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  • Articles: DFG German National Licenses  (22)
  • Electronic Resource  (22)
  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4986
    Keywords: isolation of N-glycans ; reducing oligosaccharides ; glycosyltransferase substrates ; proton NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sixteen asparagine-linked oligosaccharides ranging in size from (Man)2(GlcNAc)2 (Fuc)1 to (GlcNAc)6(Man)3(GlcNAc)2 were obtained from human α1-acid glycoprotein and fibrinogen, hen ovomucoid and ovalbumin, and bovine fetuin, fibrin and thyroglobulin by hydrazinolysis, mild acid hydrolysis and glycosidase treatment. The oligosaccharides hadN-acetylglucosamine at the reducing termini and mannose andN-acetylglucosamine residues at the non-reducing termini and were prepared for use asN-acetylglucosaminyltransferase substrates. Purification of the oligosaccharides involved gel filtration and high performance liquid chromatography on reverse phase and amine-bonded silica columns. Structures were determined by 360 MHz and 500 MHz proton nuclear magnetic resonance spectroscopy, fast atom bombardment-mass spectrometry and methylation analysis. Several of these oligosaccharides have not previously been well characterized.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Glycoconjugate journal 13 (1996), S. 693-707 
    ISSN: 1573-4986
    Keywords: mucin glycoproteins ; mucin genes ; carbohydrate antigens ; cancer ; metastasis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Mucins are high molecular weight glycoproteins that are heavily glycosylated with many oligosaccharide side chains linked O-glycosidically to the protein backbone. With the recent application of molecular biological methods, the structures of apomucins and regulation of mucin genes are beginning to be understood. At least nine human mucin genes have been identified to date. Although a complete protein sequence is known for only three human mucins (MUC1, MUC2, and MUC7), common motifs have been identified in many mucins. The pattern of tissue and cell-specific expression of these mucin genes are emerging, suggesting a distinct role for each member of this diverse mucin gene family. In epithelial cancers, many of the phenotypic markers for pre-malignant and malignant cells have been found on the carbohydrate and peptide moieties of mucin glycoproteins. The expression of carbohydrate antigens appears to be due to modification of peripheral carbohydrate structures and the exposure of inner core region carbohydrates. The expression of some of the sialylated carbohydrate antigens appears to correlate with poor prognosis and increased metastatic potential in some cancers. The exposure of peptide backbone structures of mucin glycoproteins in malignancies appears to be due to abnormal glycosylation during biosynthesis. Dysregulation of tissue and cell-specific expression of mucin genes also occurs in epithelial cancers. At present, the role of mucin glycoproteins in various stages of epithelial cell carcinogenesis (including the preneoplastic state and metastasis), in cancer diagnosis and immunotherapy is under investigation.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-4986
    Keywords: glycosyltransferase ; O-glycan ; β6-N-acetylglucosaminyltransferase ; α3-sialyltransferase ; specificity ; leukemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract To elucidate control mechanisms ofO-glycan biosynthesis in leukemia and to develop biosynthetic inhibitors we have characterized core 2 UDP-GlcNAc:Galβ1-3GalNAc-R(GlcNAc to GalNAc) β6-N-acetylglucosaminyl-transferase (EC 2.4.1.102; core 2 β6-GlcNAc-T) and CMP-sialic acid: Galβ1-3GalNAc-R α3-sialyltransferase (EC 2.4.99.4; α3-SA-T), two enzymes that are significantly increased in patients with chronic myelogenous leukemia (CML) and acute myeloid leukemia (AML). We observed distinct tissue-specific kinetic differences for the core 2 β6-GlcNAc-T activity; core 2 β6-GlcNAc-T from mucin secreting tissue (named core 2 β6-GlcNAc-T M) is accompanied by activities