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)

alpha 2,6 sialyltransferase towards the N-acetyllactosaminyl sequence (alpha 2,6 ST, E.C. 2.4.99.1) is one of the major sialyltransferases in human colonic cells; it strongly increases in human colorectal tumors and is largely expressed in fetal and neonatal rat colon. In this study we demonstrate that human colon carcinoma CaCo-2 cells, which differentiate spontaneously into enterocytes when maintained confluent for several days, exhibit a very high expression of alpha 2,6 ST both in the cell-bound and soluble form. When the CaCo-2 cells were cultured on porous membranes the soluble alpha 2,6 ST was mainly detected in the medium collected from the chamber corresponding to the basolateral face of the monolayer. The soluble alpha 2,6 ST could be concentrated and purified from the alpha 2,3 sialyltransferase by affinity chromatography on Blue Sepharose.
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PMID:The expression of soluble and cell-bound alpha 2,6 sialyltransferase in human colonic carcinoma CaCo-2 cells correlates with the degree of enterocytic differentiation. 159 Aug

Human chorionic gonadotrophin (hCG) is a heterodimeric glycoprotein hormone consisting of an alpha- and a beta-subunit, both containing two N-linked, complex-type glycans. Using this hormone as a model glycoprotein, the influence of its polypeptide part on the activity and specificity of bovine colostrum CMP-NeuAc:Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase (alpha 6-sialyltransferase) was investigated. Initial rates of sialic acid incorporation into the desialylated glycans of hCG alpha and hCG beta in the heterodimer were higher with the alpha-subunit. This appeared to be due to a higher V which, together with a slightly lowered affinity (higher Km), resulted in a higher kinetic efficiency of the sialyltransferase for the glycans of this subunit. By contrast, the kinetic parameters did not differ significantly when the subunits were in the free form, indicating that the differences in the kinetics of sialylation found for the subunits in the heterodimeric state were not caused by the differences in N-linked carbohydrate structures of the subunits. It is proposed that these effects are due to conformational constraints which the polypeptide moieties put on the glycan chains upon dimerization. Furthermore, it was investigated whether the polypeptide of hCG would interfere with the sialyltransferase so as to alter the branch specificity of the enzyme. 1H-NMR spectroscopy (400 MHz) of the glycan chains, alpha 6-sialylated in vitro, showed that the enzyme highly prefers the galactosyl residue at the Gal beta 1----4GlcNAc beta 1----2-Man alpha 1----3Man branch for attachment of the first mol of sialic acid into the diantennary glycans of desialylated hCG.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The polypeptide part of human chorionic gonadotrophin affects the kinetics of alpha 6-sialylation of its N-linked glycans but does not alter the branch specificity of CMP-NeuAc:Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase. 160 56

Synthetic sialic acid analogues varying in the substitutents at position C-9 were analyzed for their ability to replace the natural receptor determinant for influenza C virus, N-acetyl-9-O-acetylneuraminic acid (Neu5,9Ac2). By incubation of erythrocytes with sialyltransferase and the CMP-activated analogues, the cell surface was modified to contain sialic acid with one of the following C-9 substituents: an azido, an amino, an acetamido, or a hexanoylamido group. Among these, only 9-acetamido-N-acetylneuraminic acid (9-acetamido-Neu5Ac) was able to function as a receptor determinant for influenza C virus as indicated by the ability of the virus to agglutinate the modified red blood cells. In contrast to the natural receptors, 9-acetamido-Neu5Ac-containing receptors were found to be resistant against the action of sialate 9-O-acetylesterase, the viral receptor-destroying enzyme. No difference in the hemolytic activity of influenza C virus was detected when analyzed with erythrocytes containing either Neu5,9Ac2 or 9-acetamido-Neu5Ac on their surface. This finding indicates that cleavage of the receptor is not required for the viral fusion activity. The sialic acid analogues should be useful for analyzing not only the importance of the receptor-destroying enzyme of influenza C virus, but also other biological processes involving sialic acid.
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PMID:A synthetic sialic acid analogue is recognized by influenza C virus as a receptor determinant but is resistant to the receptor-destroying enzyme. 161 56

