RESUMO
The recombinant alkalistable and moderately thermostable bifunctional endoglucanase gene (BhCell-Xyl) of polyextremophilic bacterium Bacillus halodurans TSLV1 has been expressed in Pichia pastoris under constitutive GAP as well as inducible AOX promoters. A higher titre of recombinant BhCell-Xyl was attained after induction (4.8 U mL-1) as compared to that of the constitutive production (2.1 U mL-1). The recombinant P. pastoris strains integrated two copies of BhCell-Xyl under AOX and GAP promoters. The pure recombinant BhCell-Xyl is a glycoprotein of 66 kDa, which is optimally active at 60 °C and pH 6.0 and 8.0. Glycosylated BhCell-Xyl exhibits higher thermostability than that of the native enzyme. The analysis of amino acids of BhCell-Xyl revealed that multiple factors are responsible for its thermostability. Kinetics and in silico analysis of the enzyme suggested that BhCell-Xyl has one active site for both endocellulase and endoxylanase activities. The BhCell-Xyl possesses a carbohydrate binding domain and saccharifies lignocellulosic agro-residues to xylo-oligosaccharides and cello-oligosaccharides, suggesting its potential application in generating fermentable sugars from renewable agro-residues for biofuel and fine chemical industries.