that synthesize core 4 [GlcNAcβ1-6(GlcNAcβ1-3)GalNAc-R] and blood group I [GlcNAcβ1-6(GlcNAcβ1-3)Galβ-R] branches; core 2 β6-GlcNAc-T in leukemic cells (named core 2 β-GlcNAc-T L) is not accompanied by these two activities and has a more restricted specificity. Core 2 β6-GlcNAc-T M and L both have an absolute requirement for the 4- and 6-hydroxyls ofN-acetylgalactosamine and the 6-hydroxyl of galactose of the Galβ1-3GalNAcα-benzyl substrate but the recognition of other substituents of the sugar rings varies, depending on the tissue. α3-sialytransferase from human placenta and from AML cells also showed distinct specificity differences, although the enzymes from both tissues have an absolute requirement for the 3-hydroxyl of the galactose residue of Galβ1-3GalNAcα-Bn. Galβ1-3(6-deoxy)GalNAcα-Bn and 3-deoxy-Galβ1-3GalNAcα-Bn competitively inhibited core 2 β6-GlcNAc-T and α3-sialyltransferase activities, respectively.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-4986
    Keywords: Synthetic oligosaccharides ; inhibitors ; N-glycans ; N-acetylglucosaminyltransferase ; biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract UDP-GlcNAc:Manα1-3R β1-2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) catalyses the conversion of [Manα1-6(Manα1-3)Manα1-6][Manα1-3]Manβ-O-R to [Manα1-6(Manα1-3)Manα1-6] [GlcNAcβ1-2Manα1-3]Manβ-O-R (R=1-4GlcNAcβ1-4GlcNAc-Asn-X) and thereby controls the conversion of oligomannose to complex and hybrid asparagine-linked glycans (N-glycans). GlcNAc-T I also catalyses the conversion of Manα1-6(Manα1-3)Manβ-O-octyl to Manα1-6(GlcNAcβ1-2Manα1-3)Manβ-O-octyl. We have therefore tested a series of synthetic analogues of Man″α1-6(Man′α1-3)Manβ-O-octyl as substrates and inhibitors for rat liver GlcNAc-T I. The 2″-deoxy and the 3″-, 4″- and 6″-O-methyl derivatives are all good substrates confirming previous observations that the hydroxyl groups of the Man″α1-6 residue do not play major roles in the binding of substrate to enzyme. In contrast, all four hydroxyl groups on the Man′α1-3 residue are essential since the corresponding deoxy derivatives either do not bind (2′- and 3′-deoxy) or bind very poorly (4′- and 6′-deoxy) to the enzyme. The 2′- and 3′-O-methyl derivatives also do not bind to the enzyme. However, the 4′-O-methyl derivative is a substrate (K m =2.6mm) and the 6′-O-methyl compound is a competitive inhibitor (K i=0.76mm). We have therefore synthesized various 4′- and 6′-O-alkyl derivatives, some with reactive groups attached to anO-pentyl spacer, and tested these compounds as reversible and irreversible inhibitors of GlcNAc-T I. The 6′-O-(5-iodoacetamido-pentyl) compound is a specific time dependent inhibitor of the enzyme. Four other 6′-O-alkyl compounds showed competitive inhibition while the remaining compounds showed little or no binding indicating that the electronic properties of the attachedO-pentyl groups influence binding.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-4986
    Keywords: GlcNAc-transferase I ; substrate specificity ; glycoprotein biosynthesis ; N-linked glycans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract UDP-GlcNAc: Manα3R β2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is the key enzyme in the synthesis of complex and hybrid N-glycans. Rat liver GlcNAc-T I has been purified more than 25,000-fold (M r 42,000). TheV max for the pure enzyme with [Manα6(Manα3)Manα6](Manα3)Manβ4GlcNAcβ4GlcNAcβ-Asn as substrate was 4.6 µmol min−1 mg−1. Structural analysis of the enzyme product by proton nuclear magnetic resonance spectroscopy proved that the enzyme adds anN-acetylglucosamine (GlcNAc) residue in β1–2 linkage to the Manα3Manβ-terminus of the substrate. Several derivatives of Manα6(Manα3)Manβ-R, a substrate for the enzyme, were synthesized and tested as substrates and inhibitors. An unsubstituted equatorial 4-hydroxyl and an axial 2-hydroxyl on the β-linked mannose of Manα6(Manα3)Manβ-R are essential for GlcNAc-T I activity. Elimination of the 4-hydroxyl of the α3-linked mannose (Man) of the substrate increases theK M 20-fold. Modifications on the α6-linked mannose or on the core structure affect mainly theK M and to a lesser degree theV max, e.g., substitutions of the Manα6 residue at the 2-position by GlcNAc or at the 3- and 6-positions by mannose lower theK M, whereas various other substitutions at the 3-position increase theK M slightly. Manα6(Manα3)4-O-methyl-Manβ4GlcNAc was found to be a weak inhibitor of GlcNAc-T I.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-4986
