Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. Secreted extracellular proteins are often glycosylated.
N-Acetylglucosamine (GlcNAc) is an amide derivative of the monosaccharide glucose. It is a secondary amide between glucosamine and acetic acid. It is significant in several biological systems.
Hexosaminidase is an enzyme involved in the hydrolysis of terminal N-acetyl-D-hexosamine residues in N-acetyl-β-D-hexosaminides.
The enzyme endoglycosidase H is an enzyme with systematic name glycopeptide-D-mannosyl-N4-(N-acetyl-D-glucosaminyl)2-asparagine 1,4-N-acetyl-beta-glucosaminohydrolase. It is a highly specific endoglycosidase which cleaves asparagine-linked mannose rich oligosaccharides, but not highly processed complex oligosaccharides from glycoproteins. It is used for research purposes to deglycosylate glycoproteins and to monitor intracellular protein trafficking through the secretory pathway.
Beta-1,4-galactosyltransferase 2 is an enzyme that in humans is encoded by the B4GALT2 gene.
O-linked glycosylation is the attachment of a sugar molecule to the oxygen atom of serine (Ser) or threonine (Thr) residues in a protein. O-glycosylation is a post-translational modification that occurs after the protein has been synthesised. In eukaryotes, it occurs in the endoplasmic reticulum, Golgi apparatus and occasionally in the cytoplasm; in prokaryotes, it occurs in the cytoplasm. Several different sugars can be added to the serine or threonine, and they affect the protein in different ways by changing protein stability and regulating protein activity. O-glycans, which are the sugars added to the serine or threonine, have numerous functions throughout the body, including trafficking of cells in the immune system, allowing recognition of foreign material, controlling cell metabolism and providing cartilage and tendon flexibility. Because of the many functions they have, changes in O-glycosylation are important in many diseases including cancer, diabetes and Alzheimer's. O-glycosylation occurs in all domains of life, including eukaryotes, archaea and a number of pathogenic bacteria including Burkholderia cenocepacia, Neisseria gonorrhoeae and Acinetobacter baumannii.
Beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:O-glycosyl-glycoprotein 6-beta-N-acetyl-D-glucosaminyltransferase. This enzyme catalyses the following chemical reaction
Alpha-1,6-mannosyl-glycoprotein 2-beta-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:6-(alpha-D-mannosyl)-beta-D-mannosyl-glycoprotein 2-beta-N-acetyl-D-glucosaminyltransferase. This enzyme catalyses the following chemical reaction
Beta-1,4-mannosyl-glycoprotein 4-beta-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:beta-D-mannosyl-glycoprotein 4-beta-N-acetyl-D-glucosaminyltransferase. This enzyme catalyses the following chemical reaction
Acetylgalactosaminyl-O-glycosyl-glycoprotein beta-1,3-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:N-acetyl-beta-D-galactosaminyl-R 3-beta-N-acetyl-D-glucosaminyltransferase. This enzyme catalyses the following chemical reaction
Alpha-1,6-mannosyl-glycoprotein 6-beta-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:6-(2- -alpha-D-mannosyl)-glycoprotein 6-beta-N-acetyl-D-glucosaminyltransferase. This enzyme catalyses the following chemical reaction
Alpha-1,6-mannosyl-glycoprotein 4-beta-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:2,6-bis(N-acetyl-beta-D-glucosaminyl)-alpha-D-mannosyl-glycoprotein 4-beta-N-acetyl-D-glucosaminyltransferase. This enzyme catalyses the following chemical reaction
N-acetyl-beta-glucosaminyl-glycoprotein 4-beta-N-acetylgalactosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-galactosamine:N-acetyl-beta-D-glucosaminyl-group 4-beta-N-acetylgalactosaminyltransferase. This enzyme catalyses the following chemical reaction
Protein O-GlcNAc transferase also known as OGT or O-linked N-acetylglucosaminyltransferase is an enzyme that in humans is encoded by the OGT gene. OGT catalyzes the addition of the O-GlcNAc post-translational modification to proteins.
GDP-Man:Man2GlcNAc2-PP-dolichol alpha-1,6-mannosyltransferase is an enzyme with systematic name GDP-D-mannose:D-Man-alpha-(1->3)-D-Man-beta-(1->4)-D-GlcNAc-beta-(1->4)-D-GlcNAc-diphosphodolichol alpha-6-mannosyltransferase. This enzyme catalyses the following chemical reaction
Dolichyl-P-Man:Man5GlcNAc2-PP-dolichol alpha-1,3-mannosyltransferase is an enzyme with systematic name dolichyl beta-D-mannosyl phosphate:D-Man-alpha-(1->2)-D-Man-alpha-(1->2)-D-Man-alpha-(1->3)-(D-Man-alpha- )-D-Man-beta-(1->4)-D-GlcNAc-beta-(1->4)-D-GlcNAc-diphosphodolichol alpha-1,3-mannosyltransferase. This enzyme catalyses the following chemical reaction
Mannosyl-oligosaccharide 1,2-alpha-mannosidase is an enzyme with systematic name 2-alpha-mannosyl-oligosaccharide alpha-D-mannohydrolase. This enzyme catalyses the following chemical reaction
Mannosyl-oligosaccharide 1,3-1,6-alpha-mannosidase is an enzyme with systematic name (1->3)-(1->6)-mannosyl-oligosaccharide alpha-D-mannohydrolase. This enzyme catalyses the following chemical reaction
Protein O-GlcNAcase (EC 3.2.1.169, OGA, glycoside hydrolase O-GlcNAcase, O-GlcNAcase, BtGH84, O-GlcNAc hydrolase) is an enzyme with systematic name (protein)-3-O-(N-acetyl-D-glucosaminyl)-L-serine/threonine N-acetylglucosaminyl hydrolase. OGA is encoded by the OGA gene. This enzyme catalyses the removal of the O-GlcNAc post-translational modification in the following chemical reaction:
- [protein]-3-O-(N-acetyl-β-D-glucosaminyl)-L-serine + H2O ⇌ [protein]-L-serine + N-acetyl-D-glucosamine
- [protein]-3-O-(N-acetyl-β-D-glucosaminyl)-L-threonine + H2O ⇌ [protein]-L-threonine + N-acetyl-D-glucosamine
O-GlcNAc is a reversible enzymatic post-translational modification that is found on serine and threonine residues of nucleocytoplasmic proteins. The modification is characterized by a β-glycosidic bond between the hydroxyl group of serine or threonine side chains and N-acetylglucosamine (GlcNAc). O-GlcNAc differs from other forms of protein glycosylation: (i) O-GlcNAc is not elongated or modified to form more complex glycan structures, (ii) O-GlcNAc is almost exclusively found on nuclear and cytoplasmic proteins rather than membrane proteins and secretory proteins, and (iii) O-GlcNAc is a highly dynamic modification that turns over more rapidly than the proteins which it modifies. O-GlcNAc is conserved across metazoans.
