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:2.4.99.6 (sialyltransferase)
1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During studies on the Golgi apparatus immunolocalization of beta-galactoside alpha 2,6-sialyltransferase in intestinal cells, immunostaining of a number of post-Golgi apparatus structures including mucus droplets and plasma membrane were observed. In order to determine if this labeling was in fact due to sialyltransferase and not carbohydrate-specific antibodies in the polyclonal antiserum preparation, fusion protein to sialyltransferase was used to epitope purify polypeptide-specific antibodies. The affinity purification was performed on a column containing a beta-galactosidase-sialyltransferase fusion protein expressed in Escherichia coli. Using such antibodies we present evidence that in intestinal cells sialyltransferase is not only present in the Golgi apparatus cisternal stack but also its transtubular network and various post-Golgi apparatus structures. In absorptive enterocytes, post-Golgi apparatus vesicles, the brush border and basolateral plasma membrane, multivesicular bodies, and lysosome-like structures were labeled. In goblet cells the limiting membrane and lumen of forming and mature mucus droplets as well as the plasma membrane exhibited label for sialyltransferase. The results provide evidence for "ecto-sialyltransferase" in the plasma membranes of these cells, and suggest that most of the sialyltransferase is released from the Golgi membranes and becomes secreted with the goblet cell mucus. In addition, the polypeptide epitope-purified antibody was also used to examine regional expression of sialyltransferase in the rat intestinal epithelium. Immunolabel was restricted to the large intestine and not found in duodenum, jejunum, and ileum. Direct measurement of the enzyme activity was found to correlate with the immunoelectron microscopic data. This observation suggests that there is regional specific expression of the beta-galactoside alpha 2,6-sialyltransferase.
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PMID:Post-Golgi apparatus localization and regional expression of rat intestinal sialyltransferase detected by immunoelectron microscopy with polypeptide epitope-purified antibody. 245 61

In this report we describe the alteration of the N-linked oligosaccharide terminal sequences of Chinese hamster ovary cell glycoproteins by expression of a beta-galactoside alpha 2,6-sialyltransferase cDNA. While wild type cells normally produce sugar chains terminating in the NeuAc alpha 2,3Gal linkage, the expressed enzyme competes with the endogenous sialyltransferase to attach an alternative terminal sequence, NeuAc alpha 2,6Gal. Subcellular localization of the NeuAc alpha 2,6Gal product by lectin-gold electron microscopy revealed localization throughout the Golgi apparatus cis to trans, post-Golgi membranes and vesicular structures. The results demonstrate the potential for purposefully altering terminal carbohydrate structures in vivo by "mis-expressing" terminal glycosyltransferases that compete with the endogenous enzyme normally produced by the cells.
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PMID:Alteration of terminal glycosylation sequences on N-linked oligosaccharides of Chinese hamster ovary cells by expression of beta-galactoside alpha 2,6-sialyltransferase. 266 74

The effect of a single administration and a 6-week treatment with ethanol on rat liver sialyltransferase activity towards asialoglycoproteins and N-acetyllactosamine (Gal beta 1,4GlcNAc) was studied. Since only the alpha 2,6-sialyltransferase is involved in the in vivo sialylation of transferrin, Gal beta 1,4GlcNAc was chosen as an acceptor and alpha 2,6-sialyl-N-acetyllactosamine was separated from the corresponding alpha 2,3-sialyl isomer present in the sialyltransferase reaction mixture by high-performance liquid chromatography. After a single ethanol administration there was a low (about 20%) but significant (p less than 0.005) reduction of sialyltransferase activity towards asialotransferrin as well as a reduced alpha 2,6-sialyltransferase activity towards N-acetyllactosamine. An opposite result was found in the chronically ethanol-treated rats: in these animals either the total or alpha 2,6-sialyltransferase activity was slightly higher than in control animals. Blood ethanol concentration was significantly high (3.3 +/- 1.2 mg/ml) only in the acute-treated animals, suggesting that the accumulation in the body of ethanol and/or its metabolites induces a reduction of liver alpha 2,6-sialyltransferase activity responsible for the transferrin sialylation. Current results are consistent with the finding (Stibler H, Hultcrantz R: Alcohol Clin Exp Res 11:468-473, 1987) that an enhanced level of hyposialylated transferrin isoforms is a marker of present but not previous alcohol abuse.
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PMID:Effect of acute and chronic ethanol administration on rat liver alpha 2,6-sialyltransferase activity responsible for sialylation of serum transferrin. 268 63

