Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.4.99.7 (sialyltransferase)
1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Golgi vesicles were isolated and purified from rat liver, in which the specific activities of glycosyltransferases (e.g. GM3:CMP-NeuAc sialyltransferase, GD3 synthase; GM3:UDP-GalNAc galactosaminyltransferase, GM2 synthase) were 50-60-times enriched relative to microsomes or total homogenate. Synthesis of gangliosides GM2 and GM1 in such Golgi vesicles is, in the absence of any detergents, stimulated 6-fold and 20-fold respectively by phosphatidylglycerol. Other phospholipids like phosphatidylethanolamine and phosphatidylserine are also significantly stimulatory. With 50 micrograms Golgi protein and 1 nmol UDP-GalNAc, optimal stimulation of GM2 synthase was obtained with 20 micrograms of phosphatidylglycerol and 7.5 nmol of the lipid acceptor GM3. Under the same experimental conditions this stimulation exceeds (by about 40%) that obtained with optimal amount (200 micrograms) of the detergent octylglucoside. Phosphatidylglycerol, on the other hand, has virtually no stimulatory activity on the synthesis of ganglioside GD3 either in the presence of Mg2+ or Mn2+, indicating that facilitation by phospholipid of GM3 transport into Golgi vesicles was not the basis of stimulation of GM2 synthesis. Tunicamycin inhibits the synthesis of gangliosides GM2 and GM1 in isolated Golgi vesicles, but only in the absence of detergents. In the presence of phosphatidylglycerol, GM2 synthesis, for example, was inhibited by 60% by 2 micrograms tunicamycin and more than 85% by 10 micrograms tunicamycin, per 50 micrograms Golgi membrane protein. The inhibition was stronger on GM1 synthesis: 85% with 2.5 micrograms of the antibiotic. The dependence on phosphatidylglycerol and the degree of inhibition by tunicamycin of the synthetic activities are strictly dependent on the intactness of the Golgi vesicles: both phenomena become increasingly less evident when the vesicles are pelleted, and frozen and thawed several times, and completely disappear when the vesicles are solubilized by detergents or disrupted by ultrasonication. Furthermore, tunicamycin inhibition is reversible by increased concentration of phosphatidylglycerol. All these results indicate that phosphatidylglycerol does not stimulate, and tunicamycin does not inhibit, the transferases themselves; rather, the two opposing effects might relate to carrier-mediated transport, e.g. of nucleotide sugars, across Golgi vesicles.
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PMID:Ganglioside biosynthesis in Golgi apparatus of rat liver. Stimulation by phosphatidylglycerol and inhibition by tunicamycin. 686 62

It was previously reported that monosialosylgangliopentaosyl ceramide (GalNAc-GM1b) was a major ganglioside in Xenopus laevis oocytes. Here we determined biosynthetic pathways for the ganglioside by detailed measurements of glycosyltransferase activities. CMP-NeuAc:asialo-GM1 alpha 2-3 sialyltransferase (alpha 2-3 ST) and UDP-GalNAc:GM1b beta 1-4 N-acetylgalactosaminyltransferase (beta 1-4 GalNAcT) exhibited much higher activity than CMP-NeuAc:GalNAc-GA1 alpha 2-3 ST and UDP-GalNAc:asialo-GM1 beta 1-4 GalNAcT, respectively. These observations indicated the existence of a unique biosynthetic pathway in the oocytes as follows; asialo-GM1-->GM1b-->GalNAc-GM1b.
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PMID:A unique biosynthetic pathway for gangliosides exists in Xenopus laevis oocytes. 792 15

