Heterologous Expression and Characterization of a GH3 β-Glucosidase from Thermophilic Fungi Myceliophthora thermophila in Pichia pastoris

A novel beta-glucosidase of glycoside hydrolase (GH) family 3 from Myceliophthora thermophila (mtbgl3b) was successfully expressed in Pichia pastoris. The full-length gene consists of 2613 bp nucleotides encoding a protein of 870 amino acids. MtBgl3b showed maximum activity at pH 5.0 and remained more than 70 % relative activity at 3.5-6.0. The enzyme displayed the highest activity at 60 A degrees C and kept about 90 % relative activity for 50-65 A degrees C; besides, the enzyme showed psychrophilic trait and remains 51 % relative activity at 40 A degrees C. MtBgl3b exhibited good stability over a wide pH range of 3.0-10.0 and was thermostable at 60 and 65 A degrees C. The enzyme displayed highest activity towards p-nitrophenyl-beta-d-glucopyranoside (pNPG), followed by p-nitrophenyl-d-cellobioside (pNPC), cellotetraose, cellotriose, cellobiose, and gentiobiose. When using 10 % cellobiose (w/v) as the substrate, the enzyme showed transglycosylation activity to produce the cellotriose. The kinetic parametric of K (m) and V (max) were 2.78 mM and 927.9 mu M mg(-1) min(-1), respectively. Finally, the reaction mode of the enzyme and the substrates were analyzed by molecular docking approach.