Cloning of a Gene Encoding β-Glucosidase from Chaetomium thermophilum CT2 and Its Expression in Pichia pastoris

A new thermostable β-glucosidase gene (bgl) from Chaetomium thermophilum CT2 was cloned, sequenced and expressed. The full-length DNA of bgl was 3,101 bp and included three introns. The full-length cDNA contained an open reading frame of 2,604-bp nucleotides, encoding 867 amino acids with a potential secretion signal. The C. thermophilum CT2 β-glucosidase gene was functionally expressed in Pichia pastoris. The purified recombinant β-glucosidase was a 119-kDa glycoprotein with an optimum catalytic activity at pH 5.0 and 60°C. The enzyme was stable at 50°C, and retained 67.7% activity after being kept at 60°C for 1 h; the half-time of the enzyme at 65°C was approximately 55 min, and even retained 29.7% activity after incubation at 70°C for 10 min.