Purification and characterization of thermoalkalophilic xylanase isolated from the Enterobacter sp. MTCC 5112

Thermoalkalophilic Enterobacter sp. MTCC 5112 was isolated from a sediment sample collected from the Mandovi estuary on the west coast of India. This culture produced extracellular xylanase. The xylanase enzyme was isolated by ammonium sulfate (80%) fractionation and purified to homogeneity using size exclusion and ion exchange chromatography. The molecular mass of the xylanase was approximately 43 kDa. The optimal pH of the xylanase activity was 9, and at room temperature it showed 100% stability at pH 7, 8 and 9 for 3 h. The optimal temperature for the enzyme activity was 100 degrees C at pH 9.0. At 80 degrees C and pH 9, 90% of the enzyme activity was retained after 40 min. At 70 and 60 degrees C, the enzyme retained 64% and 85% of its activity after 18 h, respectively, while at 50 degrees C and pH 9 the enzyme remained stable for days. For xylan, the enzyme gave a K(m) value of 3.3 mg ml(-1) and a V(max) value of 5,000 micromol min(-1) mg(-1) when the reaction was carried out at 100 degrees C and pH 9. In the presence of metal ions such as Co(2+), Zn(2+), Fe(2+), Cu(2+), Mg(2+) and Ca(2+) the activity of the enzyme increased, whereas strong inhibition of enzyme activity was observed in the presence of Hg(2+) and EDTA. To the best of our knowledge, this is the first report on the production of xylanase by this bacterium.

Cloning and characterization of a cold-active xylanase enzyme from an environmental DNA library

There is a great interest in xylanases due to the wide variety of industrial applications for these enzymes. We cloned a xylanase gene (xyn8) from an environmental genomic DNA library. The encoded enzyme was predicted to be 399 amino acids with a molecular weight of 45.9 kD. The enzyme was categorized as a glycosyl hydrolase family 8 member based on sequence analysis of the putative catalytic domain. The purified enzyme was thermolabile, had an activity temperature optimum of 20 degrees C on native xylan substrate, and retained significant activity at lower temperatures. At 4 degrees C, the apparent K (m) was 3.7 mg/ml, and the apparent k (cat) was 123/s.

Rapid and selective isolation of β-xylosidase through an activity-based chemical approach

beta-Xylosidase is a key enzyme in the xylanolytic system with a great potential in many biotechnological applications, especially in the food as well as the pulp and paper industries. We have developed a chemical approach for the rapid screening and isolation of beta-xylosidase. Activity probe LCL-6X targeting beta-xylosidase was utilized in this study. It carries a beta-xylopyranosyl recognition head, a latent trapping device consisting of a 2-fluoromethylphenoxyl group, and a biotin reporter group. The biotin reporter group serves both as a readout device and as a tool for enriching the labeled proteins. LCL-6X could selectively label a model beta-xylosidase from Trichoderma koningii. All other bystander proteins used in this study, including phosphorylase b, BSA, ovalbumin, carbonic anhydrase, and trypsin inhibitor, gave negligible cross-labeling effect. With the assistance of streptavidin agarose beads and mass spectrophotometry for the recovery and identification of the biotinylated proteins, we demonstrated that LCL-6X could be successfully applied to identify a bi-functional enzyme with alpha-L-arabinofuranosidase/beta-xylosidase activity from the total protein extract of a Pichia expressing system and a prospective beta-xylosidase in the culture medium of Aspergillus fumigatus. The beta-xylosidase activities from numerous microbes were also screened using the LCL-6X probe. Preliminary results showed significant differences among these microbial sources and some distinct protein bands were observed. Thus, we have successfully developed a novel chemical probe that has potential applications in xylan-related research.

