Cyclodextrin glycosyltransferase variants experience different modes of product inhibition

Maltose binding site 2 mutations affect product inhibition of Bacillus circulans STB01 cyclodextrin glycosyltransferase

The efficiency of enzymatic cyclodextrin production using cyclodextrin glycosyltransferases (CGTases) is limited by product inhibition. In this study, maltose binding site 2 (MBS2) of the β-CGTase from Bacillus circulans STB01 was modified to decrease product inhibition. First, two point mutants were prepared at position 599 (A599V and A599N). Then, two double mutants incorporating alanine at position 633 (A599N/Y633A and A599V/Y633A) were prepared. Finally, the entire MBS2 region was replaced by that of the α-CGTase from Paenibacillus macerans JFB05-01 to form multipoint mutant MBS2 β → α. All five mutants exhibited mixed-type product inhibition, although both the competitive and uncompetitive components of this inhibition were decreased. The total cyclization activities of A599N, A599V and A599V/Y633A were 15.6%, 76.8% and 70.9% lower than that of the wild-type, respectively, while that of A599N/Y633A was 22.4% higher. Among the mutants, only MBS2 β → α showed catalytic efficiency (k_cat/K_m) comparable with that of the wild-type. Moreover, A599N, A599N/Y633A and MBS2 β → α produced cyclodextrin yields 13.1%, 15.8% and 19.7% greater than that of the wild-type, respectively. These results suggest that A599N, A599N/Y633A and MBS2 β → α may be more suitable than the wild-type for cyclodextrin production.

Identification, cloning and expression analysis of an alpha-CGTase produced by stain Y112

Cyclodextrin glycosyltransferase (CGTase) is an enzyme able to convert starch and other substrates into cyclodextrins (CDs). A marine strain Y112 producing α-CGTase was identified as Bacillus agaradhaerens Y112 by physiological and biochemical characterization, and 16S rDNA analysis. The gene coding for α-CGTase was cloned, sequenced and expressed in Escherichia coli BL21 (DE3) cells. Recombinant α-CGTase was purified in one-step chromatographic separation and its purity evaluated by SDS-PAGE, showing the presence of one band with a molecular mass of about 92 kDa. Additionally, enzymatic capability was analyzed by measuring the starch conversion, and resulted in about 45% of CDs obtained after 6 h of cyclodextrin reaction. Of these CDs, mainly α-CD was produced (70% of the total CDs yield), suggesting the potential of this CGTase for industrial applications.