The Experts below are selected from a list of 708 Experts worldwide ranked by ideXlab platform
Peter Biely - One of the best experts on this subject based on the ideXlab platform.
-
Catalytic Diversity of GH30 Xylanases
'MDPI AG', 2021Co-Authors: Katarína Šuchová, Vladimír Puchart, Nikolaj Spodsberg, Kristian Mørkeberg B. R. Krogh, Peter BielyAbstract:Catalytic properties of GH30 xylanases belonging to subfamilies 7 and 8 were compared on Glucuronoxylan, modified Glucuronoxylans, arabinoxylan, rhodymenan, and xylotetraose. Most of the tested bacterial GH30-8 enzymes are specific Glucuronoxylanases (EC 3.2.1.136) requiring for action the presence of free carboxyl group of MeGlcA side residues. These enzymes were not active on arabinoxylan, rhodymenan and xylotetraose, and conversion of MeGlcA to its methyl ester or its reduction to MeGlc led to a remarkable drop in their specific activity. However, some GH30-8 members are nonspecific xylanases effectively hydrolyzing all tested substrates. In terms of catalytic activities, the GH30-7 subfamily is much more diverse. In addition to specific Glucuronoxylanases, the GH30-7 subfamily contains nonspecific endoxylanases and predominantly exo-acting enzymes. The activity of GH30-7 specific Glucuronoxylanases also depend on the presence of the MeGlcA carboxyl, but not so strictly as in bacterial enzymes. The modification of the carboxyl group of Glucuronoxylan had only weak effect on the action of predominantly exo-acting enzymes, as well as nonspecific xylanases. Rhodymenan and xylotetraose were the best substrates for exo-acting enzymes, while arabinoxylan represented hardly degradable substrate for almost all tested GH30-7 enzymes. The results expand current knowledge on the catalytic properties of this relatively novel group of xylanases
-
Non-Specific GH30_7 Endo-β-1,4-xylanase from Talaromyces leycettanus
'MDPI AG', 2021Co-Authors: Katarína Šuchová, Peter Biely, Nikolaj Spodsberg, Kristian Mørkeberg B. R. Krogh, Vladimír PuchartAbstract:This study describes the catalytic properties of a GH30_7 xylanase produced by the fungus Talaromyces leycettanus. The enzyme is an ando-β-1,4-xylanase, showing similar specific activity towards Glucuronoxylan, arabinoxylan, and rhodymenan (linear β-1,3-β-1,4-xylan). The heteroxylans are hydrolyzed to a mixture of linear as well as branched β-1,4-xylooligosaccharides that are shorter than the products generated by GH10 and GH11 xylanases. In the rhodymenan hydrolyzate, the linear β-1,4-xylooligosaccharides are accompanied with a series of mixed linkage homologues. Initial hydrolysis of Glucuronoxylan resembles the action of other GH30_7 and GH30_8 Glucuronoxylanases, resulting in a series of aldouronic acids of a general formula MeGlcA2Xyln. Due to the significant non-specific endoxylanase activity of the enzyme, these acidic products are further attacked in the unbranched regions, finally yielding MeGlcA2Xyl2-3. The accommodation of a substituted xylosyl residue in the −2 subsite also applies in arabinoxylan depolymerization. Moreover, the xylose residue may be arabinosylated at both positions 2 and 3, without negatively affecting the main chain cleavage. The catalytic properties of the enzyme, particularly the great tolerance of the side-chain substituents, make the enzyme attractive for biotechnological applications. The enzyme is also another example of extraordinarily great catalytic diversity among eukaryotic GH30_7 xylanases
-
Glucuronoxylan 3 o acetylated on uronic acid substituted xylopyranosyl residues and its hydrolysis by gh10 gh11 and gh30 endoxylanases
Carbohydrate Polymers, 2019Co-Authors: Vladimír Puchart, Kristian B R M Krogh, Peter BielyAbstract:Glucuronoxylan selectively 3-O-acetylated on uronic acid-substituted xylopyranosyl residues was prepared by deacetylation of steam explosion-extracted aspenwood acetylGlucuronoxylan by the CE6 acetylxylan esterase from Orpinomyces sp. The 3-O-acetylation of MeGlcA-substituted xylopyranosyl residues did not influence the mode of action of GH10, 11 and 30 xylanases, resulting in similar aldouronic acids as are found in alkali-extracted Glucuronoxylan hydrolysates. In all three hydrolysates of the selectively acetylated Glucuronoxylan, however, 3-O-acetylated aldouronic acids predominated over non-acetylated ones, suggesting that in native aspenwood xylan almost all MeGlcA-substituted Xylp residues are 3-O-acetylated. The results contribute to current knowledge of the mode of action of xylanases and also point to a possibility to produce novel types of xylooligosaccharides. The 3-O-acetylated aldouronic acids, along with the specifically 3-O-acetylated Glucuronoxylan, may serve as model substrates for searching for a novel type of esterase able to liberate this MeGlcA-shielded acetyl group. Such esterases are important to improve significantly saccharification yields.