Many Golgi glycosyltransferases are type II membrane proteins which are cleaved to produce soluble forms that are released from cells. Cho and Cummings recently reported that a soluble form of alpha1, 3-galactosyltransferase was comparable to its membrane bound counterpart in its ability to galactosylate newly synthesized glycoproteins (Cho,S.K. and Cummings,R.D. (1997) J. Biol. Chem., 272, 13622-13628). To test the generality of their findings, we compared the activities of the full length and soluble forms of two such glycosyltransferases, ss1,4 N-Acetylgalactosaminyltransferase (GM2/GD2/ GA2 synthase; GalNAcT) and beta galactoside alpha2,6 sialyltransferase (alpha2,6-ST; ST6Gal I), for production of their glycoconjugate products in vivo . Unlike the full length form of GalNAcT which produced ganglioside GM2 in transfected cells, soluble GalNAcT did not produce detectable GM2 in vivo even though it possessed in vitro GalNAcT activity comparable to that of full length GalNAcT. When compared with cells expressing full length alpha2,6-ST, cells expressing a soluble form of alpha2,6-ST contained 3-fold higher alpha2,6-ST mRNA levels and secreted 7-fold greater alpha2,6-ST activity as measured in vitro , but in striking contrast contained 2- to 4-fold less of the alpha2,6-linked sialic acid moiety in cellular glycoproteins in vivo . In summary these results suggest that unlike alpha1,3-galactosyltransferase the soluble forms of these two glycosyltransferases are less efficient at glycosylation of membrane proteins and lipids in vivo than their membrane bound counterparts.
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PMID:Two soluble glycosyltransferases glycosylate less efficiently in vivo than their membrane bound counterparts. 963 44

Cell differentiation is frequently accompanied by alterations in the composition of gangliosides in the plasma membrane resulting from a regulation of the enzyme activities involved. The regulation of CMP-NeuAc:GM1 alpha2-3-sialyltransferase (ST-IV) and UDP-GalNAc:GM3 N-acetylgalactosaminyltransferase (Gal-NAc-T) by the degree of enzyme phosphorylation was analyzed by determination of the enzyme activity on incubation of NG108-15 cells with various protein phosphatase inhibitors (okadaic acid and orthovanadate) or protein kinase activators (phorbol ester and forskolin). Incubation with okadaic acid, but not with orthovanadate, inhibited the ST-IV activity to 45% of that of control cells with t(1/2) = 60 min for the inactivation reaction. This indicates a rapid hyperphosphorylation of ST-IV due to the inhibition of a serine/threonine-specific phosphatase. A similar rate of inactivation was found on stimulation of protein kinase C with phorbol ester. In contrast to ST-IV, the activity of GalNAc-T was increased on stimulation of intracellular phosphorylation systems. The fastest activation of GalNAc-T was achieved with forskolin, yielding up to 160% of the initial activity within 30 min of effector incubation. Up-regulation of GalNAc-T in conjunction with down-regulation of ST-IV by stimulation of phosphorylation is suggested to serve as a physiological mechanism to increase the concentration of GM1, which was found to be elevated in correlation with the cell density. This assumption was corroborated by metabolic labeling studies with radioactive ganglioside precursors indicating an enhancement of the relative amount of a-series gangliosides subsequent to GM3 on phosphorylation stimulation. In particular, the biosynthesis of GM1 was specifically elevated within 2 h of incubation with forskolin. We conclude from the overall data that the ganglioside composition during the cell differentiation of NG108-15 cells can be specifically regulated by both protein kinase A- and protein kinase C-related phosphorylation systems.
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PMID:Regulation of ganglioside metabolism by phosphorylation and dephosphorylation. 972 22

Retinoic acid (RA) plays an important role in differentiation stage in which it also influences glycoconjugate metabolism. Previous work in our laboratory has shown that treatment with RA modifies glycolipid synthesis and distribution in total Xenopus embryos during development. In this study we have investigated the activity of the following anabolic enzymes involved in glycolipid biosynthesis: sialyltransferase-1 (SAT-1), GM3(beta1, 4)-N-acetylgalactosaminyltransferase (GalNAcT-1) and LacCer(beta1, 3)N-acetylglucosaminyltransferase (GlcNAcT-1). These enzymes are located at the branching point of lactosylceramide (Lc(2)) metabolism. Enzyme activities were assayed after treatment with different doses of RA added exogenously to the medium during the first 7 days of Xenopus embryo development. Our results show that RA activates GlcNAcT-1, the enzyme that drives Lc(2)to the glycolipids of the lacto-series, and SAT-1 that inserts Lc(2)in the ganglio-series pathway. These data support our previous analysis of glycolipid pattern in Xenopus embryos after RA treatment (Rizzo et al., 1995;Cell Biol Int19: 895-901) indicating a possible correlation between the distribution of glycolipids and the enzymes involved in their metabolism.
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PMID:Glycolipid glycosyltransferase activities during early development of Xenopus: effect of retinoic acid. 1056 Nov 17

