Our phylogenetic analysis revealed a new T. reesei b-glucosidase,
TrCel3B, belonging to the same cluster as the Aspergillus b-glucosidases,
which exhibit high cellobiase activity (Figs. 1 and S1).
Therefore, cel3b of T. reesei seemed like a good b-glucosidase
candidate for testing expression in S. cerevisiae. Our report is the
first to show such heterologous expression of TrCel3B in
S. cerevisiae. Examination of cellobiase activity of the recombinant
strains using either TrCel3B or AaBGL1 indicated that the recombinant
AaBGL1 showed higher pNPGase activity than that of
TrCel3B (Fig. 3B), revealing that S. cerevisiae INVSc1 expressing
AaBGL1 had higher cellobiose-metabolizing capacity than TrCel3B.
Further characterization also revealed post-translational modifi-
cations, such as glycosylation, in these recombinant proteins, suggesting
structural modifications that could potentially enhance
enzyme activities. Glycosylation of BGLs has been reported previously
in A. aculeatus (47). Although the amount of protein secreted
in AaBGL1 culture was lower than in TrCel3B, the specific activity of
AaBGL1 against pNPGlc or cellobiose was evidently higher than that
of TrCel3B (Table 1). The stability of AaBGL1 was also superior to
TrCel3B under various pH and thermal conditions, prompting us to
select yeast expressing recombinant AaBGL1 for use in the subsequent
SSF process