The subcellular distribution of polyisoprenyl pyrophosphate phosphatase activity has been examined in rat brain by assaying the release of 32Pi from [beta-32P]dolichyl pyrophosphate (Dol-P-P) as described previously (Scher,M.G. and Waechter, C.J. (1984) J. Biol. Chem., 259, 14580-14585). The highest specific activities of Dol-P-P phosphatase in rat brain were found in the Golgi-enriched light microsomal, synaptic plasma membrane and heavy microsomal fractions. A comparative analysis of the distribution of galactosyltransferase and dolichol kinase reveals that Dol-P-P phosphatase activity co-fractionates with galactosyltransferase activity, and that the high level found in the Golgi-enriched fraction is not due to cross-contamination with heavy microsomes. When beta-labelled C95 Dol-P-P and the C95 allylic polyisoprenyl pyrophosphate (Poly-P-P) were compared as substrates for the Golgi-enriched light microsomal and heavy microsomal fractions, similar Km values were calculated for the two pyrophosphorylated substrates for each membrane fraction. Based on these kinetic analyses, the enzyme(s) catalysing this reaction do not distinguish between substrates containing saturated or allylic alpha-isoprene units. When Dol-P-P phosphatase activity was assessed in submicrosomal fractions obtained from rat liver by two separate procedures, the highest specific activity was also detected in the Golgi-enriched fraction. While the specific activities for Dol-P-P phosphatase and sialyltransferase were in the relative order of Golgi greater than smooth endoplasmic reticulum (ER) greater than rough ER, the relative order of dolichol kinase was rough ER greater than smooth ER greater than Golgi.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Golgi-enriched membrane fractions from rat brain and liver contain long-chain polyisoprenyl pyrophosphate phosphatase activity. 166 43

To establish the basis for the reduced expression of the X determinant on leukemic blasts and the changes in antigenic expression that occur during myeloid maturation, the presence on myeloid cells of X and related structures was examined in conjunction with studies on the activities of the glycosyltransferases involved in their biosynthesis. Expression of X and sialyl-X was weak on blasts in comparison with neutrophils despite the presence of the requisite precursor structures. Much higher levels of 3-fucosyltransferase activity were found in blasts than in neutrophils when nonsialylated substrates were used, but, whereas the enzyme in neutrophils reacted equally well with 3'-sialylated and nonsialylated acceptors, the enzyme in blasts showed a marked preference for nonsialylated substrates. 6'-Sialyltransferase activity was strong in blasts but was not detectable in neutrophils, whereas a much lower level of 3'-sialyltransferase activity was present in both blasts and neutrophils. Dimethyl sulfoxide-induced maturation of HL60 cells was associated with (1) a decrease in both 6'-sialyltransferase and 3-fucosyltransferase activities, (2) a change in the substrate specificity of 3-fucosyltransferase towards that found in mature cells, and (3) increased cell surface expression of sialyl-X. These results suggest that the reduced expression of X in myeloblasts is related to the presence of the strong 6'-sialyltransferase, which uses the precursor substrate at the expense of the 3-fucosyltransferase and prevents the synthesis of X and sialyl-X. The developmental regulation of the levels of 3'- and 6'-sialyltransferases, and the level and specificity of the 3-fucosyltransferases, therefore controls the expression of X and its degree of sialylation.
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PMID:Enzymic control of the expression of the X determinant (CD15) in human myeloid cells during maturation: the regulatory role of 6-sialytransferase. 167 56

Glycosyltransferase activities of highly purified fractions of Golgi apparatus, plasma membrane and endoplasmic reticulum, all from the same homogenates, were analyzed and compared. Additionally, Golgi apparatus were unstacked and the individual cisternae separated into fractions enriched in cis, median and trans elements using the technique of preparative free-flow electrophoresis. Golgi apparatus from both liver and hepatomas were enriched in all glycosyltransferases compared to endoplasmic reticulum and plasma membranes. However, Golgi apparatus from hepatomas showed both elevated fucosyltransferase and galactosyltransferase activities but reduced sialyltransferase and dipeptidyl peptidase IV (DPP IV) activities compared to liver. Activity of N-acetylglucosaminyltransferase was approximately the same in both liver and hepatoma Golgi apparatus. With normal liver, sialyl- and galactosyltransferase activities and DPP IV showed a marked cis-to-trans gradient of activity. Fucosyltransferase was concentrated in two regions of the electrophoretic separations, one corresponding to cis cisternae and one corresponding to trans cisternae. N-Acetylglucosaminyltransferase activity was more widely distributed but the endogenous acceptor activity was predominantly cis. With hepatoma Golgi apparatus, the pattern for DPP IV was similar to that for liver but those of sialyl- and galactosyltransferases differed markedly from liver. Instead of activity increasing cis to trans, the activities for sialyl- and galactosyltransferases decreased. For fucosyltransferases, activity dependent on exogenous acceptor was medial whereas with endogenous acceptor, two activity peaks, cis and trans, still were observed. For N-acetylglucosaminyltransferase the pattern for hepatoma was similar to that for liver. The results indicate alterations in the distribution of glycosyltransferase activities within the Golgi apparatus in hepatotumorigenesis that may reflect altered cell surface glycosylation patterns.
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PMID:Distribution of glycosyltransferases among Golgi apparatus subfractions from liver and hepatomas of the rat. 168 14

