Site-saturation mutagenesis for β-glucosidase 1 from Aspergillus aculeatus to accelerate the saccharification of alkaline-pretreated bagasse.

Aspergillus aculeatus β-glucosidase 1 (AaBGL1) is one of the best cellobiose hydrolytic enzymes without transglycosylation products, among β-glucosidase from various origins, for use in cellulosic biomass conversion with Trichoderma cellulases. However, in our previous report, it was demonstrated that AaBGL1 has lower catalytic efficiency toward cellobiose, which is a major end product from cellulosic biomasses by Trichoderma reesei cellulases, than do gentiobiose and laminaribiose. Thus, we expected that there is room to enhance cellobiose hydrolytic activity of AaBGL1 by increasing catalytic efficiency (k /K ) up to that of gentiobiose or laminaribiose for accelerating the saccharification of cellulosic biomasses, and we performed site-saturation mutagenesis targeting nine amino acids supposed to constitute subsite +1 of AaBGL1.

Characterization of β-glucosidase 1 accelerating cellulose hydrolysis with cellulase system.

β-glucosidase 1 (AaBGL1), which promotes cellulose hydrolysis by cellulase system, was characterized and compared some properties to a commercially supplied orthologue in (AnBGL) to elucidate advantages of recombinant AaBGL1 (rAaBGL1) for synergistic effect on enzymes. Steady-state kinetic studies revealed that rAaBGL1 showed high catalytic efficiency towards β-linked glucooligosaccharides. Up to a degree of polymerization (DP) 3, rAaBGL1 prefered to hydrolyze β-1,3 linked glucooligosaccharides, but longer than DP 3, preferred β-1,4 glucooligosaccharides (up to DP 5).