Evolution of a carbohydrate binding module into a protein-specific binder

A carbohydrate binding module, CBM4-2, derived from the xylanase (Xyn 10A) of Rhodothermus marinus has been used as a scaffold for molecular diversification. Its binding specificity has been evolved to recognise a quite different target, a human monoclonal IgG4. In order to understand the basis for this drastic change in specificity we have further investigated the target recognition of the IgG4-specific CBMs. Firstly, we defined that the structure target recognised by the selected CBM-variants was the protein and not the carbohydrates attached to the glycoprotein. We also identified key residues involved in the new specificity and/or responsible for the swap in specificity, from xylan to human IgG4. Specific changes present in all these CBMs included mutations not introduced in the design of the library from which the specific clones were selected. Reversion of such mutations led to a complete loss of binding to the target molecule, suggesting that they are critical for the recognition of human IgG4. Together with the mutations introduced at will, they had transformed the CBM scaffold into a protein binder. We have thus shown that the scaffold of CBM4-2 is able to harbour molecular recognition for either carbohydrate or protein structures.

Purification, functional characterization, cloning, and identification of mutants of a seed-specific arabinan hydrolase in Arabidopsis

This work describes the purification and characterization of an enzyme that exhibits arabinan hydrolase activity in seeds of Arabidopsis thaliana. The enzyme, designated XYL3, had an apparent molecular mass of 80 kDa when purified to homogeneity, and was identified using MALDI-TOF (matrix-assisted laser desorption ionization-time of flight) as a putative beta-D-xylosidase that belongs to family 3 of glycoside hydrolases encoded by gene At5g09730. XYL3 hydrolysed synthetic substrates such as p-nitrophenyl-alpha-L-arabinofuranoside and p-nitrophenyl-beta-D-xyloside with similar catalytic efficiency. XYL3 released L-arabinose from (1-->5)-alpha-L-arabinofuranobiose, arabinoxylan, sugar beet arabinan, and debranched arabinan. The enzyme hydrolysed both arabinosyl-substituted side group residues and terminal arabinofuranosyl residues (1-->5)-alpha-linked to the arabinan backbone. This indicates that XYL3 is able to degrade all terminal arabinosyl residues and suggests that it participates in the in-vivo hydrolysis of arabinan. Analysis of gene expression patterns by semi-quantitative RT-PCR, in-situ hybridization and a promoter-GUS fusion demonstrated that AtBX3 was specifically expressed in the seed endosperm at the globular stage of the embryo. Immunolocalization using LM6 anti-arabinan antisera found that arabinan, the XYL3 substrate, was also present in this seed tissue. T-DNA null mutants for AtBX3 were identified. The mutant plants lacked the alpha-L-arabinofuranosidase and beta-D-xylosidase activities corresponding to XYL3. Mutants showed reduced seed size and are delayed in seedling germination compared with the wild type.

Purification and properties of a xylanase from Ceriporiopsis subvermispora cultivated on Pinus taeda

The production of hemicellulose and cellulose degrading enzymes by the white-rot fungus Ceriporiopsis subvermispora was determined while growing in Pinus taeda wood chips. Enzymes produced by the fungus were extracted after 30 days of cultivation and at least two different xylanases were secreted. An endo-(1,4)-beta-xylanase was purified by means of ultrafiltration, anion exchange chromatography and gel filtration. Its molecular mass was 29 kDa and the pH and temperature optima were 5.0 and 60 degrees C, respectively. The endo-xylanase was able to hydrolyze xylan to principally xylotriose and xylotetraose and it has different activities against different xylans. With birchwood xylan as substrate, the enzyme showed a K(m) of 1.93 mg/ml and specific activity of 538 units/mg protein at 50 degrees C.

Inexpensive one-step purification of polypeptides expressed in Escherichia coli as fusions with the family 9 carbohydrate-binding module of xylanase 10A from T. maritima

A novel inexpensive affinity purification technology is described based on recombinant expression in Escherichia coli of the polypeptide or protein target fused through its N-terminus to TmXyn10ACBM9-2 (CBM9), the C-terminal family 9 carbohydrate-binding module of xylanase 10A from Thermotoga maritima. Measured association constants (K(a)) for adsorption of CBM9 to insoluble allomorphs of cellulose are between 2 x 10(5) and 8 x 10(6) M(-1). CBM9 also binds a range of soluble sugars, including glucose. As a result, a 1M glucose solution is effective in eluting CBM9 and CBM9-tagged fusion proteins from a very inexpensive commercially-available cellulose-based capture column. A processing site is encoded at the C-terminus of the tag to facilitate its rapid and quantitative removal by Factor X(a) to recover the desired target protein sequence following affinity purification. Fusion of the CBM9 affinity tag to the N-terminus of green fluorescent protein (GFP) from the jellyfish, Aquorin victoria, is shown to yield >200 mgl(-1) of expressed soluble fusion protein that can be affinity separated from clarified cell lysate to a purity of >95% at a yield of 86%.

