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)

Cell surface carbohydrates have been shown to be altered during cellular differentiation. Alveolar type II (ATII) cells in culture gradually lose their differentiated phenotype. Therefore, the aim of this study was: (1) to characterize changes in terminal carbohydrates of cell surface glycoproteins of rat ATII cells cultured for 1 to 5 days on plastic, and (2) to assess the concomitant changes in sialidase and sialyltransferase activity of ATII cell homogenates. Cells were surface-labeled with potassium-[3H]-borohydride after oxidation by sodium periodate at millimolar concentrations, galactose oxidase or neuraminidase plus galactose oxidase, allowing for the specific labeling of terminal sialic acids, terminal galactose/N-acetylgalactosamine (Gal/GalNAc), or terminal an penultimate Gal/GalNAc residues, respectively. Glycoproteins were separated by SDS-PAGE. On day 1, cells were heavily coated with sialic acids, since no labeling could be introduced with galactose oxidase alone. From day 1 to day 5, we observed a selective and progressive desialylation of two glycoproteins (200 and 165 kD). At the same time, the ATII cells' sialidase activity (pH 4.2) exhibited an 8-fold increase (60.3 +/- 4.0 pmol/min/mg protein on day 1 versus 406.9 +/- 3.7 pmol/min/mg protein on day 5), whereas the sialyltransferase activity increased 2-fold (212 +/- 8 fmol/min/mg protein on day 1 versus 395 +/- 82 fmol/min/mg protein on day 5) and the supernatant sialidase activity was unchanged (2.8 +/- 0.7 pmol/min/ml on day 5). Thus, the phenotypic changes of ATII cells in primary culture are accompanied by a partial cell surface desialylation and an increase in intracellular sialidase activity.
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PMID:Cell surface carbohydrates of rat alveolar type II cells in primary culture. 842 6

Addition of sialic acid residues in the human pathogen Trypanosoma cruzi glycoconjugates is mediated by a trans-sialidase and not by a CMP-sialic acid:glycoconjugate sialyltransferase. Incubation of trans-sialidase with N-[galactose-14C]acetyllactosamine and O-linked oligosaccharides, N-linked glycopeptides (both obtained from fetuin) or sialyllactose showed that the last three compounds were donors of sialic acid residues to the first one. Moreover, N- and O-linked oligosaccharides in asialofetuin and asialomucin, respectively, served as acceptors of sialic acid units. Gangliosides GM3, GD1a and GT1b but not GM2, GM1a nor GD1b donated sialic acid units to N-acetyllactos amine when incubated with trans-sialidase. This showed that only sialic acid units bound to terminal galactosyl residues were transferred. GM1a was converted to GD1a, and GD1b to GT1b when incubated with the appropriate donor. The fact that asialo-GM1a was converted to a ganglioside migrating as GD1a on thin-layer chromatography suggested that sialic acid units may be transferred to internal galactosyl residues, although once linked to those residues they can not be further transferred to other glycoconjugates. Sialic acid residues linked alpha 2,3- but not alpha 2,6- or alpha 2,8- were transferred by the trans-sialidase. Methyl beta-galactoside but not methyl alpha-galactoside served as acceptor of sialic acid units, thus suggesting that terminal alpha-linked galactosyl units in T. cruzi and mammalian glycoproteins are not sialylated by the enzyme. As the trans-sialidase employed in these experiments has been shown to be located on the external surface of the parasite and to be shed to the medium, the relatively broad specificity shown by the enzyme with respect to protein- and lipid-linked oligosaccharides strongly suggests that infection by T. cruzi might alter the sialic acid distribution in glycoproteins and glycolipids of the mammalian host.
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PMID:The action of Trypanosoma cruzi trans-sialidase on glycolipids and glycoproteins. 847 49

