Abstract
Xylans are major hemicellulose components of plant cell wall which can be hydrolyzed by xylanolytic enzymes. Three forms of endo-β-1,4-xylanases (XynSW1, XynSW2A, and XynSW2B) produced by thermotolerant Streptomyces sp. SWU10 have been reported. In the present study, we described the expression and characterization of the fourth xylanase enzyme from this bacteria, termed XynSW3. The gene containing 726 bp was cloned and expressed in Escherichia coli. The recombinant enzyme (rXynSW3) was purified from cell-free extract to homogeneity using Ni-affinity column chromatography. The apparent molecular mass of rXynSW3 was 48 kDa. Amino acid sequence analysis revealed that it belonged to a xylanase of glycoside hydrolase family 11. The optimum pH and temperature for enzyme activity were 5.5-6.5 and 50 °C, respectively. The enzyme was stable up to 40 °C and in wide pH ranges (pH 0.6-10.3). Xylan without arabinosyl side chain is the most preferable substrate for the enzyme. By using birch wood xylan as substrate, rXynSW3 produced several oligosaccharides in the initial stage of hydrolysis, and their levels increased with time, demonstrating that the enzyme is an endo-acting enzyme. The major products were xylobiose, triose, and tetraose. The rXynSW3 can be applied in several industries such as food, textile, and biofuel industries, and waste treatment.
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