-
the role of the Glucuronoxylan carboxyl groups in the action of endoxylanases of three glycoside hydrolase families a study with two substrate mutants
Biochimica et Biophysica Acta, 2015Co-Authors: Peter Biely, Anna Malovikova, Jan Hirsch, K Morkeberg B R Krogh, Anna EbringerovaAbstract:Abstract Background Bacterial appendage-dependent GH30 Glucuronoxylan hydrolases recognize the substrate through an ionic interaction of a conserved positively charged arginine with the carboxyl group of 4-O-methyl- d -glucuronic acid. One of the options to verify this interaction is preparation of enzyme mutants. An alternative approach is a chemical modification of the substrate, Glucuronoxylan, in which the free carboxyl group in all residues of MeGlcA is eliminated. Methods In this work the carboxyl groups of 4-O-methyl- d -glucuronic acid residues of an alkali extracted beechwood xylan were esterified with methanol. A water-soluble fraction of the polysaccharide methyl ester was converted by NaBH4 reduction to the second soluble derivative, 4-O-methylglucoxylan. Specific activities of several endoxylanases (EXs) of GH families 10, 11 and 30 were determined on Glucuronoxylan, and its two new uncharged derivatives. Results Elimination of the free carboxyl group from the polysaccharide did not influence activities of GH10 EXs, but resulted in 50% decrease of specific activity of GH11 EXs, and led to more than 300-fold reduction of specific activity of Erwinia chrysanthemi GH30 xylanase. Conclusions These results confirm the crucial role of the interactions between GH30 xylanases and the MeGlcA carboxyl group for efficient cleavage of the polysaccharide. Analysis of the hydrolysis products by TLC and MS confirmed that all three types of xylanases hydrolyzed uncharged Glucuronoxylans similarly as the original one. Significance The uncharged Glucuronoxylan derivatives will be useful to differentiate GH30 xylanases with various degree of selectivity for Glucuronoxylan, including fungal enzymes without the conserved arginine.
-
glucuronoyl esterases are active on the polymeric substrate methyl esterified Glucuronoxylan
FEBS Letters, 2015Co-Authors: Peter Biely, Anna Malovikova, Iveta Uhliarikova, Xin Liang Li, Dominic W S WongAbstract:Alkali extracted beechwood Glucuronoxylan methyl ester prepared by esterification of 4-O-methyl-d-glucuronic acid side residues by methanol was found to serve as substrate of microbial glucuronoyl esterases from Ruminococcus flavefaciens, Schizophyllum commune and Trichoderma reesei. The enzymatic deesterification was monitored by 1H NMR spectroscopy and evaluated on the basis of the decrease of the signal of the ester methyl group and increase of the signal of methanol. The results show for the first time the action of enzymes on polymeric substrate, which imitates more closely the natural substrate in plant cell walls than the low molecular mass artificial substrates used up to present.
Emma R Master - One of the best experts on this subject based on the ideXlab platform.