Anti-Pr agglutinins (CAs) with the subspecificities anti-Pr1h, -Pr1d, -Pr2, -Pr3h, -Pr3d, -PrM and anti-Sa CAs recognize immunodominant N-acetylneuraminic acid (NeuN Ac) groups of tetra and/or trisaccharides (O-glycans) of glycophorin. These O-glycans are sialylated in alpha 2,3- and/or alpha 2,6-linkages. Sa and most Pr antigens have been inactivated by alpha 2,3-specific sialidases. Antigenicity was reconstituted on desialylated glycophorin by alpha 2,3-specific Gal beta 1,3GalN Ac-sialyltransferase indicating that alpha 2,3-linked NeuN Ac groups are the immunodominant components of Sa and most Pr antigens. Some Pr antigens were resistant to alpha 2,3-specific sialidase and were not reconstituted by alpha 2,3-specific Gal beta 1,3GalN Ac-sialyltransferase, which indicates that alpha 2,6-linked NeuN Ac group represents an immunodominant component of some Pr antigens.
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PMID:Anti-Pr cold agglutinins recognize immunodominant alpha 2,3- or alpha 2,6-sialyl groups on glycophorins. 859 64

Sialyltransferase activities, SAT-3 (CMP-NeuAc:nLcOse4Cer alpha 2-3sialyltransferase) and SAT-4 (CMP-NeuAc:GgOse4Cer alpha 2-3sialyltransferase), in Colo 205 cells catalyze the transfer of sialic acid to the terminal galactose of GlcNc-- and GalNAc-containing glycolipid substrates, respectively. Competition kinetic studies with nLcOse4Cer and GM1 as substrates in a sialyltransferase assay show that these two activities are catalyzed by two different catalytic entities. The two enzymes were co-solubilized with taurochlorate and resolved by DEAE--Cibacron Blue--Sepharose column chromatography into two elution peaks. The column eluent with SAT-3 activity failed to transfer sialic acid to asialo alpha(1)-acid glycoprotein, indicating that this enzyme is different from the sialyltransferase (ST3N) that synthesizes NeuAc alpha 2-3Gal linkage in asparagine-linked oligosaccharides of glycoprotein. However, SAT-3 activity can be immunoprecipitated with a polyclonal antibody produced against a protein expressed in Escherichia coli as GST-fusion protein from an ECB cDNA homolog of an alpha 2-3 sialyltransferase SAT-3 or STZ) the has been cloned from human melanoma cell and human placenta. Thus a concentration-dependent decrease in the residual SAT-3 activity relative to SAT-4 activity was observed in the supernatant after precipitation of the immune complex. Expression of SAT-3 (STZ) cDNA was also detected in Colo 205 cell by RT-PCR, followed by sequence analysis of the RT-PCR product. Characterization of the catalytic reaction products of SAT-3 and SAT-4 with thin-layer chromatography, sialidase treatment, and binding to specific antibodies indicates that both SAT-3 and SAT-4 catalyze the formation of alpha 2-3 linkage between sialic acid and terminal galactose of glycolipid substrates.
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PMID:Characterization of two glycolipid: alpha 2-3sialyltransferases, SAT-3 (CMP-NeuAc:nLcOse4Cer alpha 2-3sialyltransferase) and SAT-4 (CMP-NeuAc:GgOse4Cer alpha 2-3sialyltransferase), from human colon carcinoma (Colo 205) cell line. 861

