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)

The factors regulating modifications of terminal beta-Gal residues in lactosaminyl (Gal beta 1-->4GlcNAc beta-->R) units in intact glycoproteins are not well understood. To examine these factors, rat liver alpha 2,3 sialyltransferase (alpha 2,3ST) and alpha 2,6 sialyltransferase (alpha 2,6ST) and the murine alpha 1,3 galactosyltransferase (alpha 1,3GT) were incubated with a variety of well-defined desialylated glycoproteins and with glycoproteins in extracts of the Lec2 mutant CHO cells. Lec2 cells constitutively synthesize nonsialylated glycoproteins with terminal lactosaminyl sequences. The results demonstrate that each enzyme displays preferences for glycoprotein acceptors and in the types of N-glycans recognized. The alpha 2,3ST, in contrast to the alpha 2,6ST and alpha 1,3GT, prefers more branched N-glycans compared to diantennary N-glycans. However, only the alpha 1,3GT is able to efficiently modify polylactosamines (3Gal beta 1-->4GlcNAc beta 1-->)n in N-glycans. Glycopeptides were also prepared by proteolysis of Lec2 glycoproteins and tested as acceptors compared to intact Lec2 glycoproteins. The alpha 2,6ST and alpha 1,3GT utilized intact glycoproteins and glycopeptides with a 2-fold preference for the former over the latter. In contrast, the alpha 2,3ST showed a 20-fold preference for intact glycoproteins over glycopeptides. These results demonstrate that each of these terminal glycosyltransferases differentially recognizes glycans and glycoprotein acceptors, and that the alpha 2,3ST requires peptide features for efficient utilization of branched N-glycan acceptors.
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PMID:Differential recognition of glycoprotein acceptors by terminal glycosyltransferases. 913 31

Intracellular glycosyltransferase protein expression can be assessed by flow cytometry. We report the detectability of the Golgi associated beta1,4 galactosyltransferase (GT) and alpha2,6 sialyltransferase (ST) upon permeabilization in Jurkat and EBV-JY cells representing a T- and B-lymphoid cell line, respectively. The method employs fixation with paraformaldehyde and permeabilization with saponin. It ensures reliable internalization of the antibody and little background staining and does not cause leakage of the antigen. We first applied monoclonal antibodies to GT for establishment of this method by flow cytometry. The obtained flow cytometric signal could be localized to the Golgi apparatus by confocal laser scanning microscopy. To exclude interference from possible cell-surface staining, measurements were carried out on non-permeabilized cells. No signal was found in Jurkat cells, while low but measurable ecto-galactosyltransferase was found on EBV-JY cells. F(ab)'2 fragments of polyclonal antisera to GT and ST were generated and shown to be useful for double indirect staining with the monoclonal antibody. The method described here permits relative assessment of Golgi glycosyltransferase expression in lymphoid cells by flow cytometry.
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PMID:Flow cytometric detection of the Golgi apparatus using antibodies to glycosyltransferases. 913 55

Malignant transformation of epithelial cells is associated with abnormal glycosylation of mucins. The aim of this work was to evaluate the changes in the O-glycosylation processes during differentiation of tumor cells by performing in vitro reactions using crude microsomal preparations obtained from a subpopulation of HT-29 cells capable of differentiating into mucin-secreting cells (HT-29 MTX cells). The reactions of O-glycosylation were carried out at different times of culture: before confluence (Day 5), when cells are still undifferentiated, and after confluence (Day 21), when cells display a mucin-secreting phenotype. As acceptor for the UDP-N-acetylgalactosamine:polypeptide Nacetylgalactosaminyltransferase (GalNAc transferase), the peptide motif TTSAPTTS (tandem repeat deduced from MUC5AC human gastric gene, expressed in HT-29 MTX cells) was used. A higher rate of enzyme activity was observed in preconfluent cells, and analysis by capillary electrophoresis and electrospray mass spectrometry showed a different pattern of galactosaminylation in pre- and postconfluent cells. Core 1 UDP-galactose:N-acetyl-alpha-galactosaminyl-R 3-beta-galactosyltransferase (3-beta-galactosyltransferase) activityalso decreased with the differentiation, whereas CMP-neuraminic acid:galactose-beta-1, 3-N-acetyl-alpha-galac- tosaminyl-R 3-alpha-sialyltransferase activity increased. In comparison, the evolving process of mucin biosynthesis was tested by the analysis of purified mucins of HT-29 MTX cells, in amino acid and carbohydrate composition, and immunoreactivity assays using several antibodies and lectins. The results suggested that (i) no mucins were detected at Day 5, while the GalNAc transferase and 3-beta-galactosyltransferase activities were already at high rates; (ii) the mucins purified from postconfluent cells showed a high content of sialic acid in an alpha-2,3-linkage to galactose residues; and (iii) cellular differentiation seemed to be accompanied by more regulated processes of glycosylation. This study of the O-glycosylation in HT-29 MTX cells is thus an interesting approach to analyzing the regulation of mucin biosynthesis during cellular differentiation.
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PMID:O-Glycosylation and cellular differentiation in a subpopulation of mucin-secreting HT-29 cell line. 928 57