-
enzymatic production of 4 o methyl d glucaric acid from hardwood xylan
Biotechnology for Biofuels, 2020Co-Authors: Thu V Vuong, Emma R MasterAbstract:Background Dicarboxylic acids offer several applications in detergent builder and biopolymer fields. One of these acids, 4-O-methyl d-glucaric acid, could potentially be produced from Glucuronoxylans, which are a comparatively underused fraction of wood and agricultural biorefineries. Results Accordingly, an enzymatic pathway was developed that combines AxyAgu115A, a GH115 α-glucuronidase from Amphibacillus xylanus, and GOOX, an AA7 gluco-oligosaccharide oxidase from Sarocladium strictum, to produce this bio-based chemical from Glucuronoxylan. AxyAgu115A was able to release almost all 4-O-methyl d-glucuronic acid from Glucuronoxylan while a GOOX variant, GOOX-Y300A, could convert 4-O-methyl d-glucuronic acid to the corresponding glucaric acid at a yield of 62%. Both enzymes worked effectively at alkaline conditions that increase xylan solubility. Given the sensitivity of AxyAgu115A to hydrogen peroxide and optimal performance of GOOX-Y300A at substrate concentrations above 20 mM, the two-step enzyme pathway was demonstrated as a sequential, one-pot reaction. Additionally, the resulting xylan was easily recovered from the one-pot reaction, and it was enzymatically hydrolysable. Conclusions The pathway in this study requires only two enzymes while avoiding a supplementation of costly cofactors. This cell-free approach provides a new strategy to make use of the underutilized hemicellulose stream from wood and agricultural biorefineries.
-
biochemical and structural characterization of a five domain gh115 α glucuronidase from the marine bacterium saccharophagus degradans 2 40t
Journal of Biological Chemistry, 2016Co-Authors: Weijun Wang, Maija Tenkanen, Guillermo Toriz, Paul Gatenholm, Thu V Vuong, B Nocek, Xiaohui Xu, A Savchenko, Emma R MasterAbstract:Glucuronic acid (GlcAp) and/or methylglucuronic acid (MeGlcAp) decorate the major forms of xylan in hardwood and coniferous softwoods as well as many cereal grains. Accordingly, the complete utilization of Glucuronoxylans or conversion to sugar precursors requires the action of main chain xylanases as well as -glucuronidases that release the - (12)-linked (Me)GlcAp side groups. Herein, a family GH115 enzymefrom the marine bacterium Saccharophagus degradans 2-40(T), SdeAgu115A, demonstrated activity toward Glucuronoxylan and oligomers thereof with preference toward MeGlcAp linked to internal xylopyranosyl residues. Unique biochemical characteristics of NaCl activation were also observed. The crystal structure of SdeAgu115A revealed a five-domain architecture, with an additional insertion C+ domain that had significant impact on the domain arrangement of SdeAgu115A monomer and its dimerization. The participation of domain C+ in substrate binding was supported by reduced substrate inhibition upon introducing W773A, W689A, and F696A substitutions within this domain. In addition to Asp-335, the catalytic essentiality of Glu-216 was revealed by site-specific mutagenesis. A primary sequence analysis suggested that the SdeAgu115A architecture is shared by more than half of GH115 members, thus defining a distinct archetype for GH115 enzymes.
Maija Tenkanen - One of the best experts on this subject based on the ideXlab platform.
-
biochemical and structural characterization of a five domain gh115 α glucuronidase from the marine bacterium saccharophagus degradans 2 40t
Journal of Biological Chemistry, 2016Co-Authors: Weijun Wang, Maija Tenkanen, Guillermo Toriz, Paul Gatenholm, Thu V Vuong, B Nocek, Xiaohui Xu, A Savchenko, Emma R MasterAbstract:Glucuronic acid (GlcAp) and/or methylglucuronic acid (MeGlcAp) decorate the major forms of xylan in hardwood and coniferous softwoods as well as many cereal grains. Accordingly, the complete utilization of Glucuronoxylans or conversion to sugar precursors requires the action of main chain xylanases as well as -glucuronidases that release the - (12)-linked (Me)GlcAp side groups. Herein, a family GH115 enzymefrom the marine bacterium Saccharophagus degradans 2-40(T), SdeAgu115A, demonstrated activity toward Glucuronoxylan and oligomers thereof with preference toward MeGlcAp linked to internal xylopyranosyl residues. Unique biochemical characteristics of NaCl activation were also observed. The crystal structure of SdeAgu115A revealed a five-domain architecture, with an additional insertion C+ domain that had significant impact on the domain arrangement of SdeAgu115A monomer and its dimerization. The participation of domain C+ in substrate binding was supported by reduced substrate inhibition upon introducing W773A, W689A, and F696A substitutions within this domain. In addition to Asp-335, the catalytic essentiality of Glu-216 was revealed by site-specific mutagenesis. A primary sequence analysis suggested that the SdeAgu115A architecture is shared by more than half of GH115 members, thus defining a distinct archetype for GH115 enzymes.
