Identification and Functional Analysis of a Gene Encoding β-Glucosidase from the Brown-Rot Basidiomycete Fomitopsis palustris

The brown-rot basidiomycete Fomitopsis palustris is known to degrade crystalline cellulose (Avicel) and produce three major cellulases, exoglucanases, endoglucanases, and beta-glucosidases. A novel P-glucosidase designated as Cel3A was identified from E palustris grown at the expense of Avicel. The deduced amino acid sequence of Cel3A showed high homology with those of other fungal beta-glucosidases that belong to glycosyl hydrolase (GH) family 3. The sequence analysis also indicated that Cel3A contains the N- and C-terminal domains of GH family 3 and Asp-209 was conserved as a catalytic nucleophile. The cloned gene was successfully expressed in the yeast Pichia pastoris and the recombinant protein exhibited beta-glucosidase activity with cellobiose and some degree of thermostability. Considering the size and sequence of the protein, the beta-glucosidase identified in this study is different from the protein purified directly from F palustris in the previous study. Our results suggest that the fungus possesses at least two beta-glucosidase genes.