for peptide bonds with Arg in the P1 position and are also capable of hydrolysing N-terminal Arg and C-terminal Arg–Arg peptide bonds. Thus they show limited amino- and carboxy-peptidase activity. For the hydrolysis of Nα-benzoyl-l-Arg-p-nitroanilide, the pH optimum is 8.0 at 30 °C. The Vmax for all three enzymes is controlled by ionization of two residues with apparent pKas at 30 °C of 6.5±0.05 and 9.7±0.05, and ΔH values of ∼29 kJ/mol and ∼ 24 kJ/mol in the enzyme–substrate complex. By analogy with papain, the pKa of 6.5 could be ascribed to a Cys and the pKa of 9.7 to a His residue. E-64 [l-trans-epoxysuccinyl-leucylamide-4-(4-guanidino)butane] is a competitive inhibitor of RI, RI-A and RI-B. Based on physical properties and kinetic behaviour, RI-A appears to be analogous to gingipain from P. gingivalis HG66. However the α/β structure of RI differs significantly from that of the high-molecular-mass multimeric complex of gingipain containing four haemagglutinins described by others. Since the genes for RI and high-molecular-mass gingipain are identical, the data indicate that an alternative processing pathway is involved in the formation of RI from the initial precursor. Furthermore, the identical N-termini and enzymic properties of the catalytic component of RI, RI-A and RI-B suggest that the maturation pathway of the RI precursor may also give rise to RI-A and RI-B. The physiological functions of these isoforms and their role in the disease process may become more apparent through examination of their interactions with host proteins.
Subcellular localization and function of melanogenic enzymes in the ink gland of Sepia officinalis
Authors: PALUMBO Anna , COSMO Anna DI , GESUALDO Ida , HEARING Vincent J.
Published: August 2015

The ink gland of the cuttlefish Sepia officinalis has traditionally been regarded as a convenient model system for investigating melanogenesis. This gland has been shown to contain a variety of melanogenic enzymes including tyrosinase, a dopachrome-rearranging enzyme and peroxidase. However, whether and to what extent these enzymes co-localize in the melanogenic compartments and interact is an open question. Using polyclonal antibodies that recognize the corresponding Sepia proteins, we have been able to demonstrate that peroxidase has a different subcellular localization pattern from tyrosinase and dopachrome-rearranging enzyme. Whereas peroxidase is located in the rough endoplasmic reticulum and in the matrix of premelanosomes and melanosomes, tyrosinase and dopachrome-rearranging enzyme are present in the rough endoplasmic reticulum–Golgi transport system, at the level of trans-Golgi cisternae, trans-Golgi network and coated vesicles, and in melanosomes on pigmented granules. These results fill a longstanding gap in our knowledge of the melanin-producing system in Sepia and provide the necessary background for dissection at the molecular level of the complex interaction between melanogenic enzymes. Moreover, the peculiar and complex organization of melanin in an invertebrate such as Sepia officinalis is surprising and could provide the basis for understanding the process in more evolved systems such as that of mammals.