-
glucuronic acid in arabidopsis thaliana xylans carries a novel pentose substituent
International Journal of Biological Macromolecules, 2015Co-Authors: Sunli Chong, Sanna Koutaniemi, Minna Juvonen, Marta Derbamaceluch, Ewa J Mellerowicz, Maija TenkanenAbstract:Glucuronic acids in Arabidopsis thaliana xylans exist in 4-O-methylated (MeGlcA) and non-methylated (GlcA) forms at a ratio of about 3:2. The matrix-assisted laser desorption/ionization mass spectrometry analysis of the endoxylanase liberated acidic oligosaccharides from the Arabidopsis inflorescence stem showed that two peaks with GlcA (GlcA-Xyl4Ac1 and GlcA-Xyl5Ac2) had abnormally high intensities, as well as different tandem mass spectra, than their 4-O-methylated counterparts. These peaks were interestingly enriched in the xylan biosynthesis mutant irx7 and irx9-1. Multi-stages fragmentation analysis using negative ion electrospray-ion trap mass spectrometry indicated that this GlcA was further carrying a pentose residue in the Glucuronoxylan-derived oligosaccharide from irx9-1. The structure was also identified in Arabidopsis wild type. The results prove evidence of a new pentose substitution on the GlcA residue of Arabidopsis GX, which is likely present in the primary walls.
-
thermostable recombinant xylanases from nonomuraea flexuosa and thermoascus aurantiacus show distinct properties in the hydrolysis of xylans and pretreated wheat straw
Biotechnology for Biofuels, 2011Co-Authors: Junhua Zhang, Matti Siikaaho, Maija Tenkanen, Terhi Puranen, Ming Tang, Liisa ViikariAbstract:In the hydrolysis of lignocellulosic materials, thermostable enzymes decrease the amount of enzyme needed due to higher specific activity and elongate the hydrolysis time due to improved stability. For cost-efficient use of enzymes in large-scale industrial applications, high-level expression of enzymes in recombinant hosts is usually a prerequisite. The main aim of the present study was to compare the biochemical and hydrolytic properties of two thermostable recombinant glycosyl hydrolase families 10 and 11 (GH10 and GH11, respectively) xylanases with respect to their potential application in the hydrolysis of lignocellulosic substrates. The xylanases from Nonomuraea flexuosa (Nf Xyn11A) and from Thermoascus aurantiacus (Ta Xyn10A) were purified by heat treatment and gel permeation chromatography. Ta Xyn10A exhibited higher hydrolytic efficiency than Nf Xyn11A toward birchwood Glucuronoxylan, insoluble oat spelt arabinoxylan and hydrothermally pretreated wheat straw, and it produced more reducing sugars. Oligosaccharides from xylobiose to xylopentaose as well as higher degree of polymerization (DP) xylooligosaccharides (XOSs), but not xylose, were released during the initial hydrolysis of xylans by Nf Xyn11A, indicating its potential for the production of XOS. The mode of action of Nf Xyn11A and Ta Xyn10A on Glucuronoxylan and arabinoxylan showed typical production patterns of endoxylanases belonging to GH11 and GH10, respectively. Because of its high catalytic activity and good thermostability, T. aurantiacus xylanase shows great potential for applications aimed at total hydrolysis of lignocellulosic materials for platform sugars, whereas N. flexuosa xylanase shows more significant potential for the production of XOSs.
-
an α glucuronidase of schizophyllum commune acting on polymeric xylan
Journal of Biotechnology, 2000Co-Authors: Maija Tenkanen, Matti SiikaahoAbstract:The main α-glucuronidase (EC 3.2.1.131) of the fungus Schizophyllum commune was purified to homogeneity using standard chromatographic methods; anion exchange, hydrophobic interaction chromatography and gel filtration. The enzyme had a molecular mass of 125 kDa as determined by SDS-polyacrylamide gel electrophoresis and a pI value of 3.6 according to isoelectric focusing. The N-terminal amino acid sequence of the S. commune α-glucuronidase did not show any homology with other α-glucuronidases. It exhibited maximal activity at pH values from 4.5 to 5.5 and was stable for 24 h between pH 6 and 8 at 40°C. The highest temperature at which the enzyme retained its full activity for 24 h at pH 5.8 was 40°C. The α-glucuronidase of S. commune was able to remove almost all 4-O-methylglucuronic acid groups from water-soluble polymeric softwood arabinoGlucuronoxylans. The action of the enzyme on birchwood acetyl-Glucuronoxylan was limited due to the high amount of acetyl substituents. The degree of hydrolysis of partially soluble deacetylated Glucuronoxylan did not exceed 50% of the theoretical maximum. However, together with a xylanase hydrolysing the xylan backbone the action of the α-glucuronidase of S. commune on Glucuronoxylan was clearly enhanced. It was apparent that the enzyme was able to remove the 4-O-methylglucuronic groups mainly from soluble substrates.
