Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.99.7 (sialyltransferase)
 1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Our previously described immunoadsorption method for the isolation of vesicles containing the insulin-responsive intracellular glucose transporters from 3T3-L1 adipocytes has been improved in two ways. First, the minimal number of g minutes required to sediment the plasma membranes from the cell homogenate has been determined and, as a result, the supernatant used for immunoadsorption in the new procedure contained twice as much of the intracellular transporters. Second, the immunoadsorption has been performed with affinity-purified antibodies directed against the carboxy terminal peptide of the transporter, rather than against the entire protein. 10(7) cells (10 mg protein) yielded about 12 micrograms of vesicular protein and 11 micrograms of vesicular phospholipid. The transporter constituted 3% of the protein in the vesicles; this amount equates to approx. eight copies of the transporter per 50 nm vesicle. The polypeptide composition of the vesicles was determined by gel electrophoresis and protein staining. Major components, other than the glucose transporter, are polypeptides of Mr 270,000, 245,000, 165,000 and 115,000. The vesicles contained several phosphoproteins; the major ones have a Mr of 245,000, 190,000, 115,000 and 25,000. Insulin treatment of adipocytes did not significantly change the phosphoprotein composition of the vesicles. The vesicles were not enriched in the Golgi marker enzyme, galactosyltransferase. The cellular content of the marker for the trans-Golgi reticulum, sialyltransferase, was too low to detect.
 ...
PMID:Characterization of vesicles containing insulin-responsive intracellular glucose transporters isolated from 3T3-L1 adipocytes by an improved procedure. 304 18

The postnatal development of skeletal muscle is characterized by changes in membrane function associated with N-linked glycoproteins. In the present study, early reactions involved in the synthesis of the dolichol-linked core oligosaccharide were examined in neonatal and adult rabbit skeletal muscle sarcoplasmic reticulum membranes. The initial rate of N-acetylglucosamine incorporation in the presence of exogenous dolichol phosphate was similar between neonate and adult (3.5-4.1 pmol of GlcNAc/min/mg). The Km values for UDP-GlcNAc and exogenous dolichol phosphate were similar. Tunicamycin (0.04-0.08 micrograms/ml) inhibited N-acetylglucosamine incorporation by 50%. UDP-GlcNAc pyrophosphatase activity was greater in neonatal membranes than adult (840 versus 350 pmol of GlcNAc-1-P/min/mg), explaining, in part, the greater enhancement of neonatal GlcNAc incorporation by pyrophosphatase inhibitors. Nucleotide-sugar pyrophosphatase inhibitors (alpha, beta-methylene ATP and dimercaptopropanol) increased the capacity of neonatal activity 4-fold and adult enzyme 2-fold. Analysis of dolichol-linked products by mild acid hydrolysis however, revealed that neonate had higher capacity for N,N'-diacetylchitobiosyl(pyro)phosphoryldolichol synthesis than adult. Mannosyltransferase and glucosyltransferase were elevated 6- and 5-fold in neonate compared to adult membranes. Neonate exhibited 4-fold greater GDP-Man pyrophosphatase activity than adult (500 versus 125 pmol of Man-1-P/min/mg). The Km for GDP-Man increased in the presence of exogenous dolichol phosphate. Increasing concentrations of exogenous dolichol phosphate did not equalize neonate and adult mannosyltransferase activity, indicating that the decline in activity during development was not due to a decrease in a pool of dolichol phosphate accessible to mannosyltransferase. Glucosyltransferase for the synthesis of glucosylphosphoryldolichol was also elevated 5-fold in neonatal compared to adult sarcoplasmic reticulum (7 versus 1.4 pmol of Glc/min/mg). In a previous study, it was reported that glycoprotein sialyltransferase activity decreased by a factor of 6.5 during the postnatal maturation and that total membrane hexose content of sarcoplasmic reticulum decreased by a factor of 8. Together, these results suggest that the postnatal development of skeletal muscle is characterized by coordinated changes in the expression of enzymes involved in both the "early" and "late" reactions of N-linked oligosaccharide biosynthesis.
 ...
PMID:Formation of dolichol-linked sugar intermediates during the postnatal development of skeletal muscle. 631 23

