Characterization of cyclodextrin glycosyltransferase of the same gene expressed from Bacillus macerans, Bacillus subtilis, and Escherichia coli.

The plasmid pHG contains a cyclodextrin glycosyltransferase (CGTase) gene (cgt) derived from Bacillus macerans. Two transformants, Bacillus subtilis (pHG) and Escherichia coli (pHG), were found to produce CGTases with the same primary structure as the enzyme from B. macerans. However, the β-cyclodextrin coupling activity of the CGTase from E. coli (pHG) was 14-fold higher than that of the enzymes from the other strains. By contrast, no differences in α-cyclodextrin coupling activities were observed among these CGTases. CGTase from E. coli (pHG) was found to be less thermostable than the other CGTases. When the CGTase produced by B. subtilis was treated with increasing urea concentrations (10−1000 mM) to promote increasing degrees of protein unfolding, a bell-shaped β-cyclodextrin coupling activity profile was obtained. Subtle differences in the conformation of the CGTase produced by E. coli are therefore proposed to be responsible for the markedly increased β-cyclodextrin coupling activity of this enzyme....