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glycoprotein (glīˌkōprōˈtēn), organic compound composed of both a protein and a carbohydrate joined together in covalent chemical linkage. These structures occur in many life forms; they are prevalent and important in mammalian tissues. The attached carbohydrate may have several effects: it may help the protein to fold in the proper geometry, stabilize the protein, affect physical properties such as solubility or viscosity, helps it to orient correctly in a membrane, or make it recognizable to another biochemical or cell (see immunity). Many proteins released by cells to the blood and other fluids are glycoproteins. One set of glycoproteins also carry the blood group determinants. The carbohydrate portion of a glycoprotein is usually a small sugar or no more than 8 to 10 individual monosaccharide units. Combinations of up to seven of the many different sugar molecules known to occur in nature comprise the saccharide portions of mammalian glycoproteins: glucose, glucosamine, galactose, galactosamine, mannose, fucose, and sialic acid (a derivative of glucosamine). The linkage between the oligosaccharide and the protein occurs by formation of a chemical bond to only one of four protein amino acids: asparagine, hydroxylysine, serine, or threonine. Solutions of glycoproteins usually exhibit high viscosity, an observation explaining the highly viscous character of egg white, which is composed largely of the glycoprotein ovalbumin. Salivary mucus contains the glycoprotein called mucin. Among other glycoproteins, one particularly interesting example is isolated from certain antarctic fishes who survive near-freezing water temperatures as a result of freezing-point depression of their blood serum by a globular glycoprotein. This molecule is a remarkably effective freezing point depressant.
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A compound in which carbohydrate (sugar) is covalently linked to protein. The carbohydrate may be in the form of monosaccharides, disaccharides, oligosaccharides, or polysaccharides, and is sometimes referred to as glycan. The sugar may be linked to sulfate or phosphate groups. In different glycoproteins, 100–200 glycan units may be present. Therefore, the carbohydrate content of these compounds varies markedly, from 1% (as in the collagens), to 60% (in certain mucins), to >99% (in glycogen). See Collagen, Glycogen

Glycoproteins are ubiquitous in nature, although they are relatively rare in bacteria. They occur in cells, in both soluble and membrane-bound forms, as well as in the intercellular matrix and in extracellular fluids, and include numerous biologically active macromolecules. A number of glycoproteins are produced industrially by genetic engineering techniques for use as drugs; among them are erythropoietin, interferons, colony stimulating factors, and blood-clotting factors. See Genetic engineering

In most glycoproteins, the carbohydrate is linked to the polypeptide backbone by either N- or O-glycosidic bonds. A different kind of bond is found in glycoproteins that are anchored in cell membranes by a special carbohydrate-containing compound, glycosylphosphatidylinositol, which is attached to the C-terminal amino acid of the protein. A single glycoprotein may contain more than one type of carbohydrate-peptide linkage. N-linked units are typically found in plasma glycoproteins, in ovalbumin, in many enzymes (for example, the ribonucleases), and in immunoglobulins. O-linked units are found in mucins; collagens; and proteoglycans (typical constituents of connective tissues), including chondroitin sulfates, dermatan sulfate, and heparin. See Albumin, Carbohydrate, Enzyme, Immunoglobulin, Monosaccharide, Oligosaccharide, Polysaccharide, Protein

Within any organism, all molecules of a particular protein are identical. In contrast, a variety of structurally distinct carbohydrate units are found not only at different attachment sites of a glycoprotein but even at each single attachment site—a phenomenon known as microheterogeneity. For instance, ovalbumin contains one glycosylated amino acid, but over a dozen different oligosaccharides have been identified at that site, even in a preparation isolated from a single egg of a purebred hen.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


Any of a class of conjugated proteins containing both carbohydrate and protein units. Also known as glycopeptide.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
With the intention of optimize the glycoproteins synthesis process, which was hindered by the limitations from homogeneous glycans obtaining, production of the protein backbone, and linkage between glycan and protein backbone, scientists in Creative Biolabs summarize existing knowledge and technologies to propose enhanced glycoprotein synthesis approaches such as native chemical ligation, bacterial oligosaccharyltransferase, glycoprotein remodeling, and in vivo suppressor tRNA technology.
In contrast, in late EMs, the measured values of these glycoproteins in both heifers and cows were found to be 20-30% lower than those of pregnant animals, and individual differences were obtained at the time EMs were observed.
Approximately 75 percent of the RBC's sialic acid is found in GPA (contains M, N and Ena antigens); and in fact, Band 3 and GPA are the most abundant glycoproteins on the red cell surface.
Glycosylation Patterns in Mutagenized rAb Glycoprotein. We tested the potential validity of using LC-tandem mass spectrometry in the determination process for the similarity of biosimilar products to the reference materials in biosimilar samples with a single mutation in amino acid sequences.
[Sd.sup.a] determinant in Tamm Horsfall Glycoprotein. The Tamm Horsfall Glycoprotein was first recognized as a urinary mucoprotein.
Crivello et al., "Association between platelet glycoprotein Ib-a and myocardial infarction: results of a pilot study performed in male and female patients from Sicily," Annals of the New York Academy of Sciences, vol.
Glycoprotein C is the major BoHV surface protein and is involved in attachment to cellular receptors and interactions with the immune system, acting as a major target for neutralizing antibodies (16,18,23,26), especially the exposed gC N[H.sub.2]-t ectodomain.
Studies using Nipah virus in cats (16,17) and monkeys (18) and HeV in ferrets (15) provided strong evidence that a HeVsG glycoprotein subunit-based vaccine could prevent not only disease but often infection in animals exposed to otherwise lethal doses of Nipah virus or HeV.
Chesterman, "Microheterogeneity of beta-2 glycoprotein I: implications for binding to anionic phospholipids," Biochemical Journal, vol.
A significant (p<0.05) increase of [[alpha].sub.1]-acid glycoprotein concentration in the SCM milk was also observed.
The spawn is held in a substance, glycoprotein, which is stored in the female's body.