Studies On Gene Cloning, Expression And Enzyme Characterization Of A Xylanase From Saccharomonospora Viridis

β-Xylanases is endo-wise glycosyl hydrolase which catalyzes random hydrolysis of β-1,4-xylosidic linkages. It is crucial hemicellulases and produced mainly by microorganisms, plants and lower animals. β-Xylanases has been widely used in many industry processes, such as pulp and paper, foodstuff, animal feed, pharmacy, energy and environmental protection. In this panper a xylanase gene, designated SvixynlOA, was cloned from actinomycetes Saccharomonospora viridis and the gene expression product was characterized.Gene SvixynlOA contains1,374bp and encodes a polypeptide of457amino acids composed of a glycoside hydrolase family10catalytic domain with a putative signal peptide, a short Gly-rich linker and a family2carbohydrate-binding module （CBM）. The deduced amino acid sequence of SviXynlOA shared the highest identity （57%） with a hypothetical xylanase from Streptomyces lividans TK24（ZP₀5528201）. A recombinant His-tagged xylanase, SviXynlOA was expressed in Escherichia coli BL21and purified. The optimum pH and temperature for SviXyn10A is8.0and60℃. Compared with thermophilic and mesophilic counterparts, SviXynlOA was more active at high temperatures, retaining>63%of its maximum activity at65-70℃and-40%even at80℃. It had broad pH adaptability （>35%activity at pH5.0-11.0） and alkali-tolerance （>70%activity after incubation at pH8.0-11.0for1h at37℃）, and was highly thermostable （>75%activity after incubation at70℃for3h at pH8.0）.It is the first alkali-tolerant thermostable xylanase reported from Saccharomonospora. These favorable properties make SviXyn10A a good candidate for the application in pulp and paper industries.