Simultaneous refolding/purification of xylanase with a microwave treated smart polymer

Affinity precipitation with a smart polymer, Eudragit S-100 (a methyl methacrylate polymer), was exploited for simultaneous refolding and purification of xylanase. Affinity precipitation consisted of this reversibly soluble-insoluble polymer-binding xylanase selectively. The complex was precipitated by lowering the pH and xylanase was eluted off the polymer using 1 M NaCl. For refolding experiments, the commercial preparation of Aspergillus niger xylanase was denatured with 8 M urea. Addition of microwave irradiated Eudragit S-100 and affinity precipitation led to recovery of 96% enzyme activity by refolding. Simultaneously, the enzyme was purified 45 times. Thermally inactivated preparation, when subjected to similar steps, led to 95% recovery of enzyme activity with 42-fold purification. The strategy has the potential for recovering pure proteins in active forms from overexpressed proteins, which generally form inclusion bodies in E. coli.

Crystallization and preliminary X-ray analysis of reducing-end xylose-releasing exo-oligoxylanase from Bacillus halodurans C-125

The reducing-end xylose-releasing exo-oligoxylanase (Rex) from Bacillus halodurans C-125, a novel family GH8 glycoside hydrolase, was crystallized by the hanging-drop vapour-diffusion method using 13.6 mg ml(-1) purified Rex, 5.6%(v/v) polyethylene glycol 4000, 70 mM sodium acetate pH 4.6 and 30%(v/v) glycerol. Suitable crystals grew after incubation for 5 d at 293 K. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 52.69, b = 86.02, c = 87.92 A. X-ray diffraction data were collected at a resolution of 1.35 A.

Crystallization and preliminary X-ray analysis of alpha-xylosidase from Escherichia coli

Glycoside hydrolases have been implicated in many biological processes. To date, they have been classified into 93 glycoside hydrolase (GH) families based on amino-acid sequence similarity. alpha-Xylosidase from Escherichia coli belongs to GH family 31 and catalyzes the release of alpha-xylose from the non-reducing terminal side of alpha-xyloside. Single crystals of alpha-xylosidase have been grown by vapour diffusion at 293 K from 10%(w/v) PEG 20K, 2%(v/v) 2-propanol, 2%(v/v) glycerol and 0.1 M 2-morpholinoethanesulfonic acid pH 5.5. These crystals belong to space group P2(1)2(1)2(1) and X-ray diffraction data were collected to a resolution of 2.75 A. Crystals of selenomethionyl-substituted alpha-xylosidase were also obtained, which diffracted to at least 3.0 A. Based on the value of VM, the asymmetric unit in these crystals was assumed to contain six molecules.

Sequencing and expression of the gene encoding the Clostridium stercorarium beta-xylosidase Xyl43B in Escherichia coli

The Clostridium stercorarium F-9 xyl43B gene encoding the beta-xylosidase Xyl43B consists of an open reading frame of 1,491 nucleotides that encodes a putative protein, classified in family 43, of 497 amino acids with a predicted molecular weight of 56,355. The deduced amino acid sequence of Xyl43B has sequence similarity with beta-xylosidases from Bacteriodes thetaiotaomicron (57% sequence identity), Prevotella ruminicola (45%), Streptomyces coelicolor (40%), and Clostridium acetobutylicum (36%), all of which have been classified in family 43 of the glycoside hydrolases. Xyl43B was purified from a recombinant Escherichia coli and characterized. The optimum pH of the purified enzyme was 3.5 and it was stable over pH from 3.0 to 8.0. Its optimum temperature was 80 degrees C and it showed thermostability in the temperature range from 50 to 70 degrees C. Xyl43B had a K(m) of 6.2 mM and a V(max) of 15 micromol min(-1) mg(-1) for p-nitrophenyl-beta-D-xylopyranoside.

