Characterization of a β-1,4-glucosidase from a newly isolated strain of Pholiota adiposa and its application to the hydrolysis of biomass

The highly efficient β-1,4-glucosidase (BGL)-secreting strain, Pholiota adiposa SKU0714, was isolated and identified based on its morphological features and sequence analysis of internal transcribed spacer (ITS) rDNA. P. adiposa BGL (PaBGL), which contained a carbohydrate moiety, was purified to homogeneity from P. adiposa culture supernatants by 2-step chromatography on DEAE and Sephacryl gel filtration columns. The relative molecular weight of PaBGL was 60kDa by SDS-PAGE or 59kDa by size exclusion chromatography, indicating that the enzyme is a monomer. The pH and temperature optima for hydrolysis were 5.0 and 65°C, respectively. PaBGL showed the highest activity towards p-nitrophenyl-β-d-glucopyranoside (V_max=4390Umgprotein^-1, K_m=2.23molm^-3) and cellobiose (V_max=3460Umgprotein^-1, K_m=5.60molm^-3) ever reported. Its internal amino acid sequences showed homology with hydrolases from the glycoside hydrolase family 3 (GH3), indicating that PaBGL is a member of the GH3 family. The hydrolysis of rice straw using a commercial cellulase, Celluclast^® 1.5L, resulted in a higher saccharification yield with the addition of PaBGL than with Novozyme 188. PaBGL may be a good candidate for applications that convert biomasses to biofuels and chemicals.