144939-65-1Relevant articles and documents
Major change in regiospecificity for the exo-1,3-β-glucanase from Candida albicans following its conversion to a glycosynthase
Nakatani,Larsen,Cutfield,Cutfield
, p. 3318 - 3326 (2014)
The exo-1,3-β-glucanase (Exg) from Candida albicans is involved in cell wall β-d-glucan metabolism and morphogenesis through its hydrolase and transglycosidase activities. Previous work has shown that both these activities strongly favor β-1,3-linkages. The E292S Exg variant displayed modest glycosynthase activity using α-d-glucopyranosyl fluoride (α-GlcF) as the donor and pNP-β-d-glucopyranoside (pNPGlc) as the acceptor but surprisingly showed a marked preference for synthesizing β-1,6-linked over β-1,3- and β-1,4-linked disaccharide products. With pNPXyl as the acceptor, the preference became β-1,4 over β-1,3. The crystal structure of the glycosynthase bound to both of its substrates, α-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 β-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°flip that explains the observed variable regiospecificity. The p-nitrophenyl group on the acceptor most likely influences the unexpectedly observed β-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.
Isolation and characterization of a novel α-glucosidase with transglycosylation activity from Arthrobacter sp. DL001
Zhou, Kun,Luan, Hong-Wei,Hu, Ying,Ge, Guang-Bo,Liu, Xing-Bao,Ma, Xiao-Chi,Hou, Jie,Wang, Xiu-Li,Yang, Ling
experimental part, p. 48 - 57 (2012/09/07)
A strain of Arthrobacter sp. DL001 with high transglycosylation activity was successfully isolated from the Yellow Sea of China. To purify the extracellular enzyme responsible for transglycosylation, a four-step protocol was adopted and the enzyme with electrophoretical purity was obtained. The purified enzyme has a molecular mass of 210 kDa and displays a narrow hydrolysis specificity towards α-1,4-glucosidic bond. Its hydrolytic activity was identified as decreasing in the order of maltotriose > panose > maltose. Only 3.61% maltose activity occurs when p-nitrophenyl α-d-glycopyranoside serves as a substrate, suggesting that this enzyme belongs to the type II α-glucosidase. In addition, the enzyme was able to transfer glucosyl groups from the donors containing α-1,4-glucosidic bond specific to glucosides, xylosides and alkyl alcohols in α-1,4- or α-1,6-manners. A decreased order of activity was observed when maltose, maltotriose, panose, β-cyclodextrin and soluble starch served as glycosyl donors, respectively. When maltose was utilized as a donor and a series of p-nitrophenyl-glycosides as acceptors, the glucosidase was capable of transferring glucosyl groups to p-nitrophenyl-glucosides and p-nitrophenyl-xylosides in α-1,4- or α-1,6-manners. The yields of p-nitrophenyl-oligosaccharides could reach 42-60% in 2 h. When a series of alkyl alcohols were utilized as acceptors, the enzyme exhibited its transglycosylation activities not only to the primary alcohols but also to the secondary alcohols with carbon chain length 1-4. Therefore, all the results indicated that the purified α-glucosidase present a useful tool for the biosynthesis of oligosaccharides and alkyl glucosides.
Rare keto-aldoses from enzymatic oxidation: Substrates and oxidation products of pyranose 2-oxidase
Freimund, Stefan,Huwig, Alexander,Giffhorn, Friedrich,Koepper, Sabine
, p. 2442 - 2455 (2007/10/03)
Pyranose oxidases are known to oxidise D-glucose, D-xylose and L- sorbose to keto-aldoses, biochemically interesting compounds that may also be used for synthetic purposes in a variety of reactions. In this study pyranose oxidase from the basidiomycete Peniophora gigantea was investigated, and it was found that this enzyme is able to oxidise a broad variety of substrates very effectively. In analogy to its natural mode of action, most substrates are oxidised regioselectively in position 2. Certain compounds, however, are converted into 3-keto derivatives, and the enzyme even exhibits transfer potential, that is, disscharides are formed from β-glycosides of higher alcohols. Substrates that may be oxidised at C-2 in yields between 40-98% are D-allose, D-galactose, 6-deoxy-D-glucose, D-gentiobiose, α-D-glucopyranosyl fluoride and the very interesting 3-deoxy-D-glucose. 1,5-Anhydro-D-glucitol (1-deoxy-D-glucose) is very effectively oxidised in position 2 in 98% yield and additionally gives a product of dioxidation at C-2 and C-3 upon prolonged reaction time Selective oxidation at C-3 was found for 2-deoxy-D-glucose in very good yields and for methyl β-D-gluco- and methyl β-galactopyranoside in lower yields. All oxidation products were unequivocally characterised by NMR spectroscopy and/or chemical derivatisation. In addition, the kinetic data of the enzymatic reactions were determined for all substrates. On the basis of these data and the structural characteristics of the substrates, a model for the minimal structural requirements of the enzyme-substrate interaction is suggested. The enzyme presumably uses two different binding modes for the regioselective C-2 and the C-3 oxidations, which are described.