Knockout mice lacking glycosyltransferases or sulfotransferases provide unequivocal evidence that the carbohydrate moieties of glycoproteins, glycolipids, and proteoglycans play essential roles in various biological phenomena such as development, the immune response, and tissue functions. Examples of abnormalities of null mutants include arrest of embryogenesis due to deletion of N-acetylglucosaminyltransferase I or glucosylceramide synthase, failure of kidney formation in heparan sulfate 2-O-sulfotransferase deficiency, suppressed antibody production in alpha-2, 6-sialyltransferase deficiency, male sterility in GM2/GD2 synthase deficiency, and abnormalities in the function and stability of myelin in galactosylceramide deficiency.
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PMID:Essential roles of carbohydrate signals in development, immune response and tissue functions, as revealed by gene targeting. 1073 80

Gangliosides are sialylated glycosphingolipids whose biosynthesis is catalyzed by a series of endoplasmic reticulum (ER)- and Golgi-resident glycosyltransferases. Protein expression, processing, and subcellular localization of the key regulatory enzymes for ganglioside biosynthesis, sialyltransferase II (ST-II) and N-acetylgalactosaminyltransferase I (GalNAcT), were analyzed upon transient expression of the two enzymes in the neuroblastoma cell lines NG108-15 and F-11. The enzymes were endowed with a C-terminal epitope tag peptide (FLAG) for immunostaining and immunoaffinity purification using a FLAG-specific antibody. Mature ST-II-FLAG and GalNAcT-FLAG were expressed as N-glycoproteins with noncomplex oligosaccharides. ST-II-FLAG was distributed to the Golgi apparatus, whereas GalNAcT-FLAG was found in the ER and Golgi. Inhibition of early N-glycoprotein processing with castanospermine resulted in a distribution of ST-II-FLAG to the ER, whereas that of GalNAcT-FLAG remained unaltered. In contrast to GalNAcT, the activity of ST-II and the amount of immunostained enzyme were reduced concomitantly by 75% upon incubation with castanospermine. This was due to a fourfold increased turnover of ST-II-FLAG, which was not found with GalNAcT-FLAG. The ER retention and increased turnover of ST-II-FLAG were most likely due to its inability to bind to calnexin upon inhibition of early N-glycoprotein processing. Calnexin binding was not observed for GalNAcT-FLAG, indicating a differential effect of N-glycosylation on the turnover and subcellular localization of the two glycosyltransferases.
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PMID:Effect of N-glycosylation on turnover and subcellular distribution of N-acetylgalactosaminyltransferase I and sialyltransferase II in neuroblastoma cells. 1082 Jan 96

The production of mice with genetic alterations in glycosyltransferases has highlighted the need to isolate and study complex mixtures of the major classes of oligosaccharides (glycans) from intact tissues. We have found that nano-NMR spectroscopy of whole mixtures of N- and O-glycans can complement HPLC profiling methods for elucidating structural details. Working toward obtaining such glycan mixtures from mouse tissues, we decided to develop an approach to isolate not only N- and O-glycans, but also to separate out glycosphingolipids, glycosaminoglycans and glycosylphosphatidylinositol anchors. We describe here a comprehensive Glycan Isolation Protocol that is based primarily upon the physicochemical characteristics of the molecules, and requires only commonly available reagents and equipment. Using radiolabeled internal tracers, we show that recovery of each major class of glycans is as good or better than with conventional approaches for isolating individual classes, and that cross-contamination is minimal. The recovered glycans are of sufficient purity to provide a "glycoprofile" of a cell type or tissue. We applied this approach to compare the N- and O-glycans from wild type mouse tissues with those from mice genetically deficient in glycosyltransferases. N- and O-glycan mixtures from organs of mice deficient in ST6Gal-I (CMP-Sia:Galbeta1-4GlcNAc alpha2-6 sialyltransferase) were studied by the nano-NMR spectroscopy approach, showing no detectable alpha2-6-linked sialic acids. Thus, ST6Gal-I is likely responsible for generating most or all of these residues in normal mice. Similar studies indicate that this linkage is very rare in ganglioside glycans, even in wild-type tissues. In mice deficient in GalNAcT-8 (UDP-GalNAc:polypeptide O-Ser/Thr GalNAc transferase 8), HPLC profiling indicates that O-glycans persist in the thymus in large amounts, without a major change in overall profile, suggesting that other enzymes can synthesize the GalNAc-O-Ser/Thr linkage in this tissue. These results demonstrate the applicability of nano-NMR spectroscopy to complex glycan mixtures, as well as the versatility of the Glycan Isolation Protocol, which makes possible the concurrent examination of multiple glycan classes from intact vertebrate tissues.
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PMID:Exploring the glycan repertoire of genetically modified mice by isolation and profiling of the major glycan classes and nano-NMR analysis of glycan mixtures. 1091 Sep 72