The hepatic acute phase response is accompanied by increased levels of Gal beta 1-4GlcNAc alpha 2,6-sialyltransferase activity in liver and in circulation. Previous studies suggested that cytokines and glucocorticoids mediate the induction of this sialyltransferase activity. In this study the regulation of sialyltransferase expression by dexamethasone in H35 rat hepatoma cells is assessed by Northern hybridization and enzyme activity assays. Exposure of H35 cells to 1 microM dexamethasone for 24 h causes a 3-4-fold enrichment of sialyltransferase mRNA and a corresponding increase in enzymatic activity. The induction of sialyltransferase mRNA begins within 3 h of dexamethasone treatment and reaches a plateau within 24 h. Sialyltransferase mRNA induction is dose dependent; the minimum concentration of dexamethasone necessary for induction is 10(-8) M, and induction was maximal at 10(-6) M. Induction is sensitive to actinomycin D, suggesting that regulation may be exerted by altering the rate of mRNA synthesis. Puromycin and cycloheximide are ineffective in blocking induction, suggesting that de novo protein synthesis is not required for induction. Finally, dexamethasone alone is sufficient for maximum induction of sialyltransferase mRNA. In contrast, maximal induction of alpha 1-acid glycoprotein, a well studied hepatic acute phase reactant, requires both dexamethasone and cytokines, implying that different pathways exist for the induction of participants in the acute phase response.
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PMID:Regulation of beta-galactoside alpha 2,6-sialyltransferase gene expression by dexamethasone. 291 88

This report describes the primary structure of a rat liver beta-galactoside alpha 2,6-sialyltransferase (EC 2.4.99.1), a Golgi apparatus enzyme involved in the terminal sialylation of N-linked carbohydrate groups of glycoproteins. The complete amino acid sequence was deduced from the nucleotide sequence of cDNA clones of the enzyme. The primary structure suggests that the topology of the enzyme in the Golgi apparatus consists of a short NH2-terminal cytoplasmic domain, a 17-residue hydrophobic sequence which serves as the membrane anchor and signal sequence, and a large lumenal, catalytic domain. NH2-terminal sequence analysis of a truncated form of the enzyme, obtained by purification from tissue homogenates, reveals that it is missing a 63-residue NH2-terminal peptide which includes the membrane binding domain. These and supporting results show that soluble forms of the sialyltransferase can be generated by proteolytic cleavage between the NH2-terminal signal-anchor and the catalytic domain.
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PMID:Primary structure of beta-galactoside alpha 2,6-sialyltransferase. Conversion of membrane-bound enzyme to soluble forms by cleavage of the NH2-terminal signal anchor. 312 4

Cell surface expressed lactosaminyl glycans were determined on live cells by flow cytometry using a sialyltransferase mediated labeling procedure. Fluorescent CMP-sialic acid and Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase were applied to probe expression of acceptor glycans on untreated or sialidase pretreated erythrocytes. After enzymatic fluorescence labeling, erythrocytes were treated with endo-beta-galactosidase or trypsin to distinguish polylactosaminyl- and complex-type glycans. The expression of lactosaminyl sequences on cord- was 20% lower than on adult cells. After sialidase treatment fluorescence incorporation on both cell types increased twofold compared to untreated cells indicating a low sialylation extent. A recombinant alpha 2,3-sialyltransferase was preferentially labeling polylactosaminyl glycans. Taking advantage of the different fine specificity as determined here, alpha 2,6- and alpha 2,3-sialyltransferase can be applied to distinguish certain types of lactosaminyl glycans.
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PMID:Enzymatic analysis of cell surface lactosaminyl glycans by flow cytometry. 757 5

The synthesis of alpha 2,3-linked sialic acid to Gal(beta 1,3)GalNAc is mediated by at least three beta-galactoside alpha 2,3-sialyltransferases (EC 2.4.99.4, SiaT-4) that are encoded by three distinct genes. In contrast, only a single gene encodes the beta-galactoside alpha 2,6-sialyltransferase (EC 2.4.99.1, SiaT-1). This report assesses the relationship and nature of the SiaT-4 genes. Analysis of human-mouse somatic cell hybrids demonstrates that the sialyltransferase genes are dispersed in the human genome. The gene for SiaT-4 resides in chromosome 8, that for SiaT-4b resides in p21-p34 of chromosome 1 and that for SiaT-4c in q23.3-qter of chromosome 11. The gene symbols for these genes have been designated SIAT4A, SIAT4B and SIAT4C, respectively. To assess the structural organization of one of the SiaT-4 genes, a human SiaT-4a cDNA from submaxillary glands was isolated and characterized. Rapid amplification of cDNA 5' ends (5'-RACE) analysis indicates an unusually long 1 kb 5'-untranslated leader. The catalytic domain of the cloned sequence was expressed in transfected cells and was shown to be competent in mediating the specific synthesis of sialic acid alpha 2,3 to Gal(beta 1,3)GalNAc-R. Genomic sequences for SiaT-4a were also isolated and examined. The data demonstrate that coding information for SiaT-4a protein is dispersed into seven discrete exon segments in a manner reminiscent of the SiaT-1 gene. Furthermore, as in the SiaT-1 gene, intervening sequences interrupt both sialylmotif domains, regions that are conserved among all known sialyltransferases.
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PMID:Three genes that encode human beta-galactoside alpha 2,3-sialyltransferases. Structural analysis and chromosomal mapping studies. 765 69

