Glycoside hydrolase

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Glycoside hydrolases are enzymes that break the bonds between sugar units in complex carbohydrates. They are common in all life and perform many jobs, such as degrading plant materials like cellulose, hemicellulose, and starch; defending against bacteria; helping viruses; and processing sugars inside cells. In bacteria they can act inside the cell or be secreted to help obtain nutrients. In humans they work in the endoplasmic reticulum and Golgi to process glycoproteins and in lysosomes to digest carbohydrates. Defects in specific glycoside hydrolases can cause serious lysosomal storage diseases.

These enzymes are classified as EC 3.2.1 and can also be grouped by how they work: inverting enzymes, which flip the sugar’s configuration, and retaining enzymes, which keep the same configuration after a two-step reaction. They can also be described as endo-acting (cutting in the middle of a chain) or exo-acting (starting from an end). Beyond this, they are grouped by sequence into more than 100 families (the CAZy system) and into larger structural clans. This sequence-based classification helps scientists predict what a given enzyme does and which substrates it acts on.

Many well-known examples include lactase (breaks down lactose), amylase (starch), cellulase (cellulose), xylanase (xylan), lysozyme (bacterial cell walls), neuraminidase (viruses), invertase, hyaluronidase, and chitinase. The CAZy database and its companion CAZypedia provide up-to-date classifications and function predictions for these enzymes.

Glycoside hydrolases are increasingly seen as useful in biorefining: they help convert plant materials into sugars for biofuels, improve food processing (such as producing invert sugar), and support the paper and pulp industry. They are also used in detergents to break down fibers and in organic synthesis to form new glycosides, either by reversing hydrolysis (transglycosylation) or by using engineered forms called glycosynthases and thioglycoligases.

Some glycoside hydrolases help break down microbial biofilms, which can make infections easier to treat when combined with antibiotics. Inhibitors exist, including natural sugar-like molecules and drugs such as acarbose, miglitol, oseltamivir, and zanamivir. Some proteins can also act as glycoside hydrolase inhibitors.