We have assayed glycosyltransferase activities during the granulocytic and macrophage-like differentiation of human promyelocytic leukemia (HL-60) cells. Functional granulocytic differentiation was assayed by the decarboxylation of 2-deoxyglucose in addition to nitroblue tetrazolium reduction. Dimethylsulfoxide (DMSO) treated HL-60 cells, induced to granulocytic differentiation, had higher 2-deoxy-glucose decarboxylation activity, and contained less sialyltransferase (ST), more fucosyltransferase (FT), and more N-acetylglucosaminyltransferase (NGT) activities than untreated cells. HL-60 cells treated with another granulocytic differentiator, retinoic acid, also had higher 2-deoxyglucose decarboxylation activity, and contained less ST, more FT, and more NGT activities than untreated cells. In contrast, cells treated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) reported to differentiate HL-60 to macrophage-like cells, but did not show an increased level of 2-deoxyglucose decarboxylation activity, but contained more galactosyltransferase (GT) and FT activities as compared to untreated cells. These findings suggest that the alterations of glycosyltransferase levels during the differentiation of precursor cells may not depend upon different inducers, but are characteristic of the phenotypic expression of the mature cell type.
 ...
PMID:Glycosyltransferase alterations are cell type related when human promyelocytic leukemia (HL-60) cells are treated with various inducers of differentiation. 641 38

The correlation between levels of sialic acid and sialic acid-containing glycolipids (gangliosides) in tumors and serum with the growth characteristics of the tumors was investigated in transplantable hepatomas and squamous cell carcinomas initiated with the carcinogen N-2-fluorenylacetamide and propagated in vivo and in tissue culture. Tumor lines varied in histologic classification, growth rate, and ability to form pulmonary metastases. There was neither a correlation between growth rate and histologic classification nor between either of these two parameters and the ability to metastasize. Total and ganglioside sialic acid levels were elevated in carcinogen-treated liver and in transplantable hepatomas when contrasted with normal liver. Levels of sialic acid showed a weak correlation with the growth rate of hepatomas. Gangliosides from nonmetastatic hepatoma lines exhibited less N-acetylneuraminic acid--galactose--glucose-N--acylsphingosine (GM3) and an increased ratio of total monosialogangliosides to disialogangliosides than did metastatic lines. Ganglioside patterns of metastatic hepatoma lines more closely resembled the ganglioside patterns of normal liver than did those of the nonmetastatic lines. Concomitant elevations of total and ganglioside sialic acid levels were observed in sera of animals bearing subcutaneous implants. Serum levels of total sialic acid did correlate with total sialic acid levels found in the tumor tissues. The levels of serum sialic acid were not correlated directly with levels of serum sialyltransferase activity. Elevations of both tissue and serum ganglioside sialic acid were consistent features of liver tumorigenesis in the rat after N-2-fluorenylacetamide administration. They appeared, furthermore, to be early events not directly related to tumor cell differentiation or metastasis.
 ...
PMID:Characteristics of transplantable tumors induced in the rat by N-2-fluorenylacetamide: elevations in tissue and serum sialic acid. 692 77

Trypanosomatid protozoa are parasites of considerable medical and economic importance in developing countries. The pathway leading to N-glycosylation in these microorganisms is characterized by the following features: (i) dolichols are composed of only 10-13 isoprene units; (ii) oligosaccharides transferred in N-glycosylation have the compositions Man(6,7,9)GlcNAc2, depending on the species; (iii) trypanosomatids are unable to synthesize dolichol-P-Glc and, in addition, some species lack certain dolichol-P-Man-dependent mannosyltransferases; (iv) the oligosaccharyltransferase does not require the presence of glucose units in the oligosaccharide in order to catalyse an efficient transfer reaction; (v) trypanosomatids have a glucosidase II-like enzyme, but lack glucosidase I; (vi) glucosidase II is required for deglucosylation of oligosaccharides glucosylated by the UDP-Glc:glycoprotein glucosyltransferase, an activity first detected in those parasites; (vii) the structures of polymannose-type compounds in these protozoa have no significant differences with those of their mammalian counterparts except for the presence, in certain species, of oligosaccharides having galactofuranose units linked to external mannose residues; (viii) biantennary complex-type oligosaccharides having in some cases terminal alpha-linked galactose units or poly-N-acetylactosamine extensions, but lacking sialic acid units, have been described in Trypanosoma brucei; (ix) complex-type oligosaccharides having alpha-linked galactose, fucose and sialic acid residues have been described in Trypanosoma cruzi. In this parasite, addition of sialic acid units to glycoproteins and glycolipids is mediated by a trans-sialidase located on the external surface of the parasite and not by an intracellular CMP-sialic acid-dependent sialyltransferase.
 ...
PMID:N-glycosylation in trypanosomatid protozoa. 835 46