Gangliosides are a family of glycosphingolipids that contain sialic acid. Although they are abundant on neuronal cell membranes, their precise functions and importance in the central nervous system (CNS) remain largely undefined. We have disrupted the gene encoding GD3 synthase (GD3S), a sialyltransferase expressed in the CNS that is responsible for the synthesis of b-series gangliosides. GD3S-/- mice, even with an absence of b-series gangliosides, appear to undergo normal development and have a normal life span. To further restrict the expression of gangliosides, the GD3S mutant mice were crossbred with mice carrying a disrupted GalNAcT gene encoding beta1,4-N-acetylgalactosaminyltransferase. These double mutant mice expressed GM3 as their major ganglioside. In contrast to the single mutant mice, the double mutants displayed a sudden death phenotype and were extremely susceptible to induction of lethal seizures by sound stimulus. These results demonstrate unequivocally that gangliosides play an essential role in the proper functioning of the CNS.
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PMID:Mice expressing only monosialoganglioside GM3 exhibit lethal audiogenic seizures. 1113 99

The beta 1,6 N-acetylglucosaminyltransferase (C2GnT) has been recently mapped to the cis/medial-Golgi compartment. To analyze the Golgi-targeting determinants of C2GnT, we constructed various deletion mutants of the enzyme fused to the enhanced green fluorescent protein (EGFP) and localized these proteins by fluorescence microscopy in living cells. We found that the N-terminal peptide encompassing amino acids 1 to 32 represents the minimal Golgi-targeting signal sufficient to localize EGFP to the same compartment as the full-length C2GnT. This peptide makes up the cytoplasmic and the transmembrane domains of the enzyme and was referred to as CTd (cytoplasmic and transmembrane domains). We compared the Golgi-targeting efficiency of the C2GnT-derived CTd with its homologous domains from other glycosyltransferases, including the H-type alpha(1,2)-fucosyltransferase (FucTI), the polypeptide N-acetylgalactosaminyltransferase-I (GalNAcT-I), the alpha(1,3)-fucosyltransferase VII (FucTVII), and the alpha(2,6)-sialyltransferase (ST6Gal-I) and found that the Golgi-targeting determinants of these glycosyltransferases were also composed of their cytosolic and transmembrane domains. To investigate whether the CTd of C2GnT could serve as a cis to medial Golgi-specific signal, we tested its ability to mislocalize two late-Golgi acting glycosyltransferases FucTI and FucTVII. We show that fusing the C2GnT-derived CTd with the catalytic domain of FucTVII resulted in a complete mislocalization of the enzyme to the C2GnT compartment, with a parallel alteration of sialyl-Lewis x synthesis and P-selectin binding. The intracellular distribution and activity of FucTI, however, were not affected. Thus, CTds of either early or late-Golgi acting glycosyltransferases represent the Golgi-targeting domains of these enzymes. In addition, we show that C2GnT-derived CTd can function as a cis/medial Golgi-targeting determinant.
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PMID:The cytosolic and transmembrane domains of the beta 1,6 N-acetylglucosaminyltransferase (C2GnT) function as a cis to medial/Golgi-targeting determinant. 1182 83


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