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-4986
    Keywords: Synthetic oligosaccharides ; inhibitors ; N-glycans ; N-acetylglucosaminyltransferase ; biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract UDP-GlcNAc: Manα1-6R β(1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man‴α1-6(GlcNAc″β1-2Man′α1-3)Manβ-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in β1-2 linkage to the 2‴-OH of the Man‴α1-6 residue. The 2‴-deoxy analogue is a competitive inhibitor (K i=0.13mm). The 2‴-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3‴-, 4‴- and 6‴-OH groups are not essential for binding or catalysis since the 3‴-, 4‴- and 6‴-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3‴-position to pentyl and substituted pentyl groups causes competitive inhibition (K i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3‴-O-(4,4-azo)pentyl group and a 3‴-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man‴α1-6 residue are essential for binding although the 2‴- and 3‴-OH face the catalytic site of the enzyme. The 4-OH group of the Manβ-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Manβ- substrate analogue. The data are compatible with our previous observations that a ‘bisecting’N-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3′-OH of the Man′α1-3 is an essential group for GlcNAc-T II since the 3′-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAcβ1-2Manα1-3Manβ-O-octyl is a good inhibitor (K i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAcβ1-2Manβ1-3Manβ- arm of the branched substrate to the enzyme is essential for catalysis.
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  • 10
    ISSN: 1573-4986
    Keywords: polypeptide GalNAc-transferase ; substrate specificity ; glycopeptides ; O-glycosylation ; mucin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The factors determining glycosylation of mucin type glycoproteins are not well understood. In the present work, we investigated the role of the peptide moiety and of the presence of O-glycan chains on O-glycosylation by UDP-GalNAc: polypeptide α-N-acetylgalactosaminyl-transferase (ppGalNAc-T). We used purified ppGalNAc-T from bovine colostrum and a series of synthetic glycopeptide and peptide substrates most of which contained sequences derived from the tandem repeat region of MUC2 mucin. The rate of incorporation of GalNAc into Thr was significantly greater than toward Ser residues. The presence of one or two GalNAc-Thr moieties in the substrate significantly reduced enzyme activity, and this effect was more pronounced when the disaccharide Galβ1–3GalNAc was present. Thus the sequential attachment of a second GalNAc residue in the vicinity of a pre-existing GalNAc-Thr or Galβ1–3GalNAc-Thr occurs at a slower rate than primary glycosylation of carbohydrate-free peptide. Analysis of products by HPLC showed that the enzyme was selective in glycosylating peptides or glycopeptides with the PTTTPIST sequence in that the preferred primary glycosylation site was the third Thr from the aminoterminal end; secondary glycosylation depended on the site of the primary glycosylation. Negatively but not positively charged amino acids on the carboxy-terminal side of the putative secondary glycosylation site resulted in high activity suggesting charge-charge interactions of substrates with the enzyme. These studies indicate that O-glycosylation by bovine colostrum ppGalNAc-T is a selective process dependent on both the amino acid sequence and prior glycosylation of peptide substrates.
    Type of Medium: Electronic Resource
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