Interactions between selectins and their oligosaccharide-decorated ligands play a crucial role in the initiation of leukocyte extravasation. We have shown that synthetic multivalent sialyl Lewis x glycans inhibit strongly the adhesion of lymphocytes to endothelium at sites of inflammation. However, enzyme-assisted synthesis of these oligosaccharides si hampered by the lack of sufficient amounts of specific glycosyltransferases. We report here the construction of Saccharomyces cerevisiae strains expressing the soluble catalytic ectodomain of rat Gal(beta)1-3/4GlcNac alpha 2,3-sialyltransferase (ST3Ne) fused to the C-terminus of the hsp150 delta-carrier polypeptide. The hsp150 delta-carrier, which is an N-terminal fragmented of a natural secretory protein of yeast, is able to confer secretion-competence to several heterologous proteins, which otherwise remain in the yeast endoplasmic reticulum. The ST3Ne portion of the hsp 150 delta-ST3Ne fusion protein adopted an enzymatically active conformation and was N-glycosylated and disulfide-bonded. Hsp150 delta-ST3Ne was secreted with a half-time of about 7.5 min and remained intercalated in the cell wall, which covers the yeast plasma membrane. About 110 mU of sialyltransferase per litre was produced in 16 h. Whole live yeast cells were able to transfer sialic acid from CMP-NeuNAc to N-acetyllactosamine yielding alpha 2,3-sialyl-N-acetyllactosamine, as evidenced by paper chromatography, cleavage by linkage-specific sialidase, and NMR analysis. Our data suggest that yeast cells externalizing mammalian glycosyltransferases with the aid of the hsp150 delta-carrier could provide a source of enzymes for synthesis of valuable oligosaccharides.
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PMID:Targeting of active rat alpha 2,3-sialyltransferase to the yeast cell wall by the aid of the hsp 150 delta-carrier: toward synthesis of sLe(x)-decorated L-selectin ligands. 902 48

Of the increasing number of sialidases found to be made by microorganisms, the trypanosome trans-sialidase is unique in its added ability to efficiently carry out a sialyltransferase reaction using preformed glycoconjugates. The enzyme is predicted to have a multidomain structure, with one domain containing sequence and expected structural features found in bacterial sialidases. The trans-sialidase is very similar in overall sequence to another trypanosome enzyme that has only sialidase activity. Hybrid expression constructs containing pieces of these trypanosome trans-sialidase and sialidase genes were used to determine which regions of trans-sialidase are required for sialyltransferase activity. Two domains were found to influence the enzymatic activity: the N-terminal catalytic domain, and a downstream domain that resembles an Fn3-like module.
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PMID:Directed mutagenesis of the Trypanosoma cruzi trans-sialidase enzyme identifies two domains involved in its sialyltransferase activity. 914 54

In search of substrate analogues for the porcine liver beta-D-Gal p-(1-->3)-D-Gal p-NAc: CMP-Neu5Ac-(2-->3')-alpha-sialyltransferase, three disaccharides beta-D-Gal p-(1-->3)-beta-D-Gal p-O-CH3 (5), beta-D-Gal p-(1-->3)-beta-D-(2-OAc)-Gal p-O-CH3 (7) and beta-D-Gal p-(1-->3)-beta-D-(2-OAc)-Gal p-O-Bn (11) were synthesized and tested with the enzyme. Disaccharide 7 turned out to be a very good substrate allowing a rapid access to the trisaccharide alpha-Neu5Ac-(2-->3)-beta-D-Gal p-(1-->3)-beta-D-(2-OAc)-Gal p-O-CH3 (13) on a preparative scale using the crude enzyme immobilized on cationic exchanger. Trisaccharide 13 was further exploited, first as a sialyl donor in Trypanosoma cruzi trans-sialidase catalyzed reaction and second through acetolysis reaction as a source for the synthon alpha-Neu5Ac-(2-->3)-D-Gal (16).
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PMID:Porcine liver (2-->3)-alpha-sialyltransferase: substrate specificity studies and application of the immobilized enzyme to the synthesis of various sialylated oligosaccharide sequences. 920 41

To clarify the relation between the mechanism of apoptosis in tumor tissues and sialic acids on the termini of sugar chains of glycoconjugates, a case of squamous cell carcinoma was examined using immunohistochemistry and glycohistochemistry. Immunohistochemistry and in situ hybridization histochemistry suggested that sialylation by the sialyltransferase in dominant in tumor cells, whereas hydrolysis of sialic acids by the sialidase is dominant in apoptotic bodies. Lectin histochemistry revealed that sialic acid alpha 2, 3 galactose beta 1, 3 N-acetylgalactosamine (Gal beta 1, 3 GalNAc) is present on the surfaces of tumor cells, and Gal beta 1, 3 GalNAc is present on those of apoptotic bodies. The exposed Gal beta 1, 3 GalNAc owing to the decrease in sialic acids on the surfaces of apoptotic bodies may be recognized by the C-type lectin on the macrophage for phagocytosis.
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PMID:[Glycohistochemical analysis of apoptotic bodies in eyelid tumor]. 925 24

