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  • 1
    Electronic Resource
    Electronic Resource
    Identification of the Acid/Base Catalyst in Agrobacterium faecalis .beta.-Glucosidase by Kinetic Analysis of Mutants (1995)
    s.l. : American Chemical Society
    Biochemistry 34 (1995), S. 14554-14562 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00044a034
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Changing Enzymic Reaction Mechanisms by Mutagenesis: Conversion of a Retaining Glucosidase to an Inverting Enzyme (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 11594-11595 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00104a060
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    Paper (German National Licenses)
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  • 3
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    Mechanisms of the sialidase and trans-sialidase activities of bacterial sialyltransferases from glycosyltransferase family 80 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-26
    Description: Many important biological functions are mediated by complex glycan structures containing the nine-carbon sugar sialic acid (Sia) at terminal, non-reducing positions. Sia are introduced onto glycan structures by enzymes known as sialyltransferases (STs). Bacterial STs from the glycosyltransferase family GT80 are a group of well-studied enzymes used for the synthesis of sialylated glycan structures. While highly efficient at sialyl transfer, these enzymes also demonstrate sialidase and trans-sialidase activities for which there is some debate surrounding the corresponding enzymatic mechanisms. Here we propose a mechanism for STs from the glycosyltransferase family GT80 in which sialidase and trans-sialidase activities occur through reverse sialylation of CMP. The resulting CMP-Sia is then enzymatically hydrolyzed or used as a donor in subsequent ST reactions resulting in sialidase and trans-sialidase activities, respectively. We provide evidence for this mechanism by demonstrating that CMP is required for sialidase and trans-sialidase activities and that its removal with phosphatase ablates activity. We also confirm the formation of CMP-Sia using a coupled enzyme assay. A clear understanding of the sialidase and trans-sialidase mechanisms for this class of enzymes allows for more effective use of these enzymes in the synthesis of glycoconjugates.
    Print ISSN: 0959-6658
    Electronic ISSN: 1460-2423
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 4
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    Drive-through deacylation of biofilm poly-GlcNAc [Biochemistry] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-07-30
    Description: One of the survival strategies used by planktonic bacteria when under stress is to encase their community within an extracellular matrix composed of biopolymers, such as polysaccharides, DNA, and proteins, thereby forming a biofilm that adheres to surfaces and interfaces (1–3). The chemical structure of the polysaccharides involved varies widely...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 5
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    Structure-based mutagenic analysis of mechanism and substrate specificity in mammalian glycosyltransferases: Porcine ST3Gal-I (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-27
    Description: Sialyltransferases (STs) play essential roles in signaling and in the cellular recognition processes of mammalian cells by selectively installing cell-surface sialic acids in an appropriate manner both temporally and organ-specifically. The availability of the first three-dimensional structure of a mammalian (GT29) sialyltransferase has, for the first time, allowed quantitative structure/function analyses to be performed, thereby providing reliable insights into the roles of key active site amino acids. Kinetic analyses of mutants of ST3Gal-I, in conjunction with structural studies, have confirmed the mechanistic roles of His302 and His319 as general acid and base catalysts, respectively, and have quantitated other interactions with the cytosine monophosphate- N -acetyl β-neuraminic acid donor substrate. The contributions of side chains that provide key interactions with the acceptor substrate, defining its specificity, have also been quantitated. Particularly important transition-state interactions of 2.5 and 2.7 kcal mol –1 are found between the acceptor axial 4-hydroxyl and the conserved side chains of Gln108 and Tyr269, respectively. These results provide a basis for the engineering of mammalian STs to accommodate non-natural substrate analogs that should prove valuable as chemical biological probes of sialyltransferase function.
    Print ISSN: 0959-6658
    Electronic ISSN: 1460-2423
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 6
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    The structure of the Mycobacterium smegmatis trehalose synthase reveals an unusual active site configuration and acarbose-binding mode (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-27
    Description: Trehalose synthase (TreS) catalyzes the reversible conversion of maltose into trehalose in mycobacteria as one of three biosynthetic pathways to this nonreducing disaccharide. Given the importance of trehalose to survival of mycobacteria, there has been considerable interest in understanding the enzymes involved in its production; indeed the structures of the key enzymes in the other two pathways have already been determined. Herein, we present the first structure of TreS from Mycobacterium smegmatis , thereby providing insights into the catalytic machinery involved in this intriguing intramolecular reaction. This structure, which is of interest both mechanistically and as a potential pharmaceutical target, reveals a narrow and enclosed active site pocket within which intramolecular substrate rearrangements can occur. We also present the structure of a complex of TreS with acarbose, revealing a hitherto unsuspected oligosaccharide-binding site within the C-terminal domain. This may well provide an anchor point for the association of TreS with glycogen, thereby enhancing its role in glycogen biosynthesis and degradation.
