Purification, characterization and gene cloning of two forms of a thermostable endo-xylanase from Streptomyces sp. SWU10

Abstract

Two forms of an endo-xylanase were isolated from the culture filtrate of Streptomyces sp. SWU10 that grew on rice straw. The molecular masses of both forms of an enzyme were 31 kDa (XynSW2A) and 44 kDa (XynSW2B). Analysis of internal amino acid sequences of the proteins by liquid chromatography/ion-trap/ time-of flight mass spectrometer (LC/IT/TOF MS) revealed that XynSW2A may be the proteolytic fragment of XynSW2B. Optimal temperature and pH of XynSW2A and XynSW2B were 60 °C and 6.0, respectively. Both forms of the enzyme were stable in a wide pH ranges. More than 80% of the initial activities remained at pH 3-9 (XynSW2A) and 2-9 (XynSW2B) after 16 h of incubation at 4 °C. XynSW2A and XynSW2B were stable up to 80 °C and 60 °C, respectively. Both forms of the enzyme were strongly inhibited by Hg2+ ions. Birch wood xylan, which has no arabinofuranosyl side chains, was the most preferred substrate for both forms. The xynSW2 gene encoding XynSW2B was isolated by in vitro cloning. The coding sequence of xynSW2 gene was 1434 bp in length and encode a polypeptide of 477 amino acid residues. Pfam analysis revealed Glycohydro 10 and Ricinβlectin domains in XynSW2B. The deduced amino acid sequence of XynSW2B exhibited the highest identity with that of a xylanase A of Streptomyces coelicolor A3(2) belong to glycoside hydrolase (GH) family 10. Because of their pH and thermal stabilities, XynSW2A and XynSW2B may have potential application in biofuel industry by using rice straw and can be applied in food, textile industries, and waste treatment. © 2011 Elsevier Ltd. All rights reserved.