-
an α glucuronidase of schizophyllum commune acting on polymeric xylan
Journal of Biotechnology, 2000Co-Authors: Maija Tenkanen, Matti SiikaahoAbstract:The main α-glucuronidase (EC 3.2.1.131) of the fungus Schizophyllum commune was purified to homogeneity using standard chromatographic methods; anion exchange, hydrophobic interaction chromatography and gel filtration. The enzyme had a molecular mass of 125 kDa as determined by SDS-polyacrylamide gel electrophoresis and a pI value of 3.6 according to isoelectric focusing. The N-terminal amino acid sequence of the S. commune α-glucuronidase did not show any homology with other α-glucuronidases. It exhibited maximal activity at pH values from 4.5 to 5.5 and was stable for 24 h between pH 6 and 8 at 40°C. The highest temperature at which the enzyme retained its full activity for 24 h at pH 5.8 was 40°C. The α-glucuronidase of S. commune was able to remove almost all 4-O-methylglucuronic acid groups from water-soluble polymeric softwood arabinoGlucuronoxylans. The action of the enzyme on birchwood acetyl-Glucuronoxylan was limited due to the high amount of acetyl substituents. The degree of hydrolysis of partially soluble deacetylated Glucuronoxylan did not exceed 50% of the theoretical maximum. However, together with a xylanase hydrolysing the xylan backbone the action of the α-glucuronidase of S. commune on Glucuronoxylan was clearly enhanced. It was apparent that the enzyme was able to remove the 4-O-methylglucuronic groups mainly from soluble substrates.
Mária Vršanská - One of the best experts on this subject based on the ideXlab platform.
-
A novel family of hemicellulolytic α-glucuronidase
FEBS Letters, 2009Co-Authors: Olena Ryabova, Mária Vršanská, Satoshi KanekoAbstract:Investigation of the xylanolytic enzyme system of the xylose-fermenting yeast Pichia stipitis resulted in the discovery of an extracellular α-glucuronidase efficiently debranching hardwood Glucuronoxylan. This activity is not exhibited by more extensively investigated α-glucuronidases of glycoside hydrolase (GH) family 67, operating on substrates in which the uronic acid is linked to the non-reducing xylopyranosyl residues of main chain fragments. The N-terminus of the purified enzyme corresponded exactly to the P. stipitis gene ABN67901 coding for a protein of unknown function. BLAST search revealed the presence of similar genes in genomes of other microorganisms. These results lead to the emergence of a new family of α-glucuronidases.
