In N-linked glycoproteins, to which of the following amino acids, oligosaccharides are covalently attached?
Ans: b) Asparagine Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide backbones. Glycoproteins, where N-glycosidic linkage takes place between amide nitrogen of Asparagine, are called as N- linked glycoproteins Types of glycoproteins: 1. N-linked glycoproteins 2. O-linked glycoproteins 3. GPI-anchored proteins O-linked glycoproteins and N-linked glycoproteins are major classes of glycoproteins. O-linked glycoprotein: glycoproteins where O- glycosylation occurs at Serine >> threonine residues N-linked glycoproteins: glycoproteins where N- glycosidic linkage takes place between amide nitrogen of Asparagine. EXTRA EDGE: Periodic acid Schiff (PAS) reagent helps to detect glycoproteins as pink bands after electrophoretic separation. It is a staining method used to detect polysaccharides such as glycogen, and mucosubstances such as glycoproteins, glycolipids, and mucins in tissues. PAS staining can be used to facilitate the diagnosis of several medical conditions: Glycogen storage diseases (versus other storage disorders) Adenocarcinomas, which often secrete neutral mucins Staining of macrophages in Whipple's disease Useful in the diagnosis of A1-antitrypsin deficiency if peripoal liver hepatocytes stain positive.
Glutamine
Asparagine
Acetyl lysine
Serine
Classification of carbohydrate