Oncogenic transformation is often accompanied by alterations of glycosylation on a tumor cell's surface, which may contribute to uncontrolled cell growth. The sialoglycans and degree of sialylation on the cell surface are of increasing interest because of their possible role in metastasis and tissue invasion. Since primary tumors and metastases may differ in the degree of sialylation, we examined the expression of sialic acid as a terminal constituent of lactosaminyl glycans on the cell surfaces of 30 cervical lymph-node metastases and 30 squamous-cell carcinomas of the oropharynx and oral cavity. Cell-surface sialylation was determined by a new histobiochemical assay on cryostat sections and was based on the enzymatic introduction of a fluorescence-labelled sialic acid into lactosaminyl type (Gal-beta 1-4 GlcNAc) oligosaccharide chains of cell-surface-expressed glycoproteins. To this end, tissues were incubated in the presence of 5-acetamido-9-deoxy-9-fluoresceinyl-thioureido neuraminic acid (CMP-9-fluoresceinyl-NeuAc) and alpha-2,6-sialyltransferase. In order to compare the degree of sialylation with the potential total amount of sialylation sites, pretreatment with sialidase for desialylation was required. We observed a significantly higher amount of lactosaminyl-type binding sites for sialic acid on metastases compared to the primary tumors (P = 0.001), indicating a lower degree of sialylation in metastases. In primary tumors no correlation was seen between the amount of binding sites and tumor localization, TNM stage or histologic grading. Pretreatment of specimens with sialidase demonstrated a significant degree of sialylation on both primary tumors and lymph-node metastases, but no difference between primary tumors and metastases. When tumor stroma of primary tumors and metastases was compared, tumor cells showed a higher degree of free binding sites for sialic acid, but a low degree of sialylation. Our results suggest that differences in the degree of sialylation of glycoconjugates on a tumor cell's surface may play an important role in the process of cell metastasis. Our histobiochemical method turned out to be very reliable, effective and readily performed.
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PMID:A new histobiochemical method to analyze sialylation on cell-surface glycoproteins of head and neck squamous-cell carcinomas. 943 13

Sialidases are hydrolytic enzymes present from virus to higher eukaryotes, catalyzing the removal of sialic acid from glycoconjugates. Some protozoa Trypanosomatidae secrete high levels of sialidase into the medium. We have now purified the secreted sialidase from Trypanosoma rangeli. Its N-terminal sequence reveals 100% identity with the corresponding region of the trans-sialidase from T. cruzi. Trans-sialidase, although homologous to viral and bacterial sialidases, displays a novel sialyltransferase activity and is involved in host cell invasion. Several homologous transsialidase-like genes were cloned from genomic DNA of T. rangeli, and grouped in three subfamilies. Active sialidase-encoding genes were found in one of them. The recombinant sialidase shows similar properties to those of the native enzyme, including undetectable trans-sialidase activity. Nevertheless, it has an overall identity of 68.9% with the catalytic domain of T. cruzi trans-sialidase, increasing to 86.7% admitting conservative substitutions. Only three other eukaryotic sialidases have been previously cloned, none of them showing significant homology to trans-sialidase. The isolation of a highly similar sialidase is relevant to further identify the molecular determinants allowing trans-sialidase activity. As a first approach, chimeric constructs between sialidase and trans-sialidase were generated, one of them rendering a sialidase with three times lower Km than the natural enzyme.
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PMID:Trypanosoma rangeli sialidase: cloning, expression and similarity to T. cruzi trans-sialidase. 945 17


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