Single mutations of residues outside the active center of the xylanase Xys1Δ fromStreptomyces halstediiJM8 affect its activity

Mutagenesis of the xylanase Xys1 of Streptomyces halstedii JM8 has been done by error prone PCR. Mutants with modified hydrolytic activity were isolated, the recombinant variant proteins purified and the catalytic activities of each one determined and compared with the wild type enzyme. Two of the isolated single point mutants, m1 (G133D) and m8 (N148D), showed 22-25% increase in specific activity towards xylan compared to wild type xylanase. Two other mutants, m5a (D175A) and m7 (T160A), showed a significant reduction in specific activity of 40-50% with respect to the wild type enzyme. These residues are mainly located in the beta alpha-loops of the xylanase, the region showing the main structural divergences within family 10 of xylanases. This study shows the usefulness of random mutagenesis to point out some key residues not directly involved in the active center, but in which mutation produces subtle structural rearrangements affecting the enzymatic function.

Overexpression and characterization of two unknown proteins, YicI and YihQ, originated from Escherichia coli

The proteins encoded in the yicI and yihQ gene of Escherichia coli have similarities in the amino acid sequences to glycoside hydrolase family 31 enzymes, but they have not been detected as the active enzymes. The functions of the two proteins have been first clarified in this study. Recombinant YicI and YihQ produced in E. coli were purified and characterized. YicI has the activity of alpha-xylosidase. YicI existing as a hexamer shows optimal pH at 7.0 and is stable in the pH range of 4.7-10.1 with incubation for 24h at 4 degrees C and also is stable up to 47 degrees C with incubation for 15 min. The enzyme shows higher activity against alpha-xylosyl fluoride, isoprimeverose (6-O-alpha-xylopyranosyl-glucopyranose), and alpha-xyloside in xyloglucan oligosaccharides. The alpha-xylosidase catalyzes the transfer of alpha-xylosyl residue from alpha-xyloside to xylose, glucose, mannose, fructose, maltose, isomaltose, nigerose, kojibiose, sucrose, and trehalose. YihQ exhibits the hydrolysis activity against alpha-glucosyl fluoride, and so is an alpha-glucosidase, although the natural substrates, such as alpha-glucobioses, are scarcely hydrolyzed. alpha-Glucosidase has been found for the first time in E. coli.

Purification and characterization of thermostable xylanase and beta-xylosidase by the thermophilic bacterium Bacillus thermantarcticus

Bacillus thermantarcticus, a thermophilic bacterium isolated from Antarctic geothermal soil near the crater of Mount Melbourne, produced extracellular xylanase (1,4-beta-D-xylan xylanohydrolase; E.C. 3.2.1.8) and beta-xylosidase (1,4-beta-D-xylan xylohydrolase; E.C. 3.2.1.37). Each extracellular enzyme was separated by gel filtration with Sephacryl S-200 and further purified to homogeneity (119-fold for xylanase and 160-fold for beta-xylosidase). The optimum temperatures were 80 degrees C for xylanase at pH 5.6 and 70 degrees C for beta-xylosidase at pH 6.0. The isoelectric points and molecular masses were 4.8 and 45 kDa for xylanase and 4.2 and 150 kDa for beta-xylosidase, respectively. Xylanase was stable at 60 degrees C for 24 h, whereas it showed a half life at 70 degrees C of 24 h and at 80 degrees C for 50 min. beta-xylosidase activity did not decrease after 1 h at 60 degrees C. Km of xylanase for xylan was 1.6 mg/ml, Km of beta-xylosidase for p-nitrophenyl-beta-D-xylopyranoside was 0.5 mM and for o-nitrophenyl-beta-D-xylopyranoside was 1.28 mM. The action of two enzymes on xylan gave only xylose.