-
mode of action of glycoside hydrolase family 5 Glucuronoxylan xylanohydrolase from erwinia chrysanthemi
FEBS Journal, 2007Co-Authors: Mária Vršanská, Katarina Kolenova, Vladimír PuchartAbstract:The mode of action of xylanase A from a phytopathogenic bacterium, Erwinia chrysanthemi, classified in glycoside hydrolase family 5, was investigated on xylooligosaccharides and polysaccharides using TLC, MALDI-TOF MS and enzyme treatment with exoglycosidases. The hydrolytic action of xylanase A was found to be absolutely dependent on the presence of 4-O-methyl-d-glucuronosyl (MeGlcA) side residues in both oligosaccharides and polysaccharides. Neutral linear β-1,4-xylooligosaccharides and esterified aldouronic acids were resistant towards enzymatic action. Aldouronic acids of the structure MeGlcA3Xyl3 (aldotetraouronic acid), MeGlcA3Xyl4 (aldopentaouronic acid) and MeGlcA3Xyl5 (aldohexaouronic acid) were cleaved with the enzyme to give xylose from the reducing end and products shorter by one xylopyranosyl residue: MeGlcA2Xyl2, MeGlcA2Xyl3 and MeGlcA2Xyl4. As a rule, the enzyme attacked the second glycosidic linkage following the MeGlcA branch towards the reducing end. Depending on the distribution of MeGlcA residues on the Glucuronoxylan main chain, the enzyme generated series of shorter and longer aldouronic acids of backbone polymerization degree 3–14, in which the MeGlcA is linked exclusively to the second xylopyranosyl residue from the reducing end. Upon incubation with β-xylosidase, all acidic hydrolysis products of acidic oligosaccharides and hardwood Glucuronoxylans were converted to aldotriouronic acid, MeGlcA2Xyl2. In agreement with this mode of action, xylose and unsubstituted oligosaccharides were essentially absent in the hydrolysates. The E. chrysanthemi xylanase A thus appears to be an excellent biocatalyst for the production of large acidic oligosaccharides from Glucuronoxylans as well as an invaluable tool for determination of the distribution of MeGlcA residues along the main chain of this major plant hemicellulose.
-
mode of action of endo β 1 4 xylanases of families 10 and 11 on acidic xylooligosaccharides
Journal of Biotechnology, 2006Co-Authors: Katarina Kolenova, Mária Vršanská, Peter BielyAbstract:Mode of action of endo-beta-1,4-xylanases (EXs) of glycoside hydrolase families 10 (GH-10) and 11 (GH-11) was examined on various acidic xylooligosaccharides. As expected, none of the enzymes of GH-10 cleaved aldotetraouronic acid (MeGlcA3Xyl3), which is the shortest acidic product of the action of these EXs on Glucuronoxylan. Surprisingly, aldopentaouronic acid (MeGlcA3Xyl4) was also not attacked. Only aldohexaouronic acid (MeGlcA3Xyl5) served as a substrate and was cleaved to xylobiose and aldotetraouronic acid. These results suggested that binding of xylopyranosyl residue in the -2 subsite is prerequisite for cleavage of the linkage adjacent to the xylopyranosyl unit carrying MeGlcA. EXs of family GH-11 cleaved neither aldotetraouronic acid, nor aldopentaouronic acid, which is in agreement with their action on Glucuronoxylan. Aldohexaouronic acid was cleaved to aldopentaouronic acid and xylobiose without any production of xylose, suggesting that a xylosyl transfer reaction is involved in the degradation of the substrate by EXs of GH-11.
-
biochemical and catalytic properties of an endoxylanase purified from the culture filtrate of sporotrichum thermophile
Carbohydrate Research, 2003Co-Authors: Petros Katapodis, Mária Vršanská, Marc Claeyssens, Wim Nerinckx, Peter Biely, Basil J Macris, Dimitris Kekos, Paul ChristakopoulosAbstract:An endo-beta-1,4-xylanase (1,4-beta-D-xylan xylanoxydrolase, EC 3.2.1.8) present in culture filtrates of Sporotrichum thermophile ATCC 34628 was purified to homogeneity by Q-Sepharose and Sephacryl S-200 column chromatographies. The enzyme has a molecular mass of 25,000 Da, an isoelectric point of 6.7, and is optimally active at pH 5 and at 70 degrees C. Thin-layer chromatography (TLC) analysis showed that endo-xylanase liberates mainly xylose (Xyl) and xylobiose (Xyl2) from beechwood 4-O-methyl-D-Glucuronoxylan, O-acetyl-4-O-methylGlucuronoxylan and rhodymenan (a beta-(1-->4)-beta(1-->3)-xylan). Also, the enzyme releases an acidic xylo-oligosaccharide from 4-O-methyl-D-Glucuronoxylan, and an isomeric xylotetraose and an isomeric xylopentaose from rhodymenan. Analysis of reaction mixtures by high performance liquid chromatography (HPLC) revealed that the enzyme cleaves preferentially the internal glycosidic bonds of xylooligosaccharides, [1-3H]-xylooligosaccharides and xylan. The enzyme also hydrolyses the 4-methylumbelliferyl glycosides of beta-xylobiose and beta-xylotriose at the second glycosidic bond adjacent to the aglycon. The endoxylanase is not active on pNPX and pNPC. The enzyme mediates a decrease in the viscosity of xylan associated with a release of only small amounts of reducing sugar. The enzyme is irreversibly inhibited by series of omega-epoxyalkyl glycosides of D-xylopyranose. The results suggest that the endoxylanase from S. thermophile has catalytic properties similar to the enzymes belonging to family 11.
