BgaD-D of Bacillus circulans ATCC 31382 mutant R484S

Beschrijving

The C-terminally truncated β-galactosidase enzyme from Bacillus circulans ATCC 31382 mutant R484S is a member of Glycoside Hydrolase family 2. This enzyme, also known as BgaD-D, is the shortest isoform of the full-length protein BgaD. The microbial enzyme is able to synthesize prebiotic galactooligosaccharides (GOS) and Oligos from lactulose (OsLu). These products are widely used as biocatalyst in the food industry, because of their healthy effect on humans. GOS mixtures mimic the prebiotic effects of the human milk oligosaccharides, and therefore are added to infant formula.

The mutant enzyme displays altered enzyme specificity, leading to new types of GOS products. The GOS mixture produced by the mutant enzyme introduces 14 new structures that were not present in the wild type, 10 of these were never shown before. Indicating the position Arg484 represents a crucial role in the product binding affinity of BgaD-D, the shortest isoform of Bga-D. In contrast with the wild type, the GOS products synthesized by BgaD-D mutant R484S presents a carbohydrate mixture showing a majority of β(1→3) and β(1→4) linked galactose on the reducing glucose residue.  The products contain both linear and branched structures. Some basic structures are further elongated with β(1→3) and β(1→4)-linked galactose residues, resulting in 3,4-disubstituted galactose residues.

Moreover, the B. ciruculans ATCC 31382 mutant R484S is able to synthesize oligosaccharides derived from lactulose (OsLu). Although the yields are rather low compared with GOS production using lactose, the enzyme creates high-value compounds. The relatively short products with mainly dp 2 and dp 3 have a preference for introducing β(1→3) linkages. OsLu may act as prebiotic compounds and are potentially resistant to gut digestion.

Human newborns are capable to produce β-galactosidase enzymes to digest lactose. Nevertheless, the majority of adults have lost the ability to produce these enzymes. This can end up in lactose intolerance, making them incapable to digest dairy products. The lactose could be removed from the milk to solve this problem, and the residual product could be converted to high valuable lactose derivates like GOS.