Dynactin is a multisubunit complex that plays an accessory role in cytoplasmic dynein function. Overexpression in mammalian cells of one dynactin subunit, dynamitin, disrupts the complex, resulting in dissociation of cytoplasmic dynein from prometaphase kinetochores, with consequent perturbation of mitosis (Echeverri, C.J., B.M. Paschal, K.T. Vaughan, and R.B. Vallee. 1996. J. Cell Biol. 132:617-634). Based on these results, dynactin was proposed to play a role in linking cytoplasmic dynein to kinetochores and, potentially, to membrane organelles. The current study reports on the dynamitin interphase phenotype. In dynamitin-overexpressing cells, early endosomes (labeled with antitransferrin receptor), as well as late endosomes and lysosomes (labeled with anti-lysosome-associated membrane protein-1 [LAMP-1]), were redistributed to the cell periphery. This redistribution was disrupted by nocodazole, implicating an underlying plus end-directed microtubule motor activity. The Golgi stack, monitored using sialyltransferase, galactosyltransferase, and N-acetylglucosaminyltransferase I, was dramatically disrupted into scattered structures that colocalized with components of the intermediate compartment (ERGIC-53 and ERD-2). The disrupted Golgi elements were revealed by EM to represent short stacks similar to those formed by microtubule-depolymerizing agents. Golgi-to-ER traffic of stack markers induced by brefeldin A was not inhibited by dynamitin overexpression. Time-lapse observations of dynamitin-overexpressing cells recovering from brefeldin A treatment revealed that the scattered Golgi elements do not undergo microtubule-based transport as seen in control cells, but rather, remain stationary at or near their ER exit sites. These results indicate that dynactin is specifically required for ongoing centripetal movement of endocytic organelles and components of the intermediate compartment. Results similar to those of dynamitin overexpression were obtained by microinjection with antidynein intermediate chain antibody, consistent with a role for dynactin in mediating interactions of cytoplasmic dynein with specific membrane organelles. These results suggest that dynamitin plays a pivotal role in regulating organelle movement at the level of motor-cargo binding.
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PMID:Overexpression of the dynamitin (p50) subunit of the dynactin complex disrupts dynein-dependent maintenance of membrane organelle distribution. 933 49

Carbohydrates on cell surfaces are important biomolecules in various biological recognition processes. Elucidation of the biological roles of complex oligosaccharides necessitates an efficient methodology to synthesize these compounds and their analogs. Enzymatic synthesis renders itself to be useful in the construction of an oligosaccharide structure owing to its mild reaction condition, high regio- and stereoselectivity. This review article focuses on the recent progress in oligosaccharide syntheses catalyzed by glycosyltransferases, namely sialyltransferase, galactosyltransferase, fucosyltransferase, and N-acetylglucosaminyltransferase. A survey of the latest patent and literature related to this field is also included.
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PMID:Utilization of glycosyltransferases to change oligosaccharide structures. 937 27

Rat serum was found to contain an inhibitor of pure alpha2-6 sialyltransferase (EC 2.4.99.1). The inhibitor was a high Mr protein isolated by molecular filtration on Sephadex G100, followed by anion exchange chromatography on Sephadex DEAE A25, then separation on Sepharose CL 4B, and finally by isoelectric focusing. Electrophoretic separation and subsequent N-terminal sequence analysis of the active inhibitor preparation showed the presence of two protein components, identified as rat C-reactive protein, and rat alpha1 macroglobulin. Pure rat CRP did not inhibit alpha2-6 sialyltransferase. Treatment of the inhibitor preparations with monospecific antibodies against rat alpha1 macroglobulin blocked inhibitory activity in a dose-dependent manner. The results present strong evidence that alpha1 macroglobulin is capable of acting as an inhibitor of alpha2-6 sialyltransferase. No inhibition of galactosyltransferase (EC 2.4.1.38) could be detected, indicating that the interaction with alpha1 macroglobulin may have specificity among the glycosyltransferases. The entrapment of alpha2-6 sialyltransferase by alpha1 macroglobulin presented here occurs in vitro and will require further in vivo investigations to determine the precise physiological significance. Independent of the physiologic significance is the finding that this interaction occurs in vitro, which, pending elucidation of the precise mechanism and specificity, may provide a new tool for investigations into the functional significance of sialylation, and potentially for use or design of new inhibitors of therapeutic value in physiologic conditions involving altered levels of sialylation.
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PMID:Identification of rat alpha1 macroglobulin as an inhibitor of rat Galbeta1-4GlcNAc alpha2-6 sialyltransferase. 937 81

