Expression and characterization of a cellobiohydrolase (CBH7B) from the thermophilic fungus Thielavia terrestris in Pichia pastoris

Abstract

The gene encoding a cellobiohydrolase 7B (CBH7B) of the thermophilic fungus Thielavia terrestris was identified, subcloned, and expressed in Pichia pastoris. CBH7B encoded 455 amino acid residues with a molecular mass of 51.8 kDa. Domain analysis indicated that CBH7B contains a family 7 glycosyl hydrolase catalytic core but lacks a carbohydrate-binding module. Purified CBH7B exhibited optimum catalytic activity at pH 5.0 and 55 °C with 4-methylumbelliferryl-cellobioside as the substrate and retained 85% of its activity following 24 H incubation at 50 °C. Despite the lack of activity toward microcrystalline substrates, this enzyme worked synergistically with the commercial enzyme cocktail Cellic® CTec2 to enhance saccharification by 39% when added to a reaction mixture containing 0.25% alkaline pretreated oil palm empty fruit bunch (OPEFB). Attenuated total reflectance Fourier transform infrared spectroscopy suggested a reduction of lignin and crystalline cellulose in OPEFB samples supplemented with CBH7B. Scanning electron microscopy revealed greater destruction extent of OPEFB strands in samples supplemented with CBH7B as compared with the nonsupplemented control. Therefore, CBH7B has the potential to complement commercial enzymes in hydrolyzing lignocellulosic biomass.