Synthesis of Complex Oligosaccharides by Using a Mutated (1,3)--D-Glucan Endohydrolase from Barley
作者:Jon K. Fairweather、Maria Hrmova、Simon J. Rutten、Geoffrey B. Fincher、Hugues Driguez
DOI:10.1002/chem.200304733
日期:2003.6.6
Complexoligosaccharides with newly formed (1,3)-beta-glycosidic linkages were obtained in good to excellent yields when substituted or unsubstituted alpha-laminaribiosyl fluorides, acting as donors, were condensed onto mono- and disaccharide beta-D-hexopyranoside acceptors by using a (1,3)-beta-D-glycosynthase. These linear and branched (1,3)-beta-linked oligosaccharides could prove to be important
p-Nitrophenyl and eugenyl β-primeveroside (6-O-β-D-xylopyranosyl-β-D-glucopyranoside) hydrolytic activity was found in culture filtrate from Penicillium multicolor IAM7153, and the enzyme was isolated. The enzyme was purified as a β-primeverosidase-like enzyme by precipitation with ammonium sulfate followed by successive chromatographies on Phenyl Sepharose, Mono Q, and β-galactosylamidine affinity columns. The molecular mass was estimated to be 50 kDa by SDS–PAGE and gel filtration. The purified enzyme was highly specific toward the substrate p-nitrophenyl β-primeveroside, which was cleaved in an endo-manner into primeverose and p-nitrophenol, but a series of β-primeveroside as aroma precursors were hydrolyzed only slightly as substrates for the enzyme. In analyses of its hydrolytic action and kinetics, the enzyme showed narrow substrate specificity with respect to the aglycon and glycon moieties of the diglycoside. We conclude that the present enzyme is a kind of β-diglycosidase rather than β-primeverosidase.
6-glucanase capable of hydrolysing β-1,6-glucans: yeast β-glucan from Saccharomyces cerevisiae and pustulan from Lasallia pustulata. The main hydrolysis product is the valuable disaccharide gentiobiose. Gentiobiose is used as a flavour enhancer due to its refreshing bitter taste, similar to chocolate and coffee.
Major Change in Regiospecificity for the Exo-1,3-β-glucanase from <i>Candida albicans</i> following Its Conversion to a Glycosynthase
作者:Y. Nakatani、D. S. Larsen、S. M. Cutfield、J. F. Cutfield
DOI:10.1021/bi500239m
日期:2014.5.27
The exo-1,3-beta-glucanase (Exg) from Candida albicans is involved in cell wall beta-D-glucan metabolism and morphogenesis through its hydrolase and transglycosidase activities. Previous work has shown that both these activities strongly favor beta-1,3-linkages. The E292S Exg variant displayed modest glycosynthase activity using alpha-D-glucopyranosyl fluoride (alpha-GlcF) as the donor and pNP-beta-D-glucopyranoside (pNPGlc) as the acceptor but surprisingly showed a marked preference for synthesizing beta-1,6-linked over beta-1,3- and beta-1,4-linked disaccharide products. With pNPXyl as the acceptor, the preference became beta-1,4 over beta-1,3. The crystal structure of the glycosynthase bound to both of its substrates, alpha-GlcF and pNPGlc, is the first such ternary complex structure to be determined. The results revealed that the donor bound in the -1 subsite, as expected, while the acceptor was oriented in the +1 subsite to facilitate beta-1,6-linkage, thereby supporting the results from solution studies. A second crystal structure containing the major product of glycosynthesis, pNP-gentiobiose, showed that the -1 subsite allows another docking position for the terminal sugar; i.e., one position is set up for catalysis, whereas the other is an intermediate stage prior to the displacement of water from the active site by the incoming sugar hydroxyls. The +1 subsite, an aromatic "clamp", permits several different sugar positions and orientations, including a 180 degrees flip that explains the observed variable regiospecificity. The p-nitrophenyl group on the acceptor most likely influences the unexpectedly observed beta-1,6-specificity through its interaction with F229. These results demonstrate that tailoring the specificity of a particular glycosynthase depends not only on the chemical structure of the acceptor but also on understanding the structural basis of the promiscuity of the native enzyme.
β-Mannosynthase: Synthesis ofβ-Mannosides with a Mutantβ-Mannosidase
作者:Oyekanmi Nashiru、David L. Zechel、Dominik Stoll、Taraneh Mohammadzadeh、R. Antony J. Warren、Stephen G. Withers
Engineering enzymes: The glutamic acid nucleophile of a retaining β-mannosidase has been replaced with a serine residue to form a β-mannosynthase. When the new enzyme is provided with an α-mannosyl fluoride donor and an appropriate acceptor, β-mannoside linkages are synthesized. Remarkably, α-mannosyl fluoride can be generated in situ by providing the mannosynthase with excess fluoride ion.