Glucosidase is a large class of enzymes in glycoside hydrolase (EC 3.2.1). It is named because it can hydrolyze the glucoside bond and release a molecule of glucose.

Glucosidase has a wide range of sources, and it exists in almost all organisms with cellular structure that use carbohydrates as energy sources. According to the classification of the Carbohydrate-Active enZYmes Database (CAZy) based on the homology of protein crystal structure and the similarity of function, the discovered glycoside hydrolases can be divided into 133 glycosides. Hydrolase family (GH1~GH133). Among them, glucosidases are mainly distributed in glycoside hydrolase families such as GH1, GH3, GH4, GH5, GH9, GH13, GH17, GH30, GH31, GH63, GH97, GH116 and GH122.

1. Classification according to the hydrolysis method
According to the way different glucosidase hydrolyze the oligosaccharide substrate, it can be divided into exo-glucosidase and endo-glucosidase. Exo-glucosidase refers to a glucosidase that hydrolyzes from one end (reducing end or non-reducing end) of an oligosaccharide substrate. The endoglucosidase refers to the glucosidase that hydrolyzes from the middle part of the oligosaccharide substrate.

2. According to the type of hydrolyzed glycosidic bond
Since the glucosidic bond is divided into two types: α-type and β-type, the corresponding glucosidase is called α-glucosidase and β-glucosidase, respectively. According to the specific classification of CAZy, α-glucosidase is mainly distributed in the six families of GH4, GH13, GH31, GH63, GH97 and GH122. The β-glucosidase is mainly distributed in seven families, including GH1, GH3, GH5, GH9, GH17, GH30, and GH116. β-glucosidase is composed of two polypeptide chains, which are chiral in nature, meaning that the two chains are asymmetric and not superimposable. Each chain is composed of 438 amino acids, which constitute a subunit of the enzyme, and each subunit contains an active site. The active site is the position where the enzyme and the substrate bind and the enzymatic reaction may occur. The active site has three potential components: pockets, cracks and tunnels. The bag-like structure facilitates the recognition of monosaccharides such as glucose. The cracks allow sugars to combine to form polysaccharides. The channel allows the enzyme to attach to the polysaccharide and then release the product while still attached to the sugar.

3. Classification according to the configuration of glucose molecules before and after hydrolysis
According to the comparison of whether the configuration of the anomeric carbon in the hydrolyzed glucosyl group changes before and after hydrolysis, glucosidase can be divided into retention glucosidase and flip-glucosidase. The former does not change the configuration of the anomeric carbon of the glucosyl group before and after the hydrolysis process; while the latter will reverse the configuration of the substrate anomeric carbon.

Glucosidase is one of the important members in the carbohydrate metabolism pathway in organisms. β-glucosidase can participate in the metabolism of cellulose and a variety of physiological and biochemical pathways, and α-glucosidase is directly involved in the metabolic pathways of starch and glycogen. Abnormal functions of these enzymes can lead to metabolic diseases. At the same time, these enzymes are also targets of various drugs and inhibitors to regulate the chemical metabolism of sugar in the human body.

Due to its characteristics, glucosidase is mainly used in two aspects:
The hydrolysis and utilization of cellulose: It mainly involves various β-glucosidase and cellulose hydrolysis-related enzymes, with the purpose of turning insoluble cellulose into soluble and easy-to-use small molecular oligosaccharides.

The synthesis of functional oligosaccharides: mainly involves the transglycosidase activity of glucosidase. The purpose is to synthesize functional oligodextran, oligomalto-oligosaccharide, oligo-cello-oligosaccharide and other functional sugars that can be used as prebiotics by glucosidase with transglycosidase activity.

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