Β-Glucosidase
β-Glucosidase is an enzyme that catalyses the following reaction:
Structure
β-Glucosidase is composed of two polypeptide chains. Each chain is made up of 438 amino acids and constitute a subunit of the enzyme. Each of these subunits contains an active site. The active site has three potential components: the pocket, the cleft, and the tunnel. The pocket structure is beneficial for recognition of monosaccharide like glucose. The cleft allows for binding of sugars to form polysaccharides. The tunnel allows for the enzyme to attach to polysaccharide and then release product while still attached to the sugar.Function
The function of the enzyme is to perform hydrolysis of various glycosides and oligosaccharides. The most significant oligosaccharide β-glucosidase reacts with is cellulose. Cellulose is a polymer composed of β-1,4-linked glucosyl residues. β-glucosidases, cellulases, cellobiosidases are required by a number of organisms to consume it. These enzymes are powerful tools for degradation of plant cell walls by pathogens and other organisms consuming plant biomass. β‑glucosidases are essential for many organisms to digest a variety of nutrients. This enzyme completes double-displacement reaction, meaning that the enzyme is changed to an intermediate form when the first substrate enters the active site, it then releases the product before another substrate binds, and reverts to its original form by the end of the reaction. In the case of β-glucosidase, two carboxylate residues of glucosides, cellobiose, cellotriose, cellotetraose are involved at the active site. The purpose of the reaction is to remove the residues from disaccharide cellobiose to produce glucose during the hydrolysis of biomass. Depending on what the enzyme is reacting with the end product will be one or two glucose molecules.Humans
In humans, tissues within the liver, small intestine, spleen and kidney contain a cytosolic β-glucosidase that hydrolyses various β-d-glycosides. This human enzyme shows significant activity towards many xenobiotics commonly found in the human diet including glycosides of phytoestrogens, flavonoids, simple phenolics and cyanogens and human CBG hydrolyses a broad range of dietary glucosides, possibly playing a critical role in xenobiotic metabolism.Liposomal β-glucosidase, found in human lysosomes, plays an important role in the degradation of glycosphingolipids, breaking down glucosylceramide into ceramide and glucose. Gaucher's disease is characterised by an accumulation of glucosylceramide in bodily tissues due to a lack of, or impaired activity of liposomal β-glucosidase, leading to weakened bones, liver damage, and enlargement of the spleen and impairment to its normal function.
Beyond β-glucosidases expressed in human tissues, bacterial β-glucosidases are also found in human saliva and inside the intestine produced by the bacterial microbiota of the mouth and gastro-intestinal tract, with various implications to normal human health, drug and hormone metabolism, and involvement in certain diseases.