Molecular Cloning and Expression of the Novel Fungal β-Glucosidase Genes from Humicola grisea and Trichoderma reesei

Abstract

A novel fungal β-glucosidase gene (bgl 4) and its homologue (bgl 2) were cloned from the cellulolytic fungi Humicola grisea and Trichoderma reesei, respectively. The deduced amino acid sequences of H. grisea BGL 4 and T. reesei BGL 2 comprise 476 and 466 amino acids, respectively, and share 73.1% identity. These β-glucosidases show significant homology to plant β-glucosidases belonging to the β-glucosidase A (BGA) family. Both genes were expressed in Aspergillus oryzae, and the recombinant β-glucosidases were purified. Recombinant H. grisea BGL 4 is a thermostable enzyme compared with recombinant T. reesei BGL 2. In addition to β-glucosidase activity, recombinant H. grisea BGL 4 showed a significant level of β-galactosidase activity, while recombinant T. reesei BGL 2 showed weak β-galactosidase activity. Cellulose saccharification by Trichoderma cellulases was improved by the addition of recombinant H. grisea BGL 4.