β-galactosidases, can be used to synthesize galacto-oligosaccharides (GOS) due to the transglycosylating (secondary) activity of these enzymes. Site-directed mutagenesis of a thermoresistant β-galactosidase from Thermotoga maritima has been carried out to study the structural basis of transgalactosylation and to obtain enzymatic variants with better performance for GOS biosynthesis.
Reference: D. Talens-Perales, J. Polaina, and J. Marín-Navarro. "Structural Dissection of the Active Site of Thermotoga maritima β‑Galactosidase Identifies Key Residues for Transglycosylating Activity". J. Agric. Food Chem. 2016, 64, 2917−2924. DOI: 10.1021/acs.jafc.6b00222