See also ABO blood antigens   See also removing A and B antigens from Type A, B, and AB cells

Glycosidase refers to an enzyme that cleaves a covalent bond between sequential sugars in a glycan or between the sugar and the backbone moiety (e.g., between sugar and peptide backbone of glycoprotein).

Alpha-glucosidase (GAA): breaks down glycogen, a larger molecule, into glucose. 

A person with Pompe’s disease has significantly reduced levels of GAA, or no GAA at all and so is unable to break down glycogen into glucose. That inability results in glycogen accumulating in the muscles of affected patients in excessive amounts. Pompe’s diease is found in two forms -early oset and late onset. Early onset presents shortly after birth. Glycogen accumulates in the pateint’s heart and skeletal uscles, cuasing a progressive deterioration of the heart muscles. Without treatment, a patient with early onset Pompe’s diesase will die form cardiac or respiratory failure before reaching one year of age. 

Following the dsivoery that Pompe’s disease is assocaited with GAA deficiency, researchers tried injecting the enzyme. However, it was taken up by the patient’s liver, reducing glycogen levels there but not in the skeletal or heart uscles where the excess glycogen does the most harm. Later researchers overcame this problem by modifying the injected GAA to include mannose-6-phosphate (M-6P) which promotes GAA uptake in heart and skeletal muscle cells containing M-6-P receptors, including the cells that failed to take up GAA in prior treatment attempts. By 1997, the FDA approved Duke University’s application for Orphan Drug Designation for a new therapy for Pompe’s disease based on the injection of a recombinant form of GAA. See US Patent Nos. 7,351,410 and 7,655,226. 

Plant-derived enzymes

Alpha-galactosidase (E.C. 3.2.1.22); alpha-D-galactoside galactohydrolase): catalyzes the hydrolysis of the terminal linked alpha-galactose moeity from galatose-containing oligosaccarides. These include, for example, the naturally occurring disaccharide melibiose (6-O-alpha-D-galactopyranosyl-D-glucose), the trisaccharide raffinose (O-alpha-D-galactopyranosyl-(1-6)-O-alpha-D-glucopyranosyl-(1-2)-beta-D-f- ructofuranoside) and the tetrasaccharide stachyose (O-alpha-D-galactopyranosyl-(1-6)-O-alpha-D-galactopyranosyl-(1-6)-O-alpha0 a-D-glucopyranosyl-(1-2)-beta-D-fructofuranoside).

Alpha -galactosidases have potential use in various applications. They may hydrolyze alpha-galactose residues form polymeric galactomannans, such as in guar gum which has been used to imporve the gelling properties of the polysaccharide. Alpha-galactosidase can also hydrolyze raffinose from beet sugar syrup, which can be used to facilitate the sugar crystallization from molasses, since the raffinose presents an obstacle to the normal cyrstallization of beet sugar. Alpha-galactosidase can also be used to hydrolyze stachyose and raffinose in soybean milk, thereby reducing or eliminating the undesirable digestive sid eeffects which are associated with soybean milek. The enzyme can also remove the temrinal alpha-galactose residue sfrom other glycans, such as the erythrocyte surface antigen conferring blood group B specificity. This has potential medical use in transfusion therapy by converting blood group type B to unersal donr type O.

Endoglycosidases:

EndoS: The Fc portion of IgG contains a conserved glycan on each heavy chain attached to Asn-297. This oligosaccharide is of the complex biantennary type with a core fucose linked to the innermost N-acetylglucosamine (GlcNAc). These glycans are located in the interface between the CH2 domains (second constant domain of the heavy chains). EndoS is an endoglycosidase secreted by the human pathogenStreptococcus pyogenes. EndoS specifically hydrolyzes the asparagine-linked glycan on IgG between the two core GlcNAc residues. In contrast to many related endoglycosidases that require or are enhanced by denaturation of the glycoprotein substrate, EndoS only hydrolyzes native IgG.

Bjorck (US 2010/0135981) discloses that EndoS is useful in treating diseases such as arthritis and idiopathic thrombocytopenic purpura (ITP) mediated by IgG antibodies by the administration of EndoS polypeptide which hydrolyzes IgG in blood (deglycosylation of IgG). The deglycosylation of IgG by EndoS abrogates its arthritis inducing capacity in mice.

Exoglycosidases

Exoglycosidases modify carbohydrate epitopes on glycoproteins and glycolipids.

Alpha-N-acetylgalactosaminidases (EC 3.2.1.49) are used for destroying A antigens of blood cells.

–N-acetyl-alpha-D-galactosaminidase: from the domestic chicken, Gallus domesticus, is an important exoglycosidase which degrades the human blood group A epitope. The isolated enzyme has a MW of 49.1 kDa and is highly selective for PNP-N-acetyl-alpha-D-galactosaminide. The enzyme hydrozyes the teminal N-acetyl-alpha-D-galactosaminide reisudes form blood group A2 erythroctyes. Protease activity is below detectable limits. The enzyme has a pH optima of 3.7, a pI of 8.15 and is relatively unaffected by ionic strenght and is stable at 4C (Hata, Biochem Int 1992, 28(1): 77-86).

Alpha-galactosidases (EC 3.2.1.22): are used for destroying B antigens of blood cells.

–Alpha-D-Galactosidase: from coffea canephora is an important exoglycosidase which degrades the human blood group B epitope. The isolated enzyme has a MW of 36.7. The isozyme is highly selective for alpha-D-galactosides. It hydrozyles the terminal alpha-D-galactosyl residue from the blood group B epitope. (Haibach, Biochem Biophys Res Commun 1991, 181(3): 1564-71)