Glycoside hydrolase family 2 exo-β-1,6-galactosidase LpGal2 from Lactobacillus plantarum: Cloning, expression, and enzymatic characterization

Lactobacillus plantarum is a useful microorganism that metabolizes galactose-containing polysaccharides. Genome analysis has shown that L. plantarum contains four β-galactosidase-related genes. Here, we cloned the β-galactosidase gene that encodes the glycoside hydrolase family 2 (GH2) enzyme LpGal2. Recombinant LpGal2 (rLpGal2, 72 kDa) is a homodimer with maximal enzymatic activity at pH 7.0 and 50 °C. Under these conditions, rLpGal2 hydrolyzes p-nitrophenyl-β-D-galactopyranoside (pNPβGal) with a specific activity of 2.16 × 10−3 U/mg and substrate specificity for β-1,6-galactobiose to produce D-Galactose. In addition, rLpGal2 can also hydrolyze β-1,6-galactan to D-Galactose, whereas other galactose-containing oligosaccharides and polysaccharides tested could not be hydrolyzed. This finding demonstrates that LpGal2 functions as an exo-β-1,6-galactosidase with narrow substrate specificity. To our knowledge, this is the first report of a β-galactosidase derived from L. plantarum with exo-β-1,6-galactosidase activity that has potential application for structure analysis of polysaccharides.