The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform
Anne Imberty - One of the best experts on this subject based on the ideXlab platform.
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Fold recognition study of α3-Galactosyltransferase and molecular modeling of the nucleotide sugar-binding domain
Glycobiology, 1999Co-Authors: Anne Imberty, Cédric Monier, Emmanuel Bettler, Solange Moréra, Paul S. Freemont, Manfred J. Sippl, Hannes Flöckner, Wolfgang Rüger, Christelle BretonAbstract:The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig alpha3 Galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that alpha3-Galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating alpha-helices and beta-strands. Fold recognition studies predicted that alpha3-Galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme beta-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of beta-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig alpha3-Galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of alpha3-Galactosyltransferases.
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Fold recognition study of alpha3-Galactosyltransferase and molecular modeling of the nucleotide sugar-binding domain.
Glycobiology, 1999Co-Authors: Anne Imberty, Cédric Monier, Emmanuel Bettler, Solange Moréra, Paul S. Freemont, Manfred J. Sippl, Hannes Flöckner, Wolfgang Rüger, Christelle BretonAbstract:The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig alpha3 Galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that alpha3-Galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating alpha-helices and beta-strands. Fold recognition studies predicted that alpha3-Galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme beta-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of beta-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig alpha3-Galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of alpha3-Galactosyltransferases.The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig alpha3 Galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that alpha3-Galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating alpha-helices and beta-strands. Fold recognition studies predicted that alpha3-Galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme beta-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of beta-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig alpha3-Galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of alpha3-Galactosyltransferases.
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Sequence-Function Relationships of Prokaryotic and Eukaryotic Galactosyltransferases
Journal of biochemistry, 1998Co-Authors: Christelle Breton, Emmanuel Bettler, David H. Joziasse, Roberto A. Geremia, Anne ImbertyAbstract:Galactosyltransferases are enzymes which transfer galactose from UDP-Gal to various acceptors with either retention of the anomeric configuration to form alpha1,2-, alpha1,3-, alpha1,4-, and alpha1, 6-linkages, or inversion of the anomeric configuration to form beta1, 3-, beta1,4-, and beta1-ceramide linkages. During the last few years, several (c)DNA sequences coding for Galactosyltransferases became available. We have retrieved these sequences and conducted sequence similarity studies. On the basis of both the nature of the reaction catalyzed and the protein sequence identity, these enzymes can be classified into twelve groups. Using a sensitive graphics method for protein comparison, conserved structural features were found in some of the Galactosyltransferase groups, and other classes of glycosyltransferases, resulting in the definition of five families. The lengths and locations of the conserved regions as well as the invariant residues are described for each family. In addition, the DxD motif that may be important for substrate recognition and/or catalysis is demonstrated to occur in all families but one.
Christelle Breton - One of the best experts on this subject based on the ideXlab platform.
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Fold recognition study of α3-Galactosyltransferase and molecular modeling of the nucleotide sugar-binding domain
Glycobiology, 1999Co-Authors: Anne Imberty, Cédric Monier, Emmanuel Bettler, Solange Moréra, Paul S. Freemont, Manfred J. Sippl, Hannes Flöckner, Wolfgang Rüger, Christelle BretonAbstract:The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig alpha3 Galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that alpha3-Galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating alpha-helices and beta-strands. Fold recognition studies predicted that alpha3-Galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme beta-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of beta-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig alpha3-Galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of alpha3-Galactosyltransferases.
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Fold recognition study of alpha3-Galactosyltransferase and molecular modeling of the nucleotide sugar-binding domain.
