Expression of Trichoderma reesei and Trichoderma viride xylanases in Escherichia coli

Efficient hydrolysis of hemicellulose by a Fusarium graminearum xylanase blend produced at high levels in Escherichia coli

A Fusarium graminearum-based enzyme blend for the efficient hydrolysis of hemicellulose, a crucial step for competitive bioethanol production, is described. The heretofore-uncharacterized endo-1,4-beta-xylanase (XylD), 1,4-beta-xylosidase (XyloA), and bifunctional xylosidase/arabinofuranosidase (Xylo/ArabA) were produced at high levels in Escherichia coli (10-38 mg/l). They displayed compatible pH and temperature-dependences, allowing their utilization for simultaneous substrate digestions. Monosaccharide analysis indicated a strong positive synergism between the enzymes during the degradation of oat spelt xylan. Two units of each protein catalyzed the release of 61% and 15% of the total amount of available d-xylose and l-arabinose, respectively, in only 4 h. The detailed cooperative mechanism of the three hydrolases was elucidated by polysaccharide analysis using carbohydrate gel electrophoresis (PACE) and the enzymes were shown to be suitable for the partial hydrolysis of pretreated crude plant biomass.

Mechanism of stabilization of Bacillus circulans xylanase upon the introduction of disulfide bonds

The introduction of disulfide bonds has been used as a strategy to enhance the stability of Bacillus circulans xylanase. The transition temperature of the S100C/N148C (DS1), V98C/A152C (DS2), and A1GC/G187,C188 (cXl) in comparison to the wild type was increased by 5.0, 4.1 and 3.8 degrees C, respectively. Interestingly, a combination of two disulfide bonds of DS1 and cXl (cDS1, circular disulfide 1) led to a 12 degrees C increase in the transition temperature. Importantly, an increase in the melting point and DeltaDeltaG values of the cDS1 mutant was cooperative. These results suggest that the mechanism of stabilization by disulfide bonds under irreversible denaturation condition is achieved through: (1) a change in the rate-limiting step on the denaturation pathway; (2) destabilizing the unfolded state without affecting the relative rate constants on the denaturation pathway (like cXl mutant); and (3) or combination of the two (cDS1 mutant).

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.

Xylanases from fungi: properties and industrial applications

Xylan is the principal type of hemicellulose. It is a linear polymer of beta-D-xylopyranosyl units linked by (1-4) glycosidic bonds. In nature, the polysaccharide backbone may be added to 4-O-methyl-alpha-D-glucuronopyranosyl units, acetyl groups, alpha-L-arabinofuranosyl, etc., in variable proportions. An enzymatic complex is responsible for the hydrolysis of xylan, but the main enzymes involved are endo-1,4-beta-xylanase and beta-xylosidase. These enzymes are produced by fungi, bacteria, yeast, marine algae, protozoans, snails, crustaceans, insect, seeds, etc., but the principal commercial source is filamentous fungi. Recently, there has been much industrial interest in xylan and its hydrolytic enzymatic complex, as a supplement in animal feed, for the manufacture of bread, food and drinks, textiles, bleaching of cellulose pulp, ethanol and xylitol production. This review describes some properties of xylan and its metabolism, as well as the biochemical properties of xylanases and their commercial applications.