Xylanase and mannanase enzymes from Streptomyces galbus NR and their use in biobleaching of softwood kraft pulp

Enzymatic pretreatment of softwood kraft pulp was investigated using xylanase and mannanase, singly or in combination, either sequentially or simultaneously. Enzymes were obtained from Streptomyces galbus NR that had been cultivated in a medium, containing either xylan of sugar cane bagasse or galactomannan of palm-seeds, when they were used as sole carbon sources from local wastes in fermentation media. No cellulase activity was detected. Incubation period, temperature, initial pH values and nature of nutritive constituents were investigated. Optimum production of both enzymes was achieved after 5 days incubation on a rotary shaker (200 rpm) at 35 degrees C and initial pH 7.0. Partial purification of xylanase and mannanase in the cultures supernatant were achieved by salting out at 40-60 and 60-80% ammonium sulphate saturation with a purification of 9.63- and 8.71-fold and 68.80 and 62.79% recovery, respectively. The xylanase and mannanase from S. galbus NR have optimal activity at 50 and 40 degrees C, respectively. Both enzymes were stable at a temperature up to 50 degrees C. Xylanase and mannanase showed highest activity at pH 6.5 and were stable from 5.0 to 8.0 and from 5.5 to 7.5, respectively. The partial purified enzymes preparations of xylanase and mannanase enzymes showed high bleaching activity, which is an important consideration for industry. Xylanase was found to be more effective for paper-bleaching than mannanase. When xylanase and mannanase were dosed together (simultaneously), both enzymes were able to enhance the liberation of reducing sugars and improve pulp bleachability, possibly as a result of nearly additive interactions. The simultaneous addition of both enzymes was more effective in pulp treatment than their sequential addition.

Purification and characterization of enzymes exhibiting beta-D-xylosidase activities in stem tissues of Arabidopsis

This work describes the purification and characterization of enzymes that exhibit beta-d-xylosidase activity in stem tissues of Arabidopsis. This is the first detailed investigation that concerns the characterization of catalytic properties and sequence identity of enzymes with beta-D-xylosidase activities in a dicotyledonous plant. Three different enzymes, ARAf, XYL4, and XYL1 with apparent molecular masses of 75, 67, and 64 kD, respectively, were purified to homogeneity. ARAf was identified as a putative alpha-L-arabinofuranosidase, and XYL4 and XYL1 as putative beta-D-xylosidases using matrix-assisted laser-desorption ionization time of flight. ARAf belongs to family 51 and XYL4 and XYL1 to family 3 of glycoside hydrolases. ARAf and XYL1 have highest specificity for p-nitrophenyl-alpha-L-arabinofuranoside and XYL4 for p-nitrophenyl-beta-D-xylopyranoside and natural substrates such as xylobiose and xylotetraose. XYL4 was shown to release mainly D-Xyl from oat spelt xylan, rye arabinoxylan, wheat arabinoxylan, and oligoarabinoxylans. ARAf and XYL1 can also release D-Xyl from these substrates but less efficiently than XYL4. Moreover, they can also release L-Ara from arabinoxylans and arabinan. Overall, the results indicate that XYL4 possesses enzymatic specificity characteristic for a beta-D-xylosidase, while ARAf and XYL1 act as bifunctional alpha-L-arabinofuranosidase/beta-D-xylosidases. Analysis of the activity of these three enzymes in stem tissues at different stages of development has shown that young stems possess the highest activities for all three enzymes in comparison to the activities of the enzymes present in stems at older stages of development. High enzyme activities are most likely related to the necessary modifications of cell wall structure occurring during plant growth.

Streptomyces lividans and Brevibacterium lactofermentum as heterologous hosts for the production of X22 xylanase from Aspergillus nidulans

The Aspergillus nidulans gene xlnA coding for the fungal xylanase X22 has been cloned and expressed in two heterologous bacterial hosts: Streptomyces lividans and Brevibacterium lactofermentum. Streptomyces strains yielded 10 units/ml of xylanase when the protein was produced with its own signal peptide, and 19 units/ml when its signal peptide was replaced by the one for xylanase Xys1 from Streptomyces halstedii. B. lactofermentum was also able to produce xylanase X22, affording 6 units/ml upon using either the Aspergillus xlnA signal peptide or Streptomyces xysA. These production values are higher than those previously reported for the heterologous expression of the A. nidulans xlnA gene in Saccharomyces cerevisiae (1 unit/ml). Moreover, the X22 enzyme produced by Streptomyces lividans showed oenological properties, indicating that this Streptomyces recombinant strain is a good candidate for the production of this enzyme at the industrial scale.

