A New ß-Galactosidase from the Antarctic Bacterium Alteromonas sp. ANT48 and Its Potential in Formation of Prebiotic Galacto-Oligosaccharides.

As an important medical enzyme, ß-galactosidases catalyze transgalactosylation to form prebiotic Galacto-Oligosaccharides (GOS) that assist in improving the effect of intestinal flora on human health. In this study, a new glycoside hydrolase family 2 (GH2) ß-galactosidase-encoding gene, galA, was cloned from the Antarctic bacterium Alteromonas sp. ANT48 and expressed in Escherichia coli. The recombinant ß-galactosidase GalA was optimal at pH 7.0 and stable at pH 6.6-7.0, which are conditions suitable for the dairy environment. Meanwhile, GalA showed most activity at 50 °C and retained more than 80% of its initial activity below 40 °C, which makes this enzyme stable in normal conditions. Molecular docking with lactose suggested that GalA could efficiently recognize and catalyze lactose substrates. Furthermore, GalA efficiently catalyzed lactose degradation and transgalactosylation of GOS in milk. A total of 90.6% of the lactose in milk could be hydrolyzed within 15 min at 40 °C, and the GOS yield reached 30.9%. These properties make GalA a good candidate for further applications.