Molecular Cloning and Expression of the Novel Fungal β-Glucosidase Genes from Humicola grisea and Trichoderma reesei1

Abstract

A novel fungal β-glucosidase gene (bgl4) and its homologue (bgl2) were cloned from the cellulolytic fungi Humicola grisea and Trichoderma reesei, respectively. The deduced amino acid sequences of H. grisea BGL4 and T. reesei BGL2 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 BGL4 is a thermostable enzyme compared with recombinant T. reesei BGL2. In addition to β-glucosidase activity, recombinant H. grisea BGL4 showed a significant level of β-galactosidase activity, while recombinant T. reesei BGL2 showed weak β-galactosidase activity. Cellulose saccharification by Trichoderma cellulases was improved by the addition of recombinant H. grisea BGL4.

cellulase, cellulolytic fungi, β-glucosidase, Humicola grisea, Trichoderma reesei