The role of conserved arginine residue in loop 4 of glycoside hydrolase family 10 xylanases

A novel cold-active GH8 xylanase from cellulolytic myxobacterium and its application in food industry

Although xylanase have a wide range of applications, cold-active xylanases have received less attention. In this study, a novel glycoside hydrolase family 8 (GH8) xylanase from Sorangium cellulosum with high activity at low temperatures was identified. The recombinant xylanase (XynSc8) was most active at 50 °C, demonstrating 20% of its maximum activity and strict substrate specificity towards beechwood and corncob xylan at 4 °C with V_max values of 968.65 and 1521.13 μmol/mg/min, respectively. Mesophilic XynSc8 was active at a broad range of pH and hydrolyzed beechwood and corncob xylan into xylooligosaccharides (XOS) with degree of polymerization greater than 3. Moreover, incorporation of XynSc8 (0.05-0.2 mg/kg flour) provided remarkable improvement (28-30%) in bread specific volume and textural characteristics of bread compared to commercial xylanase. This is the first report on a novel cold-adapted GH8 xylanase from myxobacteria, suggesting that XynSc8 may be a promising candidate suitable for bread making.

Improved thermal performance of Thermomyces lanuginosus GH11 xylanase by engineering of an N-terminal disulfide bridge

In order to increase the stability of thermophilic Thermomyces lanuginosus GH11 xylanase, TLX, a disulfide bridge Q1C-Q24C was introduced into the N-terminal region of the enzyme. The apparent temperature optimum shifted upwards at pH 6.5 by about 10°C to 75°C. The resistance to thermal inactivation also increased by about 10°C. The melting temperature measured by CD spectroscopy increased from 66 to 74°C. Therefore the N-terminal disulfide bridge increased both kinetic and thermodynamic stability almost equally. At pH 8 and 70°C, the disulfide bridge increased the enzyme half-life 20-fold in the presence of substrate. In contrast to the situation in acidic-neutral pH, the substrate decreased the thermostability of xylanases in alkaline pH. The upper limit for the performance of the disulfide bridge mutant at pH 9 was 75°C. This study showed that N-terminal disulfide bridges can stabilize even thermostable family GH11 xylanases.

Cloning, sequence analysis, and expression of a gene encoding an endoxylanase from Bacillus halodurans S7

The gene encoding an alkaline active xylanase of Bacillus halodurans S7, containing an open reading frame of 1188 nucleotides encoding 396 amino acids, was cloned and expressed in Escherchia coli. On the basis of sequence similarity, possible -10 and -35, ribosome binding, and transcription terminator regions were identified. Analysis of the deduced amino acid sequence revealed that the protein was a single domain enzyme belonging to family 10 and designated as xyn10A. The calculated molecular mass and isoelectric point (pI) of the mature peptide were 42.6 and 4.5 kDa, respectively. Xylanase activity expressed by the recombinant organism was detected in the cytoplasm, periplasm and the extracellular medium. In an 18-h old culture, about 39% of the xylanase was detected in the medium. The stability and activity profile of the recombinant xylanase was similar to the properties of the enzyme produced by the wild-type organism.