LAUSR

Lacto-N-tetraose (LNT) is one of the most important components of human milk oligosaccharides, which has various beneficial health effects. β-Galactosidase is an important enzyme used in dairy processing. The transglycosylation activity of β-galactosidases offers an attractive approach for LNT synthesis. In this study, we reported for the first time the biochemical characterization of a novel β-galactosidase (LzBgal35A) from Lacticaseibacillus zeae. LzBgal35A belongs to glycoside hydrolases (GH) family 35 and shared the highest identity of 59.9% with other reported GH 35 members. The enzyme was expressed as soluble protein in E. coli. The purified LzBgal35A displayed optimal activity at pH 4.5 and 55°C. It was stable within the pH range of 3.5-7.0 and up to 60°C. Moreover, LzBgal35A could catalyze the synthesis of LNT via transferring the galactose residue from o-nitrophenyl-β-galactopyranoside (oNPG) to lacto-N-triose II. Under the optimal conditions, the conversion rate of LNT reached 45.4% (6.4 g/L) within 2 h, which was the highest yield of LNT synthesized through a β-galactosidase-mediated transglycosylation reaction by far. This study demonstrated that LzBgal35A had great potential application in LNT synthesis.