Glycobiology, 1999Co-Authors: Anne Imberty, Cédric Monier, Emmanuel Bettler, Solange Moréra, Paul S. Freemont, Manfred J. Sippl, Hannes Flöckner, Wolfgang Rüger, Christelle BretonAbstract:The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig alpha3 Galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that alpha3-Galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating alpha-helices and beta-strands. Fold recognition studies predicted that alpha3-Galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme beta-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of beta-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig alpha3-Galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of alpha3-Galactosyltransferases.The structure and fold of the enzyme responsible for the biosynthesis of the xenotransplantation antigen, namely pig alpha3 Galactosyltransferase, has been studied by means of computational methods. Secondary structure predictions indicated that alpha3-Galactosyltransferase and related protein family members, including blood group A and B transferases and Forssman synthase, are likely to consist of alternating alpha-helices and beta-strands. Fold recognition studies predicted that alpha3-Galactosyltransferase shares the same fold as the T4 phage DNA-modifying enzyme beta-glucosyltransferase. This latter enzyme displays a strong structural resemblance with the core of glycogen phosphorylase b. By using the three-dimensional structure of beta-glucosyltransferase and of several glycogen phosphorylases, the nucleotide binding domain of pig alpha3-Galactosyltransferase was built by knowledge-based methods. Both the UDP-galactose ligand and a divalent cation were included in the model during the refinement procedure. The final three-dimensional model is in agreement with our present knowledge of the biochemistry and mechanism of alpha3-Galactosyltransferases.
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Sequence-Function Relationships of Prokaryotic and Eukaryotic Galactosyltransferases
Journal of biochemistry, 1998Co-Authors: Christelle Breton, Emmanuel Bettler, David H. Joziasse, Roberto A. Geremia, Anne ImbertyAbstract:Galactosyltransferases are enzymes which transfer galactose from UDP-Gal to various acceptors with either retention of the anomeric configuration to form alpha1,2-, alpha1,3-, alpha1,4-, and alpha1, 6-linkages, or inversion of the anomeric configuration to form beta1, 3-, beta1,4-, and beta1-ceramide linkages. During the last few years, several (c)DNA sequences coding for Galactosyltransferases became available. We have retrieved these sequences and conducted sequence similarity studies. On the basis of both the nature of the reaction catalyzed and the protein sequence identity, these enzymes can be classified into twelve groups. Using a sensitive graphics method for protein comparison, conserved structural features were found in some of the Galactosyltransferase groups, and other classes of glycosyltransferases, resulting in the definition of five families. The lengths and locations of the conserved regions as well as the invariant residues are described for each family. In addition, the DxD motif that may be important for substrate recognition and/or catalysis is demonstrated to occur in all families but one.
David E. Wolf - One of the best experts on this subject based on the ideXlab platform.
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Distribution and dynamics of mouse sperm surface Galactosyltransferase: implications for mammalian fertilization.
Biochemistry, 1995Co-Authors: Richard A. Cardullo, David E. WolfAbstract:It has been proposed that a mouse sperm surface beta-1,4-Galactosyltransferase functions as a receptor for the zona pellucida during fertilization. In this paper we used two monovalent fluorescent probes specific for Galactosyltransferase: a trinitrophenylated derivative of UDP-galactose and rhodaminated alpha-lactalbumin. We found that Galactosyltransferase was initially present over the posterior head of acrosome-intact sperm but became progressively localized to the plasma membrane overlying the acrosomal region after it was cross-linked with an anti-Galactosyltransferase polyclonal antibody. Labeled mouse sperm that were treated with the calcium ionophore A23187 revealed that Galactosyltransferase remained on the posterior head after acrosomal exocytosis. However, if Galactosyltransferase was first cross-linked and redistributed with antibody and then acrosome reacted with A23187, all head fluorescence was lost. In addition, although anti-Galactosyltransferase antibody induced a surface redistribution, it did not, by itself, lead to the release of acrosin, the endpoint of the acrosome reaction. Finally, using the technique of fluorescence recovery after photobleaching, we found that, in the absence of bivalent antibody, mouse sperm surface Galactosyltransferase exhibited 40-50% recovery with a high diffusion coefficient on the anterior head (5-8 x 10(-9) cm2/s) approximately 2 times greater than on the posterior head (2-4 x 10(-9) cm2/s). When Galactosyltransferase was cross-linked and redistributed to the anterior head using the bivalent antibody, the mobile fraction decreased to 20-30% with no significant change in the diffusion coefficient.(ABSTRACT TRUNCATED AT 250 WORDS)
Henrik Clausen - One of the best experts on this subject based on the ideXlab platform.