Purification and biochemical properties of a thermostable xylose-tolerant β-D-xylosidase from Scytalidium thermophilum

The thermophilic fungus Scytalidium thermophilum produced large amounts of periplasmic beta- D-xylosidase activity when grown on xylan as carbon source. The presence of glucose in the fresh culture medium drastically reduced the level of beta- D-xylosidase activity, while cycloheximide prevented induction of the enzyme by xylan. The mycelial beta-xylosidase induced by xylan was purified using a procedure that included heating at 50 degrees C, ammonium sulfate fractioning (30-75%), and chromatography on Sephadex G-100 and DEAE-Sephadex A-50. The purified beta- D-xylosidase is a monomer with an estimated molecular mass of 45 kDa (SDS-PAGE) or 38 kDa (gel filtration). The enzyme is a neutral protein (pI 7.1), with a carbohydrate content of 12% and optima of temperature and pH of 60 degrees C and 5.0, respectively. beta- D-Xylosidase activity is strongly stimulated and protected against heat inactivation by calcium ions. In the absence of substrate, the enzyme is stable for 1 h at 60 degrees C and has half-lives of 11 and 30 min at 65 degrees C in the absence or presence of calcium, respectively. The purified beta- D-xylosidase hydrolyzed p-nitrophenol-beta- D-xylopyranoside and p-nitrophenol-beta- D-glucopyranoside, exhibiting apparent K(m) and V(max) values of 1.3 mM, 88 micromol min(-1) protein(-1) and 0.5 mM, 20 micromol min(-1) protein(-1), respectively. The purified enzyme hydrolyzed xylobiose, xylotriose, and xylotetraose, and is therefore a true beta- D-xylosidase. Enzyme activity was completely insensitive to xylose, which inhibits most beta-xylosidases, at concentrations up to 200 mM. Its thermal stability and high xylose tolerance qualify this enzyme for industrial applications. The high tolerance of S. thermophilum beta-xylosidase to xylose inhibition is a positive characteristic that distinguishes this enzyme from all others described in the literature.

Rational affinity purification of native Streptomyces family 10 xylanase

Xylanase SoXyn10A from Streptomyces olivaceoviridis E-86 comprises a family 10 catalytic module linked to a family 13 carbohydrate-binding module (SoCBM13). The SoCBM13 has a beta-trefoil structure, with binding sites in each subdomain (alpha, beta and gamma). Subdomain alpha, but not subdomains beta and gamma, binds tightly to lactose. It was, therefore, thought that immobilized lactose could be used for the affinity purification of SoXyn10A. Lactosyl-Sepharose was prepared and tested as an affinity matrix. SoXyn10A produced from the cloned xyn10A gene by Escherichia coli, and native SoXyn10A in culture supernatants from S. olivaceoviridis, were purified to homogeneity in a single step by affinity chromatography using this matrix. This simple purification of SoXyn10A makes the enzyme an attractive candidate for applications requiring xylanase. The CBM also has the potential for use as an affinity tag for the purification of other proteins.

Xylanase mass transfer studies in aqueous two-phase systems using spray and sieve plate columns