Strain F62 of Neisseria gonorrhoeae gonococci (GC) is sensitive to normal human serum unless CMP-N-acetylneuraminic acid (CMP-NANA) is present. NANA is transferred primarily to a 4.5-kDa lipooligosaccharide (LOS) structure by a GC sialyltransferase (Stase). We investigated LOS and Stase expression and serum resistance in strain F62 grown in different carbon sources and growth conditions. Pyruvate-grown GC expressed 1.9- to 5.6-fold more Stase activity than did glucose-grown GC, whereas lactate-grown GC generally expressed intermediate Stase activities. Broth-grown GC expressed two- to fourfold more Stase activity than did plate-grown GC in all carbon sources. Pyruvate- or lactate-grown GC expressed significantly more of the sialylateable 4.5-kDa LOS species than did glucose-grown GC. Anaerobically, the 4.5-kDa LOS species was expressed in greater quantity than the 4.9-kDa N-acetyl galactosamine-terminating species in all carbon sources. Pyruvate-grown GC also incorporated up to threefold more radiolabelled CMP-NANA onto the 4.5-kDa LOS species than did glucose-grown GC. In serum resistance studies, pyruvate-grown GC were 6.5- to 16.1-fold more serum resistant than glucose-grown GC at limiting CMP-NANA concentrations (1.56 to 12.50 microg/ml). Taken together, these results indicate that gonococcal expression of Stase activity is up-regulated by growth in pyruvate or lactate, which correlates with enhanced expression of the sialylateable 4.5-kDa LOS and, for growth in pyruvate, correlates with enhanced sialylation of gonococcal LOS and greater serum resistance. In different in vivo niches, gonococcal LOS sialylation, serum resistance, and interaction with host cells can be highly regulated.
 ...
PMID:Regulation of gonococcal sialyltransferase, lipooligosaccharide, and serum resistance by glucose, pyruvate, and lactate. 889 Feb 17

To investigate the potential of filamentous fungi to synthesize N-glycans that are convertible to a mammalian type, in vitro glycosylation assays were performed. Recombinant human N-acetylglucosaminyltransferase I, human beta-1,4-galactosyltransferase and rat alpha-2,6-sialyltransferase were successively used to mimic part of the mammalian glycosylation synthesis pathway. High-mannose carbohydrates on Trichoderma reesei cellobiohydrolase I were converted to a hybrid mammalian-type structure. Successful modification varied markedly with the strain of T. reesei used to produce cellobiohydrolase I. In vitro pretreatment of fungal glycoproteins with Aspergillus saitoi alpha-1,2-mannosidase improved subsequent hybrid formation. It was, however, not possible to trim all fungal oligosaccharides to an acceptor substrate for mammalian glycosyltransferases. With T. reesei RUTC 30, capping glucose residues and phosphate groups were shown to be responsible for this lack of trimming. N-glycan processing in T. reesei apparently involves different steps, including alpha-1,2-mannosidase trimmings, and thus resembles the first mammalian glycosylation processes. The alpha-1,2-mannosidase trimming steps can be exploited for further in vitro and/or in vivo synthesis of complex oligosaccharides on (heterologous) glycoproteins from filamentous fungi.
 ...
PMID:In vitro conversion of the carbohydrate moiety of fungal glycoproteins to mammalian-type oligosaccharides--evidence for N-acetylglucosaminyltransferase-I-accepting glycans from Trichoderma reesei. 939 16

