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Glycomedicine Technology Research Center

What is Glycan?
Easy introduction to glycans.

About glycans

 Recently, various functions of glycans have been elucidated owing to active researches in glycoscience. Especially, important roles of glycans have been discovered in many fields such as cancer (e.g., metastasis, cancer markers), immunity (e.g., immunoreceptor regulation, immunocyte differentiation, antibody drugs), fertilization, development and differentiation (e.g., regenerative medicine), infectious diseases (e.g., influenza, Helicobacter pylori, cholera toxin), biopharmaceuticals, brain, blood types, and so forth. In most of cases, glycans are present on the cell surface and often referred to as the “cloths of cells” indicating cell properties, which bear functions and roles such as signaling and inter-cell communications specific to each cell.Glycans are recognized on secreted proteins in body fluids, and show a wide variety of functions, which include prevention of aggregation or proteolysis of secret proteins such as interferon and erythropoietin, and transport signaling in our body.

Functions and Roles of Glycans

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 Glycans are fundamental biopolymers bearing biological information and referred to as the third biological chains following nucleic acids and proteins. In humans, glycans are composed of about 10 kinds of monosaccharides that form branching molecules. Most glycans do not exist solely but are binding to proteins or lipids and present as glycoconjugates (glycoproteins or glycolipids). In general, glycans are considered to be closely related to secretion, and actually, most glycans are found in the body fluids as secretory proteins or on the cell surface as membrane proteins or glycolipids.
 In animals, plants and yeast, there are 10 kinds of monosaccharides consisting glycans as glycoconjugates (e.g., glycoproteins, glycolipids, proteoglycans): glucose (Glc), galactose (Gal), mannose (Man), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), fucose (Fuc), sialic acid (Sia, NeuAc), xylose (Xyl), glucuronic acid (GlcA), and iduronic acid (IdoA). Moreover, plant glycans are also composed of rhamnose (Rha), arabinose (Ara), galacturonic acid (GalA), and apiose (Api).
 Glycans of glycoproteins are either N-linked oligosaccharides (N-glycans) or O-linked oligosaccharides (O-glycans), and binding to the side chain of aspartic acid (Asn) or serine (Ser)/threonine (Thr), respectively. Proteoglycans consist of a core protein, (GlcA-Gal-Gal-Xyl) attached on the Ser residue of the core protein, and long glycosaminoglycan chains of repeated disaccharides such as heparan sulfate and chondroitin sulfate elongated from the linkage tetrasaccharide.
 Glycolipids include glycosphingolipids, which are glycosides of ceramide, glycoglycerolipids, which are glycolipids with glycans linked to the glycerol moiety such as acylglycerol, and glycosylphosphatidylinositols (GPI), in which glucosamine or mannose is attached to phosphatidylinositol.