Aqueous two-phase systems (ATPSs) have long been used for biomolecule partitioning; these systems offer the possibility of using continuous or semicontinuous extraction processes. They require relatively simple equipment like spray or sieve plate columns that can be adapted for use in ATPSs. The aim of this work was to study the semicontinuous extraction of a model enzyme, xylanase, in spray and sieve plate columns, since, unlike centrifugal contactors, the cost of construction and maintenance of this equipment is low and it is easy to operate. For the spray column, the dispersed phase hold-up and overall mass transfer coefficients K(D) a were evaluated for different column heights and for different superficial velocities of the dispersed phase (light phase). Results indicated that an increase in superficial velocity in the range of 0-0.18 mm/s of the dispersed phase had a positive effect on K(D) a and on hold-up in all column heights studied, 75, 161 and 246 mm. For the same superficial velocity of the dispersed phase, the larger the hold-up was, the shorter the column. For the sieve plate column, the effects of the superficial velocity of the dispersed phase and the number of plates were also studied. Results showed that the K(D) a and hold-up increased with an increase in both parameters. The selectivity of separation of xylanase and BSA (model contaminant) was very high, since 60% of the enzyme was extracted in the light phase, whereas no significant amount of BSA was extracted. The possibility of using the sieve plate column in continuous operation for enzyme extraction was studied because previous work had only addressed the semicontinuous extraction of enzyme. The residence time distribution of the PEG phase using different superficial velocities of the salt phase was studied in continuous operation. The time required to reach the steady state was 40 min, and 70% of the xylanase was recovered. It was found that the Modified Power Spline software was well adjusted to the experimental results.

Two endoxylanases active and stable at alkaline pH from the newly isolated thermophilic fungus, Myceliophthora sp. IMI 387099

Two extra-cellular endoxylanases (Xyl Ia and Ib) were purified to homogeneity from the newly isolated thermophilic fungus, Myceliophthora sp. IMI 387099. Xyl Ia and Ib, having a molecular mass of approximately 53 kDa and pI of 5.2 and 4.8, respectively, were optimally active at 75 degrees C and at pH 6.0. They were stable at pH 9.2 at 60 degrees C for 2 h, but less stable at pH 6.0 and above 50 degrees C. Mg+2, Zn+2, Ca+2, Co+2 and DTT increased their activity by 1.5-3.0-folds, while SDS and NBS completely inhibited their activity. Both xylanases were active on pNPX and pNPC, but their activity on pNPC was three times higher than that on pNPX. Xyl Ia was more active than Xyl Ib on pNP-alpha-L-Arap, while the latter preferred pNP-alpha-L-Araf. Both xylanases showed two to four times higher activity on rye and wheat arabinoxylans than on birchwood xylan, but Xyl Ib was more active than Xyl Ia on oat spelt xylan. Wheat insoluble pentosan was a good substrate for Xyl Ia, while Xyl Ib preferred wheat soluble arabinoxylan. Xyl Ia had lower Km and higher kcat/Km ratios than Xyl Ib towards all three xylans tested. Both xylanases degraded X4-X6 in an endo-fashion and catalysed hydrolysis and trans-xylosylation reactions. HPLC and LC/MS analysis showed that Xyl Ia and Ib released the unsubstituted X2-X6 as well as mono and di-methyl glucuronic acid substituted X3 and X2 from arabinoxylans.

Purification and characterization of a β-xylosidase from potatoes (Solanum tuberosum)

Potatoes are a cheap and easily available source for the preparation of beta 1,2-xylosidase. The soluble enzyme was purified from potato tubers by ammonium sulfate precipitation, hydrophobic interaction chromatography, affinity gel blue chromatography, ion exchange and size exclusion chromatography yielding a glycoprotein with a molecular weight of 39-40 kDa, an isoelectric point of 5.1 and a typical plant N-glycosylation pattern. The enzyme releases xylose residues beta1,2-linked to the beta-mannose of an N-glycan core, if the 3-position of this mannose is not occupied. It showed an optimal enzymatic activity at pH 4.0-4.5 and at a temperature of 50 degrees C. The activity was reduced in the presence of Ni(2+) and Cu (2+) and slightly increased by the addition of Mn(2+) or Ca(2+). At 37 degrees C the cleavage of xylose from p-nitrophenyl-beta-xylopyranoside or appropriate pyridylaminated N-glycans was proportional to the time of incubation over a period of 8 h and increased with time for at least 24 h. N-Methoxycarbonylpentyl-1,5-dideoxy-1,5-iminoxylitol inhibits the enzyme effectively. Sequencing of the N-terminus showed a high homology to a number of isoforms of patatin, the main protein of potato tubers. This enzyme will be an important tool for the analysis of N-glycans and in the modification of N-glycans for immunological studies.