After growth of gonococci in the presence of cytidine monophospho-N-acetyl-neuraminic acid (CMP-NANA), their 4.5-kD lipooligosaccharide (LOS) component was increased by approximately 400 daltons, whereas the LOS of strains lacking the 4.5-kD component were unaffected. Expression of mAb-defined epitopes on the 4.5-kD component was decreased on LOS of strains grown in CMP-NANA, and treatment of the LOS with neuraminidase reversed this affect. Gonococci incubated with human PMNs also had decreased expression of the 4.5-kD+ epitopes. A detergent extract of gonococci incorporated radiolabeled NANA in the LOS, suggesting the presence of a sialyltransferase in gonococci. Exogenous sialyltransferases also could use LOS as an acceptor.
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PMID:In vitro and in vivo modification of Neisseria gonorrhoeae lipooligosaccharide epitope structure by sialylation. 169 81

The gangliosides of human hepatoma biopsies, human hepatoma cell lines, and diethylnitrosamine-induced rat hepatomas were examined. These malignant tissues all expressed increased content of disialolactosylceramide (GD3) with respect to their normal counterparts. During the induction of rat hepatoma by diethylnitrosamine, an increase in GD3 levels appeared as early as 12 wk after initiation of diethylnitrosamine, concurrent with the appearance of precancerous hepatocytes. GD3 levels gradually increased to a peak of 4 times that of normal rat liver at 20 wk. CMP-NeuAc:GM3 sialyltransferase, the enzyme that synthesizes GD3 by transfer of sialic acid to GM3, also had tumor-associated elevation during the course of diethylnitrosamine-induction of rat hepatomas. To investigate the relationship of oncogene transformation and changes in ganglioside biosynthesis, NIH 3T3 cells transfected DNAs from human hepatoma or nasopharyngeal carcinoma were studied. The transfectants each expressed the same ganglioside composition, including a detectable level of GD3, as well as enhanced activity of CMP-NeuAc:GM3 sialyltransferase. A correlation between the tumor DNA transfection and the augmentation of GD3 in malignant cells is discussed. Because of the early appearance of GD3 in hepatoma and its possible relationship to oncogene activation, GD3 may be a potentially useful early tumor marker.
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PMID:Enhanced expression of ganglioside GD3 in human and rat hepatocellular carcinoma cells and NIH 3T3 cells transfected with human tumor DNAs. 170 52

Functional maturation of B lymphocytes correlates with expression of the B lineage-specific cell surface glycoprotein CD22. Two CD22 polypeptides have been characterized and suggested to play a role in B cell-B cell interaction as well as in B cell adhesion to monocytes. In this work we provide evidence that CD22 is directly involved in the cognate interaction between B and T cells. One of the two CD22 polypeptides, CD22 beta, interacts with a specific ligand on a subpopulation of CD4+ T cells. Our results suggest that the T cell ligand of CD22 is CD45RO, an isoform of the leukocyte common antigen class of phosphotyrosine phosphatases associated with the helper T cell phenotype. We further demonstrate that CD22 recognizes a second ligand, CD75, expressed predominantly on activated B cells and shown to be a cell surface alpha 2-6 sialyltransferase.
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PMID:The B lymphocyte adhesion molecule CD22 interacts with leukocyte common antigen CD45RO on T cells and alpha 2-6 sialyltransferase, CD75, on B cells. 154 99

Previous studies have shown that purified mitochondrial outer membrane is able to catalyze the transfer of sialic acid from CMP-Neu5Ac to an exogenous asialoglycoprotein acceptor, asialofetuin. Considering the heterogeneity of the glycan chains borne by this glycoprotein, an investigation of mitochondrial sialyltransferase activities was undertaken. Our data provide evidence for the existence of two distinct sialyltransferases in purified mitochondrial outer membranes. The use of different acceptor substrates, the temperature dependence of these enzymes, and their different sensitivity towards a sulfhydryl reagent, p-CMB, allowed us to discriminate between a galactoside alpha(2-3) sialyltransferase and a galactoside alpha(2-6) sialyltransferase presumably involved in the sialylation of O- and N-glycan chains of glycoprotein, respectively. These results are discussed in terms of mitochondrial autonomy for post-translational events.
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PMID:Sialylation processes in mitochondria: evidence for two distinct sialyltransferases located in the outer membrane. 172 30


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