glykosidaasien

Glycosidases, or glycoside hydrolases, are enzymes that catalyze the hydrolysis of glycosidic bonds that join sugar units in carbohydrates and glycoconjugates. By removing sugar residues from substrates such as starch, cellulose, lactose, or glycoproteins, they regulate carbohydrate metabolism, digestion, and remodeling of the extracellular matrix. Glycosidases display broad substrate specificity, with many enzymes acting on a particular linkage type (for example alpha- or beta-glycosidases) rather than a single substrate. Their activity generally results in the production of smaller sugars and/or aglycones.

Mechanism and classification: Glycosidases are categorized into families within the CAZy database as glycoside hydrolases (GHs). They employ two main catalytic strategies: inverting and retaining mechanisms. In inverting enzymes, a single-displacement reaction uses a catalytic acid to donate a proton to the glycosidic oxygen and a general base to activate a water molecule. In retaining enzymes, a two-step double-displacement mechanism uses two conserved carboxylate residues to form a glycosyl-enzyme intermediate and then to regenerate the free enzyme. The specific active-site residues are often aspartate and glutamate. Enzymes may act on mono-, di-, or polysaccharides and are frequently organized into multiple GH families that reflect sequence similarity rather than substrate alone.

Biological and medical relevance: In humans, glycosidases participate in digestion (for example lactase, sucrase–isomaltase), lysosomal degradation of glycoconjugates, and remodeling of extracellular matrices. Deficiencies in particular lysosomal glycosidases cause lysosomal storage diseases, such as Pompe disease (acid alpha-glucosidase), Gaucher disease (glucocerebrosidase), and Fabry disease (alpha-galactosidase A). Industrial and biotechnological applications include processing of dietary sugars, biofuel production from plant polysaccharides, and modification of glycoconjugates in biotechnology.