The human beta-galactoside alpha 2,6-sialyltransferase (EC 2.4.99.1) (SiaT-1) gene is localized to human chromosome 3 (q21-q28) by Southern analysis of somatic cell hybrids and by in situ hybridization of metaphase chromosomes. Comparative analysis between the human and the previously reported rat SiaT-1 genomic sequences demonstrates precise conservation of the intron/exon boundaries throughout the coding domains. Furthermore, there is extensive inter-species sequence similarity in some of the exons that contain information only for the 5'-leader regions. Human genomic sequences were also analyzed to reconcile reported differences in the 5'-untranslated region in SiaT-1 mRNAs. In cultured cell lines of the B-lineage, Reh, Nalm-6, Jok-1, Ball-1, Daudi, and Louckes, the study demonstrates that three upstream exons, Exons(Y+Z) and Exon(X), are mutually exclusively utilized, resulting in at least two distinct populations of SiaT-1 mRNA being synthesized. None of these exons is present in the SiaT-1 mRNA isotype expressed in HepG2 human hepatoma cells. In all B-lymphoblastoid cell lines examined, the basal level SiaT-1 mRNA is maintained by the expression of an isotype containing the Exons(Y+Z) sequence. The slightly smaller SiaT-1 mRNA, which contains the Exon(X) sequence but not Exons(Y+Z) sequence, is synthesized at a high level and found only in Jok-1, Daudi, and Louckes, the cell lines with mature B-cell phenotype. The study also provides further evidence that induced SiaT-1 expression accompanies the appearance of CDw75, a putatively sialylated cell surface epitope and a marker of human mature B-lymphocytes. The SiaT-1 induction is the result of the appearance of a novel form of SiaT-1 mRNA isotype.
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PMID:Chromosome mapping and organization of the human beta-galactoside alpha 2,6-sialyltransferase gene. Differential and cell-type specific usage of upstream exon sequences in B-lymphoblastoid cells. 778 24

All members of the sialyltransferase gene family cloned to date contain a conserved region, the "sialylmotif," consisting of 48-49 amino acids in the center of the coding sequence. To investigate the function of this motif, mutant constructs of the Gal beta 1,4GlcNAc alpha 2,6-sialyltransferase were designed by site-directed mutagenesis, replacing 11 individual conserved amino acids with alanine. Each of the mutants was expressed in COS-1 cells, and eight of these retained sialyltransferase activity, allowing comparison of their enzymatic properties with that of the wild type enzyme. Kinetic analysis showed that six of eight mutants had a 3-12-fold higher Km for the donor substrate CMP-NeuAc relative to the wild type enzyme, while the Km values for the acceptor substrate were within 0.5-1.2-fold of the wild type for all eight mutants evaluated. The Ki of the donor substrate analog CDP was also evaluated for the recombinant sialyltransferase with the Val to Ala mutation at residue 220, which produced a 6-fold increase in Km of CMP-NeuAc. A corresponding increase in Ki of 3.4-fold was observed for CDP, indicating a decreased affinity for the cytidine nucleotide. Taken together, these results suggest that the conserved sialylmotif in the sialyltransferase gene family participates in the binding of the common donor substrate, CMP-NeuAc.
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PMID:The sialyltransferase "sialylmotif" participates in binding the donor substrate CMP-NeuAc. 782 76

A cDNA clone encoding a new type of GalNAc alpha 2,6-sialyltransferase (ST6GalNAc II) with a structure similar to that of a previously cloned GalNAc alpha 2,6-sialyltransferase (ST6GalNAc I; Kurosawa, N., Hamamoto, T., Lee, Y.-C., Nakaoka, T., Kojima, N., and Tsuji, S. (1994) J. Biol. Chem. 269, 1402-1409) was obtained from chicken testes. The predicted amino acid sequence of ST6GalNAc II encodes a protein with type II transmembrane topology, as found for other glycosyltransferases, and showed 32% identity with that of ST6GalNAc I. Transfection of the full length ST6GalNAc II gene into COS cells led to GalNAc alpha 2,6-sialyltransferase activity with a different substrate specificity from that of ST6GalNAc I. Moreover, asialofetuin after treatment with beta-galactosidase did not serve as an acceptor for this enzyme. 14C-Sialylated oligosaccharides obtained from resialylated asialobovine submaxillary mucin with this enzyme were identical to Gal beta 1,3([14C]NeuAc alpha 2,6)GalNAc-ol but not [14C]NeuAc alpha 2,6GalNAc-ol. These results clearly show that the expressed enzyme is a novel type of sialyltransferase that requires beta-galactoside residues linked to GalNAc residues, whereas sialic acid residues linked to galactose residues are not essential for the activity.
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PMID:Cloning and expression of Gal beta 1,3GalNAc-specific GalNAc alpha 2,6-sialyltransferase. 803 63


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