    Print ISSN: 0959-6658
    Electronic ISSN: 1460-2423
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 7
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    Toward the Mechanism of Unsaturated Glucuronyl Hydrolase [Glycobiology and Extracellular Matrices] (2014)
    The American Society for Biochemistry and Molecular Biology (ASBMB)
    Details
    Publication Date: 2014-04-19
    Description: Experiments were carried out to probe the details of the hydration-initiated hydrolysis catalyzed by the Clostridium perfringens unsaturated glucuronyl hydrolase of glycoside hydrolase family 88 in the CAZy classification system. Direct 1H NMR monitoring of the enzymatic reaction detected no accumulated reaction intermediates in solution, suggesting that rearrangement of the initial hydration product occurs on-enzyme. An attempt at mechanism-based trapping of on-enzyme intermediates using a 1,1-difluoro-substrate was unsuccessful because the probe was too deactivated to be turned over by the enzyme. Kinetic isotope effects arising from deuterium-for-hydrogen substitution at carbons 1 and 4 provide evidence for separate first-irreversible and overall rate-determining steps in the hydration reaction, with two potential mechanisms proposed to explain these results. Based on the positioning of catalytic residues in the enzyme active site, the lack of efficient turnover of a 2-deoxy-2-fluoro-substrate, and several unsuccessful attempts at confirmation of a simpler mechanism involving a covalent glycosyl-enzyme intermediate, the most plausible mechanism is one involving an intermediate bearing an epoxide on carbons 1 and 2.
    Print ISSN: 0021-9258
    Electronic ISSN: 1083-351X
    Topics: Biology , Chemistry and Pharmacology
    Published by The American Society for Biochemistry and Molecular Biology (ASBMB)
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  • 8
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    GH3 {beta}-N-Acetylglucosaminidases Are Glycoside Phosphorylases [Enzymology] (2015)
    The American Society for Biochemistry and Molecular Biology (ASBMB)
    Details
    Publication Date: 2015-02-26
    Description: CAZy glycoside hydrolase family GH3 consists primarily of stereochemistry-retaining β-glucosidases but also contains a subfamily of β-N-acetylglucosaminidases. Enzymes from this subfamily were recently shown to use a histidine residue within a His-Asp dyad contained in a signature sequence as their catalytic acid/base residue. Reasons for their use of His rather than the Glu or Asp found in other glycosidases were not apparent. Through studies on a representative member, the Nag3 β-N-acetylglucosaminidase from Cellulomonas fimi, we now show that these enzymes act preferentially as glycoside phosphorylases. Their need to accommodate an anionic nucleophile within the enzyme active site explains why histidine is used as an acid/base catalyst in place of the anionic glutamate seen in other GH3 family members. Kinetic and mechanistic studies reveal that these enzymes also employ a double-displacement mechanism involving a covalent glycosyl-enzyme intermediate, which was directly detected by mass spectrometry. Phosphate has no effect on the rates of formation of the glycosyl-enzyme intermediate, but it accelerates turnover of the N-acetylglucosaminyl-enzyme intermediate ∼3-fold, while accelerating turnover of the glucosyl-enzyme intermediate several hundredfold. These represent the first reported examples of retaining β-glycoside phosphorylases, and the first instance of free β-GlcNAc-1-phosphate in a biological context.
    Print ISSN: 0021-9258
    Electronic ISSN: 1083-351X
    Topics: Biology , Chemistry and Pharmacology
    Published by The American Society for Biochemistry and Molecular Biology (ASBMB)
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  • 9
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    REPORT: Proteolytic Cleavage Driven by Glycosylation [Glycobiology and Extracellular Matrices] (2016)
    The American Society for Biochemistry and Molecular Biology (ASBMB)
    Details
    Publication Date: 2016-01-02
    Description: Proteolytic processing of human host cell factor 1 (HCF-1) to its mature form was recently shown, unexpectedly, to occur in a UDP-GlcNAc-dependent fashion within the transferase active site of O-GlcNAc-transferase (OGT) (Lazarus, M. B., Jiang, J., Kapuria, V., Bhuiyan, T., Janetzko, J., Zandberg, W. F., Vocadlo, D. J., Herr, W., and Walker, S. (2013) Science 342, 1235–1239). An interesting mechanism involving formation and then intramolecular rearrangement of a covalent glycosyl ester adduct of the HCF-1 polypeptide was proposed to account for this unprecedented proteolytic activity. However, the key intermediate remained hypothetical. Here, using a model enzyme system for which the formation of a glycosyl ester within the enzyme active site has been shown unequivocally, we show that ester formation can indeed lead to proteolysis of the adjacent peptide bond, thereby providing substantive support for the mechanism of HCF-1 processing proposed.
    Print ISSN: 0021-9258
    Electronic ISSN: 1083-351X
    Topics: Biology , Chemistry and Pharmacology
    Published by The American Society for Biochemistry and Molecular Biology (ASBMB)
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  • 10
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    Crystal structure of TarM [Microbiology] (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-02-11
    Description: Unique to Gram-positive bacteria, wall teichoic acids are anionic glycopolymers cross-stitched to a thick layer of peptidoglycan. The polyol phosphate subunits of these glycopolymers are decorated with GlcNAc sugars that are involved in phage binding, genetic exchange, host antibody response, resistance, and virulence. The search for the enzymes responsible for...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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