Enhancing the production of galacto-oligosaccharides by mutagenesis of Sulfolobus solfataricus β-galactosidase

Galacto-oligosaccharides (GOS), an important class of functional food, are commonly produced from lactose using β-galactosidase. In the present study, β-galactosidase (LacS) from Sulfolobus solfataricus P2 was cloned and site-directed mutagenesis was performed to obtain two mutants, F359Q and F441Y. All of the wild-type enzyme and mutants were expressed in Escherichia coli BL21(DE3) and purified to homogeneity. The enzymatic properties and optimal condition for transglycosylation reaction of the enzymes were investigated in detail. Under their individual optimal conditions, yields of GOS could reach 50.9% for wild-type enzyme, 58.3% for F359Q, and 61.7% for F441Y. In addition, the potential mechanism for this enhancement was analysed.