Endo-β-galactosidase

Related Reading

Galactosidase refers to a class of enzymes that hydrolyze substances containing galactosidic bonds, such as lactose (lactose is a disaccharide formed by dehydration and condensation of one molecule of glucose and one molecule of galactose). Mainly divided into α-galactosidase and β-galactosidase. Alpha-galactosidase catalyzes the hydrolysis of alpha-galactosidic bonds, which can transform and decompose the anti-nutritional factors alpha-galactosides in feed and soybean foods, and improve their nutritional content. In addition, the enzyme also has certain applications in pharmacy, thickener treatment and paper industry. β-Galactosidase not only has more and more uses in the food industry, but also plays an important role in biotechnology fields such as genetic engineering, enzyme engineering, protein engineering, etc., and has begun to be widely used in medicine and other fields.

Features

Alpha-galactosidase is an exoglycosidase that catalyzes the hydrolysis of alpha-galactosidic bonds. Because it can decompose melibiose, it is also called melibiase. It can catalyze the hydrolysis of alpha-galactosidic bonds. This feature makes it useful for improving and eliminating anti-nutrients in feed and soy foods. In addition, it can achieve B→O blood type conversion in the medical field, prepare universal blood, and also play an important role in the enzyme replacement therapy of Fabry disease. α-Galactosidase can also act on complex polysaccharides, glycoproteins and glycosphingoses containing α-galactosidic bonds. Certain α-galactosidase enzymes also have a transgalactosyl function when the substrate concentration is highly enriched. Using this feature, they can be used in the synthesis of oligosaccharides and the preparation of cyclodextrin derivatives. The development of neutrophilic or pH-stable α-galactosidase and the search for microorganisms or plants with high enzyme production have become a research focus in recent years. Many heat-resistant α-galactosidase enzymes have gradually attracted wide interest from scientists due to their particularities. They hope to use their thermal stability to play a greater value in industry, as well as to show a wider range in the fields of science and technology and medicine.

β-galactosidase

β-galactosidase belongs to glycoside hydrolase, and there are many microbial sources. In addition to hydrolytic activity, some sources of β-galactosidase also have transglycosylation activity. Enzymes from different sources have different characteristics, such as the optimum pH, optimum temperature, and kinetic constant Km of the enzyme. In addition, the source of enzymes is different, such as Kluyveromyces, Aspergillus, Bacillus, Streptococcus and Cryptococcus, and different reaction conditions, such as temperature and pH, the degree of polymerization, yield and formation of the enzyme reaction to synthesize galacto-oligosaccharides.

Figure 1. Structure of β-galactosidase.

Properties

β-galactosidase is coded by β-galactosidase gene (LacZ gene), which is a tetramer composed of 4 subunits, which generally catalyzes the decomposition of lactose into one molecule of glucose and one molecule of galactose. The protein sequences of β-galactosidase extracted from different species have high homology and similarity. The molecular mass of β-galactosidase is between 100 and 850 ku, of which the β-galactosidase of E. coli has the largest molecular mass, which is 520-850 ku. Beta-galactosidase genes from various sources have been cloned.

Mechanism of action

In addition to catalyzing the hydrolysis of β-galactosidic bonds in β-galactosidase compounds, β-galactosidase also has the function of converting galactosyl groups. Early studies have shown that the active site on β-galactosidase has two functional groups: Cys sulfhydryl and His imidazole, which play an important role in the hydrolysis of lactose by β-galactosidase. It is speculated that the sulfur group can be used as a generalized acid to protonate the oxygen atom of galactosides, while the imidazole group can be used as a nucleophile to attack the nucleophilic center on the first carbon atom of the galactose molecule to form a carbon-hydrogen bond Covalent intermediates. After being cleaved off the imidazole group, the sulfhydryl anion extracts a proton from the water molecule to form -OH and attack C. Some studies believe that the catalytic mechanism of lactase is similar to that of lysozyme. When the receptor for galactosides is water, hydrolysis occurs; when the receptor is another sugar or alcohol, the transgalactoside effect occurs; if the receptor is lactose, the oligomeric half of trisaccharide lactose.

Applications

The research hotspots of β-galactosidase application mainly focus on immobilization, production of oligosaccharides and the use of genetic engineering technology to produce lactase.

The application of β-galactosidase in food processing mainly includes the following aspects:

• Solve the problem of dairy consumption in patients with lactose intolerance.
• Used to improve the sweetness of dairy products.
• Prevent crystallization of dairy products when freezing.
• Production of galactooligosaccharides.

Reference

1. Davies, G.; et al. Structures and mechanisms of glycosyl hydrolases. Structure. 1995, 3 (9): 853–59.