The molecular basis for the resistance of serogroup B Neisseria meningitidis to the bactericidal activity of normal human sera (NHS) was examined with a NHS-resistant, invasive serogroup B meningococcal isolate and genetically and structurally defined capsule-, lipooligosaccharide (LOS)-, and sialylation-altered mutants of the wild-type strain. Expression of the (alpha2-->8)-linked polysialic acid serogroup B capsule was essential for meningococcal resistance to NHS. The very NHS-sensitive phenotype of acapsular mutants (99.9 to 100% killed in 10, 25, and 50% NHS) was not rescued by complete LOS sialylation or changes in LOS structure. However, expression of the capsule was necessary but not sufficient for a fully NHS-resistant phenotype. In an encapsulated background, loss of LOS sialylation by interrupting the alpha2,3 sialyltransferase gene, lst, increased sensitivity to 50% NHS. In contrast, replacement of the lacto-N-neotetraose alpha-chain (Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc) with glucose extensions (GlcN) in a galE mutant resulted in a strain resistant to killing by 50% NHS at all time points. Encapsulated meningococci expressing a Hep2(GlcNAc)-->KDO2-->lipid A LOS without an alpha-chain demonstrated enhanced sensitivity to 50% NHS (98% killed at 30 min) mediated through the antibody-dependent classical complement pathway. Encapsulated LOS mutants expressing truncated Hep2-->KDO2-->lipid A and KDO2-->lipid A structures were also sensitive to 50% NHS (98 to 100% killed at 30 min) but, unlike the wild-type strain and mutants with larger oligosaccharide structures, they were killed by hypogammaglobulinemic sera. These data indicate that encapsulation is essential but that the LOS structure contributes to the ability of serogroup B N. meningitidis to resist the bactericidal activity of NHS.
 ...
PMID:The (alpha2-->8)-linked polysialic acid capsule and lipooligosaccharide structure both contribute to the ability of serogroup B Neisseria meningitidis to resist the bactericidal activity of normal human serum. 982 76

Gonococci (strain BS4(agar)), emerging from lag-phase during 1-1.5 h incubation in a medium containing glucose (28 mM) and either 5 microM or 50 microM sodium lactate, show enhanced capacity for their lipopolysaccharide (LPS) to be sialylated by cytidine 5'-monophospho-N-acetyl neuraminic acid. The sialyltransferase content of the lactate-treated gonococci was not greater than that of control organisms and showed no differences in LPS components. However, the total LPS content of the lactate-treated gonococci was 10-20% higher than that of control organisms, so lactate enhancement may be due to more sialyl receptors becoming available due to an overall stimulation of LPS synthesis. The protein and pentose contents of the lactate-treated gonococci were also higher than those of controls, indicating stimulation of protein synthesis and ribosome production. Electron microscopy showed hair-like external appendages on control but not on lactate-treated gonococci. The above growth conditions are unnatural. However, when concentrations of glucose and lactate were adjusted to values akin to those occurring in vivo (glucose 5 mM alone and with either 1 mM or 10 mM lactate), and gonococcal multiplication occurred during the short incubation period (1-1.5 h), lactate again induced greater contents of LPS, protein and pentose. A high content of LPS, which will contribute to pathogenicity, should be a constant feature of gonococci growing in human urogenital tissues, where lactate is ever present with glucose.
 ...
PMID:Lactate causes changes in gonococci including increased lipopolysaccharide synthesis during short-term incubation in media containing glucose. 986 75

Carbohydrate composition changes of glycoconjugates constituting the glycocalix of microvascular cells could be involved in the alterations of cell-cell interactions observed in diabetic retinopathy. In this field, we have recently reported that advanced glycation end products (AGEs) modify galactose, fucose and sialic acid contents of specific cellular glycoproteins. To better understand the mechanisms involved in glycoprotein modifications in diabetes, we now investigate whether glucose and AGEs could affect the activities of enzymes involved in galactose, fucose and sialic acid metabolism : glycosyltransferases (synthesis) and glycosidases (catabolism). For this, bovine retinal endothelial cells (BREC) and pericytes (BRP) were cultured in the presence of high glucose concentration or AGEs, and cell glycosidase and glycosyltransferase activities were measured. The same enzymatic activities were studied in the whole retina from streptozotocin-treated rats. The results show that high glucose concentration did not affect glycosidases and glycosyltransferases neither in BRP nor in BREC except for galactosyltransferase activities in BREC. Concerning BRP, only galactosyltransferase activities were altered by AGEs. In contrast, in BREC, AGEs increased beta-D galactosidase, alpha-L fucosidase and neuraminidase activities (+37%, +56%, 36% respectively) whereas galactosyltransferase, fucosyltransferase and sialyltransferase activities were decreased (-11%, -24% and -23% respectively). In the retina from diabetic rats, beta-D galactosidase, alpha-L fucosidase and neuraminidase activities increased (+70%, +57%, +78% respectively) whereas fucosyl and sialyltransferase decreased (-7% and -15% respectively). The possible consequence of these enzymatic activity changes could be a defect in the carbohydrate content of some glycoproteins that might participate in the endothelial cell dysfunctions in diabetic microangiopathy.
 ...
PMID:In vitro and in vivo alterations of enzymatic glycosylation in diabetes. 1035 22


1 2 Next >>