Dictionary > Glycoprotein


noun, plural: glycoproteins
Any of the conjugated proteins, characterized by having one or more covalently-linked carbohydrate residues
Glycoconjugates are carbohydrates that are covalently linked to another biomolecule via glycosylation and the carbohydrate constituent of the complex is called a glycan. Examples of glycoconjugates are glycoproteins, glycopeptides, peptidoglycans, glycosides, glycolipids, and lipopolysaccharides.
A glycoprotein pertains to any protein covalently attached to a carbohydrate unit through the process of glycosylation. Some of the common carbohydrate constituents of glycoproteins are β-D-glucose, β-D-galactose, β-D-mannose, α-L-fucose, N-acetylglucosamine, N-acetylgalactosamine, N-acetylneuraminic acid, and xylose. The carbohydrate constituent is attached to the protein via the -OH group of serine or threonine (i.e. O-glycosylated) or via the amide NH2 of asparagine (i.e. N-glycosylated).
Some of the examples where glycoproteins are found naturally:

  • collagen
  • mucins
  • transferrin
  • ceruloplasmin
  • immunoglobulins
  • antibodies
  • histocompatibility antigens
  • hormones (e.g. follicle-stimulating hormone, luteinizing hormone, human chorionic gonadotropin, thyroid-stimulating hormone, erythropoietin, alpha-fetoprotein)
  • various enzymes (e.g. patatin, alkaline phosphatase)
  • various proteins involved in cell to cell interactions
  • lectins
  • selectins
  • various protein receptors, especially involved in hormone and drug action
  • calnexin
  • calreticulin
  • certain regulatory proteins for growth and development
  • certain surface protein membranes of platelets, particularly involved in thrombosis

While technically describing conjugates in which the carbohydrate is less than 4 percent by weight, the term is often used generically to include the mucoproteins and proteoglycans. However, differences in the usage of the terms: glycoprotein, proteoglycan, peptidoglycan, and glycopeptide exist, and therefore, prudence in the usage of these terms has to be exercised.
For instance, proteoglycans may be regarded as a subset of glycoproteins since both of them have a protein core. However, there are differences in several aspects. In structure, glycoproteins have carbohydrate chains attached to a polypeptide side chain whereas proteoglycans have glycosaminoglycan chains attached to the polypeptide. Glycoproteins have lower percentage of non-protein content by weight than proteoglycans (which, in turn, have higher, about 50-60%).
See also:

Related term(s):

  • A1-acid glycoprotein
  • Amyloidogenic glycoprotein
  • Env glycoprotein
  • Glycine-rich beta-glycoprotein
  • Glycoprotein hormone-specific n-acetylgalactosamin
  • Glycoprotein-n-acetylgalactosamine 3-beta-galactos
  • Invariant surface glycoprotein 100
  • Mucus glycoprotein sulfotransferase
  • Myelin-associated glycoprotein
  • P-glycoprotein
  • Platelet glycoprotein gpiib-iiia complex
  • Thy 1 glycoprotein
  • Variable surface glycoprotein

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