-
inverting character of α glucuronidase a from aspergillus tubingensis
Biochimica et Biophysica Acta, 2000Co-Authors: Peter Biely, Mária Vršanská, R.p. De Vries, J VisserAbstract:Abstract α-Glucuronidase A from Aspergillus tubingensis was found to be capable of liberating 4- O -methyl- D -glucuronic acid (MeGlcA) only from those beechwood Glucuronoxylan fragments in which the acid is attached to the non-reducing terminal xylopyranosyl residue. Reduced aldotetrauronic acid, 4- O -methyl- D -glucuronosyl-α-1,2- D -xylopyranosyl-β-1,4-xylopyranosyl-β-1,4-xylitol, was found to be a suitable substrate to follow the stereochemical course of the hydrolytic reaction catalyzed by the purified enzyme. The configuration of the liberated MeGlcA was followed in a D 2 O reaction mixture by 1 H-NMR spectroscopy. It was unambiguously established that MeGlcA was released from the substrate as its β-anomer from which the α-anomer was formed on mutarotation. This result represents the first experimental evidence for the inverting character of a microbial α-glucuronidase, a member of glycosyl hydrolase family 67 (EC 3.1.1.139).
William S. York - One of the best experts on this subject based on the ideXlab platform.
-
biochemical control of xylan biosynthesis which end is up
Current Opinion in Plant Biology, 2008Co-Authors: William S. York, Malcolm A OneillAbstract:Xylans are major components of land plant secondary cell walls and are required for normal plant growth and development. Secondary walls also account for the bulk of lignocellulosic biomass, a potential feedstock for large-scale production of biofuels. Glucuronoxylan and arabinoxylan affect the conversion of lignocellulosic biomass to fermentable sugar, a crucial and expensive step in biofuel production. Thus, knowledge of xylan biosynthesis may provide tools to modify secondary cell wall structure and thereby improve the bioprocessing characteristics of biomass. Recent studies have shown that Glucuronoxylan structure and biosynthesis are far more complex than previously appreciated and the number of glycosyltransferases implicated in this process continues to increase. New hypotheses regarding the mechanisms of Glucuronoxylan biosynthesis challenge some widely held views.
-
arabidopsis irregular xylem8 and irregular xylem9 implications for the complexity of Glucuronoxylan biosynthesis
The Plant Cell, 2007Co-Authors: Maria J Pena, Alan G. Darvill, Malcolm A Oneill, Ruiqin Zhong, Gongke Zhou, Elizabeth A Richardson, William S. YorkAbstract:Mutations of Arabidopsis thaliana IRREGULAR XYLEM8 ( IRX8 ) and IRX9 were previously shown to cause a collapsed xylem phenotype and decreases in xylose and cellulose in cell walls. In this study, we characterized IRX8 and IRX9 and performed chemical and structural analyses of Glucuronoxylan (GX) from irx8 and irx9 plants. IRX8 and IRX9 are expressed specifically in cells undergoing secondary wall thickening, and their encoded proteins are targeted to the Golgi, where GX is synthesized. 1 H-NMR spectroscopy showed that the reducing end of Arabidopsis GX contains the glycosyl sequence 4-β-d-Xyl p -(1→4)-β-d-Xyl p -(1→3)-α-l-Rha p -(1→2)-α-d-Gal p A-(1→4)-d-Xyl p , which was previously identified in birch ( Betula verrucosa ) and spruce ( Picea abies ) GX. This indicates that the reducing end structure of GXs is evolutionarily conserved in woody and herbaceous plants. This sequence is more abundant in irx9 GX than in the wild type, whereas irx8 and fragile fiber8 ( fra8 ) plants are nearly devoid of it. The number of GX chains increased and the GX chain length decreased in irx9 plants. Conversely, the number of GX chains decreased and the chain length heterodispersity increased in irx8 and fra8 plants. Our results suggest that IRX9 is required for normal GX elongation and indicate roles for IRX8 and FRA8 in the synthesis of the glycosyl sequence at the GX reducing end.