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identification and characterization of large Galactosyltransferase gene families Galactosyltransferases for all functions
Biochimica et Biophysica Acta, 1999Co-Authors: Margarida Amado, Raquel Almeida, Tilo Schwientek, Henrik ClausenAbstract:Enzymatic glycosylation of proteins and lipids is an abundant and important biological process. A great diversity of oligosaccharide structures and types of glycoconjugates is found in nature, and these are synthesized by a large number of glycosyltransferases. Glycosyltransferases have high donor and acceptor substrate specificities and are in general limited to catalysis of one unique glycosidic linkage. Emerging evidence indicates that formation of many glycosidic linkages is covered by large homologous glycosyltransferase gene families, and that the existence of multiple enzyme isoforms provides a degree of redundancy as well as a higher level of regulation of the glycoforms synthesized. Here, we discuss recent cloning strategies enabling the identification of these large glycosyltransferase gene families and exemplify the implication this has for our understanding of regulation of glycosylation by discussing two Galactosyltransferase gene families.
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Cloning and Expression of a Proteoglycan UDP-Galactose:β-Xylose β1,4-Galactosyltransferase I A SEVENTH MEMBER OF THE HUMAN β4-Galactosyltransferase GENE FAMILY
The Journal of biological chemistry, 1999Co-Authors: Raquel Almeida, Steven B. Levery, Eric P. Bennett, Tilo Schwientek, Ulla Mandel, Hans Kresse, Henrik ClausenAbstract:Abstract A seventh member of the human β4-Galactosyltransferase family, β4Gal-T7, was identified by BLAST analysis of expressed sequence tags. The coding region of β4Gal-T7 depicts a type II transmembrane protein with sequence similarity to β4-Galactosyltransferases, but the sequence was distinct in known motifs and did not contain the cysteine residues conserved in the other six members of the β4Gal-T family. The genomic organization of β4Gal-T7 was different from previous β4Gal-Ts. Expression of β4Gal-T7 in insect cells showed that the gene product had β1,4-Galactosyltransferase activity with β-xylosides, and the linkage formed was Galβ1–4Xyl. Thus, β4Gal-T7 represents Galactosyltransferase I enzyme (xylosylprotein β1,4-Galactosyltransferase; EC 2.4.1.133), which attaches the first galactose in the proteoglycan linkage region GlcAβ1–3Galβ1–3Galβ1–4Xylβ1-O-Ser. Sequence analysis of β4Gal-T7 from a fibroblast cell line of a patient with a progeroid syndrome and signs of the Ehlers-Danlos syndrome, previously shown to exhibit reduced Galactosyltransferase I activity (Quentin, E., Gladen, A., Roden, L., and Kresse, H. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 1342–1346), revealed two inherited allelic variants, β4Gal-T7186D and β4Gal-T7206P, each with a single missense substitution in the putative catalytic domain of the enzyme. β4Gal-T7186D exhibited a 4-fold elevated K m for the donor substrate, whereas essentially no activity was demonstrated with β4Gal-T7206P. Molecular cloning of β4Gal-T7 should facilitate general studies of its pathogenic role in progeroid syndromes and connective tissue disorders with affected proteoglycan biosynthesis.