Sialylation is a biosynthetic process occurring in the trans compartments of the Golgi apparatus. Corresponding evidence is based on localization and biochemical studies of alpha2, 6(N)-sialyltransferase (ST6Gal I) as previously reported. Here we describe generation and characterization of polyclonal antibodies to recombinant rat alpha2,3(N)-sialyltransferase (ST3Gal III) expressed as a soluble enzyme in Sf9 cells or as a beta-galactosidase-human-ST3Gal III fusion-protein from E.coli , respectively. These antibodies were used to localize ST3Gal III by immunofluorescence in various cell lines and rat kidney tissue sections. In transiently transfected COS cells the antibodies directed to soluble sialyltransferase or the sialyltransferase portion of the fusion-protein only recognized the recombinant antigen retained in the endoplasmic reticulum. However, an antibody fraction crossreactive with beta-galactosidase recognized natively expressed ST3Gal III which was found to be colocalized with beta1, 4-galactosyltransferase in the Golgi apparatus of several cultured cell lines. Antibodies affinity purified on the beta-galactosidase-ST3Gal III fusion-protein column derived from both antisera have then been used to localize the enzyme in perfusion-fixed rat kidney sections. We found strong staining of the Golgi apparatus of tubular epithelia and a brush-border-associated staining which colocalized with cytochemical staining of the H+ATPase. This subcellular localization was not observed for ST6Gal I which localized to the Golgi apparatus. These data show colocalization in the Golgi apparatus and different post-Golgi distributions of the two sialyltransferases.
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PMID:Immunocytochemical localization of alpha2,3(N)-sialyltransferase (ST3Gal III) in cell lines and rat kidney tissue sections: evidence for golgi and post-golgi localization. 945 Oct 34

IgM are glycoproteins secreted by plasma cells as (mu2L2)5+J or (mu2L2)6 polymers. In most species, mu- and J-chains bear five and one N -glycans, respectively. Here we compare the terminal glycosylation patterns of 4-hydroxy-3-nitrophenylacetyl (NP)-specific IgM secreted by transfectants of the J558L mouse myeloma deficient in the alpha2,6 sialyltransferase [alpha2,6ST(N)] or by a hybridoma expressing this enzyme (B1.8 cells). The absence of alpha2,6-sialylation results in an increased addition of alpha1, 3-galactosyl residues to mu- and J-chain N-glycans. Since alpha1, 3-galactosyltransferase (alpha1,3Gal-T) is similarly expressed in the two cell lines, these results indicate that a competition reaction occurs in vivo between alpha2,6ST(N) and alpha1,3Gal-T. In the alpha2,6ST(N) deficient transfectants, mu-chains lacking the C-subterminal Cys575 residue, which are secreted mainly in the form of mu2L2 monomers, are more efficiently capped by alpha1, 3-galactosyl residues, confirming that polymerization significantly reduces the accessibility of mu-chain glycans to the Golgi processing enzymes involved in the biogenesis of antennary sugars. Functional assays indicate that IgM sialylation affects antigen-binding and complement-dependent hemolysis of haptenated red blood cells.
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PMID:Differential expression of Galalpha1,3Gal epitope in polymeric and monomeric IgM secreted by mouse myeloma cells deficient in alpha2, 6-sialyltransferase. 963 16

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

Sialyl-Lex (sLex) antigen expression recognized by KM93 monoclonal antibody was significantly down-regulated during differentiation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in human pre-B lymphocytic leukemia cell line KM3. The sLex determinants were almost exclusively expressed on O-linked oligosaccharide chains of an O-glycosylated 150-kDa glycoprotein (gp150). A low shear force cell adhesion assay showed that TPA treatment significantly inhibited E-selectin-mediated cell adhesion. Transcript and/or enzyme activity levels of alpha1-->3-fucosyltransferase, alpha2-->3-sialyltransferase, beta1-->4-galactosyltransferase, and elongation beta1-->3-N-acetylglucosaminyltransferase did not correlate with sLex expression levels. However, transcript and enzyme activity levels of core 2 GlcNAc-transferase (C2GnT) were significantly down-regulated during TPA treatment. Following transfection and constitutive expression of full-length exogenous C2GnT transcript, C2GnT enzyme activities were maintained at high levels even after TPA treatment and down-regulation of cell surface sLex antigen expression by TPA was completely abolished. Furthermore, in the transfected cells, the KM93 reactivity of gp150 was not reduced by TPA treatment, and the inhibition of cell adhesion by TPA was also blocked. These results suggest that sLex expression is critically regulated by a single glycosyltransferase, C2GnT, during differentiation of KM3 cells.
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PMID:Single glycosyltransferase, core 2 beta1-->6-N-acetylglucosaminyltransferase, regulates cell surface sialyl-Lex expression level in human pre-B lymphocytic leukemia cell line KM3 treated with phorbolester. 975 22


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