Effect of N-glycosylation on enzymatic properties of β-glucosidase from Talaromyce leycettanus

Abstract:

[Objective] To investigate the effect of N-glycosylation on the enzymatic properties of β-glucosidase Bgl3A from Talaromyce leycettanus. [Methods] Site-directed mutagenesis was conducted to construct three N-glycosylation-removing mutants T44A, S228A and S299A, and the gene products were expressed in Pichia pastoris GS115. [Results] In comparison with wild type Bgl3A, the mutant S228A was low in protein secretion, with trace activity against pNPG, while mutants T44A and S299A showed similar optimal pH and temperature, i.e. pH 4.0 and 75 ℃, but had higher T_m values and greater thermostability at 70℃. When using pNPG as the substrate, mutants S299A and T44A had decreased catalytic efficiencies (k_cat/K_m) of 14.5% and 70%, respectively; for cellobiose, T44A retained almost the same catalytic efficiency, while S299A showed an improvement of 1.1-fold. [Conclusion] N-glycosylation modification at different sites of Bgl3A had different effect on the secretion and enzymatic properties. Among them, S228 is essential for maintaining the expression and function of the enzyme, whereas S299 can increase the enzyme thermostability and catalytic efficiency on cellobiose.