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cloning of a novel member of the udp galactose β n acetylglucosamine β1 4 Galactosyltransferase family β4gal t4 involved in glycosphingolipid biosynthesis
Journal of Biological Chemistry, 1998Co-Authors: Tilo Schwientek, Raquel Almeida, Steven B. Levery, Eric H. Holmes, Eric Bennett, Henrik ClausenAbstract:A novel putative member of the human UDP-galactose:beta-N-acetylglucosamine beta1,4-Galactosyltransferase family, designated beta4Gal-T4, was identified by BLAST analysis of expressed sequence tags. The sequence of beta4Gal-T4 encoded a type II membrane protein with significant sequence similarity to other beta1,4-Galactosyltransferases. Expression of the full coding sequence and a secreted form of beta4Gal-T4 in insect cells showed that the gene product had beta1,4-Galactosyltransferase activity. Analysis of the substrate specificity of the secreted form revealed that the enzyme catalyzed glycosylation of glycolipids with terminal beta-GlcNAc; however, in contrast to beta4Gal-T1, -T2, and -T3, this enzyme did not transfer galactose to asialo-agalacto-fetuin, asialo-agalacto-transferrin, or ovalbumin. The catalytic activity of beta4Gal-T4 with monosaccharide acceptor substrates, N-acetylglucosamine as well as glucose, was markedly activated in the presence of alpha-lactalbumin. The genomic organization of the coding region of beta4Gal-T4 was contained in six exons. All intron/exon boundaries were similarly positioned in beta4Gal-T1, -T2, and -T3. beta4Gal-T4 represents a new member of the beta4-Galactosyltransferase family. Its kinetic parameters suggest unique functions in the synthesis of neolactoseries glycosphingolipids.
Barry D. Shur - One of the best experts on this subject based on the ideXlab platform.
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Biological consequences of targeting beta 1,4-Galactosyltransferase to two different subcellular compartments
BioEssays : news and reviews in molecular cellular and developmental biology, 1995Co-Authors: Susan C. Evans, Adel Youakim, Barry D. ShurAbstract:beta 1,4-Galactosyltransferase is unusual among the glycosyltransferases in that it is found in two subcellular compartments where it performs two distinct functions. In the trans-Golgi complex, Galactosyltransferase participates in oligosaccharide biosynthesis, as do the other glycosyltransferases. On the cell surface, however, Galactosyltransferase associates with the cytoskeleton and functions as a receptor for extracellular oligosaccharide ligands. Although we now know much regarding Galactosyltransferase function in these two compartments, little is known about how it is targeted to these different sites. By cloning the Galactosyltransferase gene products, certain features of the protein have been identified that may be critical for its expression on the cell surface or retention within the Golgi complex. This article discusses recent studies which suggest that a cytoplasmic sequence unique to one Galactosyltransferase isoform is required for targeting a portion of this protein to the plasma membrane, enabling it to function as a cell adhesion molecule. These findings allow one to manipulate surface Galactosyltransferase expression, either positively or negatively, and perturb Galactosyltransferase-dependent cellular interactions during fertilization and development.
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Expressing murine beta 1,4-Galactosyltransferase in HeLa cells produces a cell surface Galactosyltransferase-dependent phenotype.
The Journal of biological chemistry, 1994Co-Authors: T. T. M. Nguyen, D. A. Hinton, Barry D. ShurAbstract:Beta 1,4-Galactosyltransferase is traditionally viewed as a biosynthetic component of the Golgi complex, but a portion of Galactosyltransferase is also expressed on the cell surface, where it has been suggested to function as a receptor for extracellular oligosaccharide ligands. Although results from a variety of studies are consistent with a cell adhesion function for Galactosyltransferase, the most rigorous test of surface Galactosyltransferase function is to produce a surface Galactosyltransferase-dependent phenotype in cells that normally express negligible levels of surface Galactosyltransferase. In agreement with previous reports, human HeLa cells were found to express low levels of Galactosyltransferase on their surface and, therefore, were stably transfected with cDNAs encoding murine Galactosyltransferase. Murine Galactosyltransferase was expressed both within the presumed Golgi complex and on the cell surface, as assayed by enzyme activity and with antiserum raised against the bacterially expressed murine enzyme. HeLa cell transfectants adhered more strongly to their extracellular substrates than did control transfectants, as evidenced by a flatter morphology in culture and a more rapid spreading upon plating. In contrast, cell spreading was low and similar among all cell types when plated on extracellular substrates that did not contain binding sites for Galactosyltransferase. Antibodies and Fab fragments against recombinant murine Galactosyltransferase inhibited the increased cell spreading characteristic of Galactosyltransferase transfectants, as did soluble recombinant Galactosyltransferase and a variety of Galactosyltransferase perturbants. Thus, expression of heterologous Galactosyltransferase produces a surface Galactosyltransferase-dependent phenotype, confirming its function as a cell adhesion molecule.