A xylan-degrading strain of Sulfolobus solfataricus: isolation and characterization of the xylanase activity

Two strains (O(alpha) and X(2)) of the hyperthermophilic crenarchaeon Sulfolobus solfataricus strain MT4 were selected and isolated for their ability to grow on xylan. O(alpha) and X(2), grown on media containing oat spelt xylan and birchwood xylan as the sole nutrient source, respectively, produced the same thermostable xylanase that was demonstrated to be inducible in xylan cultures. In an oat spelt medium, S. solfataricus O(alpha) underwent interesting morphological changes in the cell envelope, exhibiting mobile appendages not present in the typical coccal shape. The enzyme was prevalently membrane associated and showed a molecular mass of approximately 57.0 kDa. It was also highly thermostable, with a half-life of 47 min at 100 degrees C, and exhibited an optimal temperature and pH of 90 degrees C and 7.0, respectively. Xylo-oligosaccharides were the enzymatic products of xylan hydrolysis, and the smallest degradation product was xylobiose, thus indicating that the enzyme was an endoxylanase. The enzyme was able to bind weakly to crystalline cellulose (Avicel) and more strongly to insoluble xylan in a substrate amount-and temperature-dependent manner.

Selective precipitation and recovery of xylanase using surfactant and organic solvent

The selective precipitation of xylanase from an aqueous phase containing mixtures of xylanase and cellulase was studied using an ionic surfactant as precipitating ligand and a polar organic solvent as recovery solvent. Of four ionic surfactants tested, sodium di-(2-ethylhexyl) sulfosuccinate (AOT) showed a complete removal of xylanase at pH 4.5. The recovery of xylanase from the xylanase-AOT complex was a strong function of the type and the volume of the polar solvent and of the concentration of sodium acetate buffer in the final aqueous solution used to solubilize the recovered xylanase. With ethanol as a recovery solvent, a recovery of xylanase activity of 78 +/- 10% was obtained. The cellulase activity in the recovered xylanase was below the detection limit. The results demonstrate that an ionic surfactant can recover enzymes from aqueous solutions without loss in their activity.

Characterization of expression, and cloning, of beta-D-xylosidase and alpha-L-arabinofuranosidase in developing and ripening tomato (Lycopersicon esculentum Mill.) fruit

Modifications to the cell wall of developing and ripening tomato fruit are mediated by cell wall-degrading enzymes, including a beta-d-xylosidase or alpha-l-arabinofuranosidase, which participate in the breakdown of xylans and/or arabinoxylans. The activity of both enzymes was highest during early fruit growth, before decreasing during later development and ripening. Two beta-d-xylosidase cDNAs, designated LeXYL1 and LeXYL2, and an alpha-l-arabinofuranosidase cDNA, designated LeARF1, were obtained. Accumulation of mRNAs for beta-d-xylosidase and alpha-l-arabinofuranosidase was examined during fruit development and ripening. LeARF1 and LeXYL2 genes were relatively highly expressed during fruit development and decreased after the onset of ripening. By contrast, LeXYL1 was not expressed during fruit development, but was expressed later, particularly during over-ripening. The expression of all three genes was also followed in ripening-impaired mutants, Nr, Nr2, nor, and rin of cv. Ailsa Craig fruit. LeXYL2 mRNA was detected in the ripe fruits of all the mutants and its abundance was similar to that in mature green wild-type fruit. By contrast, LEXYL1 mRNA was expressed only in the ripe fruits of the Nr mutant, suggesting that the two beta-d-xylosidase genes are subject to distinct regulatory control during fruit development and ripening. LeARF1 mRNA was detected in ripe fruits of Nr2, nor and rin, and not in ripe fruit of the Nr mutant. The accumulation of LeARF1 in ripe fruit was restored by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, while 1-MCP had no effect on the expression of LeXYL1 or LeXYL2. This suggests that LeARF1 expression is subject to negative regulation by ethylene and that the two beta-d-xylosidase genes are independent of ethylene action.