Biochemical properties of a novel glycoside hydrolase family 1 β-glucosidase (PtBglul) from Paecilomyces thermophila expressed in Pichia pastoris

摘要

A novel p-glucosidase gene {PtBglu I) from the thermophilic fungus, Paecilomyces thermophila, was cloned and expressed in Pichia pastoris. PtBglu i contained an open reading frame of 1440-bp nucleotides and encoded a protein of 479 amino acids which showed significant similarity to other fungal p-glucosidases from glycoside hydrolase (GH) family 1. The recombinant P-glucosidase (PtBglul) was secreted at high level of 190.2 U mL~(-1) in high cell density fermentor (5 L). PtBglul was purified to homogeneity, and was found to be a glycoprotein with molecular mass of 56.7 kDa. The purified PtBglul showed optimum catalytic activity at pH 6.0 and 55 °C. The enzyme exhibited broad substrate specificity with highest activity toward pNP-p-D-glucopyranoside, followed by pNP-P-D-galactopyranoside and cellobiose. The K_m values for pNP-P-D-glucopyranoside, cellobiose, gentiobiose and salicin were 0.55 mM, 1.0 mM, 1.74 mM and 6.85 mM, respectively. These properties make PtBglul a potential candidate for various industrial applications.