A team of Japanese researchers led by Associate Professor Masahiro Nakajima from the Tokyo University of Science (TUS) has identified a new β-galactosidase enzyme in the gut bacterium Bacteroides xylanisolvens. They believe this discovery could pave the way for prebiotic science and food technology advancements. 

Carbohydrate chains, or glycans, are essential sugar-like compounds that contribute to various biological functions in humans, plants, and microorganisms. Among them, galactosides — found in plant cell walls and prebiotic oligosaccharides — play a crucial role in gut health.

Due to their potential health benefits, many of these glycans are also incorporated into processed foods like juice and powdered milk.

β-Galactosidases are enzymes that break down galactosides by releasing galactose, a simple sugar. While these enzymes are commonly found in human gut bacteria such as Bifidobacterium, little has been known about their role in B. xylanisolvens.

The new study indicates that B. xylanisolvens can utilize a diverse range of carbohydrates, which prompted further investigation into its enzymatic functions.

The study, published in Communications Biology, reveals that the newly discovered β-galactosidase specifically targets unique galactose-containing glycans, which may have significant prebiotic properties.

Understanding the mechanisms of this enzyme could enhance its applications in health supplements and functional food development.

“Although there are numerous types of glycans with diverse and complex structures, many glycans still have unknown functionality and potential uses. Since enzymes are essential for the synthesis of glycans, the search for new enzymes is extremely important,” explains Dr. Nakajima.

“Our novel enzyme could be used to synthesize large amounts of unique glycans with prebiotic properties that may be beneficial to human health.”

New enzyme discovery

The scientists discovered that B. xylanisolvens has multiple genes that produce enzymes called β-galactosidases, which help break down certain sugars. Among them, they identified a new enzyme named Bxy_22780. At first, this enzyme didn’t seem to work on natural galactosides.

However, when researchers tested it using special chemical conditions — adding a modified sugar (α-GalF) and either galactose or D-fucose — they found that the enzyme was active. Further testing using nuclear magnetic resonance confirmed that the enzyme produced a specific type of sugar molecule called β-1,2-galactobiose.

Targeting specific sugars

The team then looked more closely at what kinds of sugars Bxy_22780 can break down. They found that it works specifically on galactooligosaccharides (GOS), which are complex sugars often used as prebiotics. 

However, it only targets a specific type of GOS that has a β-1,2-galactosidic bond. Experiments showed that the enzyme is particularly good at breaking down two specific sugars: β-1,2-galactobiose and β-1,2-galactotriose.

To understand why Bxy_22780 is so selective, the scientists studied its structure using X-ray diffraction. They discovered that the enzyme has a special site, called subsite +1, wher it binds to sugars in a very precise way. This explains why it only works on β-1,2-galactooligosaccharides and not other types of sugars.

These findings shed new light on how gut bacteria process carbohydrates and could lead to new developments in prebiotics and functional food products.

“β-1,2-Galactooligosaccharides and the enzymes are rarely reported. Our discovery is a crucial step toward understanding the functions of these unique glycans, whose roles are largely unknown,” says Dr. Nakajima. 

“Furthermore, while there is currently no evidence that β-1,2-galactooligosaccharides possess prebiotic properties, they hold potential in this regard. This enzyme could also open new therapeutic avenues for treating diseases like Chagas disease, caused by a parasite that produces glycans containing these structures.”

“This novel enzyme could, therefore, not only help improve human gut health but also contribute to developing new life-saving drugs.”