Cloning, heterologus expression and characterization of a thermophilic and salt tolerant GH11 xylanase from Allostreptomyces psammosilenae YIM DR4008T.

Xylanases are used in a wide range of applications such as food, feed, and bioenergy production. Many industrial applications need to be carried out at high temperatures, so it is important to discover new thermophilic xylanases. In this study, a xylanase gene (576 bp), denominated apxyn11a, was obtained from Allostreptomyces psammosilenae YIM DR4008T and was cloned and heterologously expressed in Escherichia coli BL21(DE3). The recombinant xylanase (ApXyn11A) was isolated and purified by Ni2+-affinity chromatography. The molecular weight of recombinant ApXyn11A was 22.7 kDa. Its optimum reaction temperature and pH were 65 °C and 5.6, respectively. It maintained above 95% relative activity after incubation at 55 °C for 120 min and more than 80% residual activity after incubation in pH 4.0-6.0 for 24 h. What more, ApXyn11A exhibited more than 60% relative activity in presence of 3.5 M NaCl. The kinetic parameters Km (0.2 mg/mL), Vmax (2000 μmol/min/mg) and Kcat (755.09 S-1) were determined using corn cob xylan as the substrate. These indicate that ApXyn11A has the properties of small molecular weight, thermophilic, salt and acid tolerance, which predicts the potential use of ApXyn11A in food, feed, paper and bioenergy fields.