Characterization of a β-galactosidase from Bacillus subtilis with transgalactosylation activity

Microbial beta-galactosidases (EC 3.1.2.23) have applications in the production of galacto-oligosaccharides, which are established prebiotic food ingredients. The p-galactosidase from Bacillus subtilis (YesZ) was expressed as a heterologous protein in Escherichia coil, and presented an optimum activity at pH 6.5 and 40 degrees C. The catalytic constants K-m and V-max of the enzyme were 8.26 mM and 1.42 mu mol . min(-1) . mg-(1) against pNP-beta-D-galactopyranoside, respectively. Structural characterization revealed that YesZ is a homotrimer in solution, and homology modeling suggested that the YesZ conserves a Cys cluster zinc binding site. Flame photometry experiments confirmed the presence of bound zinc in the recombinant enzyme, and YesZ activity was inhibited by 1 mM zinc, copper and silver ions. Transgalactosylation activity of YesZ was observed with the synthetic substrate p-NP-beta-Gal in the presence of a o-xylose acceptor, producing a beta-D-galactopyranosyl-(1 -> 4)-D-xylopyranose disaccharide. Analysis of this disaccharide by MALDI-ToF-MS/MS suggested a beta-1,4 glycosidic linkage between a non-reducing galactose residue and the xylose. The p-galactosidase YesZ from B. subtilis is a candidate for enzymatic synthesis showing favorable thermostability (with residual activity of 50% after incubation at 30 degrees C for 25 h) and transgalactosylation activity. (C) 2018 Published by Elsevier B.V.