glycoprotein

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glycoprotein

(glī'kōprō`tēn), organic compound composed of both a proteinprotein,
any of the group of highly complex organic compounds found in all living cells and comprising the most abundant class of all biological molecules. Protein comprises approximately 50% of cellular dry weight.
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 and a carbohydratecarbohydrate,
any member of a large class of chemical compounds that includes sugars, starches, cellulose, and related compounds. These compounds are produced naturally by green plants from carbon dioxide and water (see photosynthesis).
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 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 immunityimmunity,
ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
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). Many proteins released by cells to the blood and other fluids are glycoproteins. One set of glycoproteins also carry the blood groupblood groups,
differentiation of blood by type, classified according to immunological (antigenic) properties, which are determined by specific substances on the surface of red blood cells.
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 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: glucoseglucose,
 dextrose,
or grape sugar,
monosaccharide sugar with the empirical formula C6H12O6 . This carbohydrate occurs in the sap of most plants and in the juice of grapes and other fruits.
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, 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: asparagineasparagine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer participates in the biosynthesis of mammalian proteins.
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, hydroxylysine, serineserine
, organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
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, or threoninethreonine
, organic compound, one of the 22 α-amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein.
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. 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.

Glycoprotein

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.

glycoprotein

[¦glī·kō′prō‚tēn]
(biochemistry)
Any of a class of conjugated proteins containing both carbohydrate and protein units. Also known as glycopeptide.
References in periodicals archive ?
Patients were randomized to receive initial open-label enoxaparin or unfractionated heparin therapy followed by edoxaban 60 mg once-daily (dose reduced to 30 mg for CrCL 30 to 50 mL/min, body weight of 60 kg or less, or certain p-glycoprotein inhibitor use) or the comparator, warfarin.
a) Avoid coadministration of P-glycoprotein inducers.
Gefitinib, an EGFR tyrosine kinase inhibitor, directly inhibits the function of P-glycoprotein in multidrug resistant cancer cells.
It has been reported that efflux transport of CoQ10 is mediated by a protein in the membrane of cells called P-glycoprotein (P-gp) in Caco-2 cells.
P-glycoprotein expression in the blood-brain barrier is also affected in patients with brain metastases.
At the end of 12 weeks, the researchers killed half of the animals in order to measure intestinal expression of the membrane efflux transporter P-glycoprotein (PGP), and of the cytochrome P-450 (CYP) metabolism system.
Interestingly, the loss of p-glycoprotein in the knockout mouse resulted in serious Inflammatory Bowel Disease (IBD) IBD is thought to be due to a dysregulated immune response to the toxis produced by the microbiota of the gastrointestinal tract; Past studies have ruled out CD8(+) T cells as the cause of IBD and it is theorized that another subset of T cells, CD4(+) T cells, is responsible for this disease.
independent of P-glycoprotein status and associated with clustering of
0-[infinity]] was obtained due to the interaction between the orange juice and levofloxacin at the intestinal transport system, and it may involve identified mechanisms such as P-glycoprotein or organic anion-transporting polypeptides (OATP) in the gastrointestinal tract in combination with some mild chelation interaction.
The possible pathways for such an interaction are reviewed, including increased stomach absorption, p-glycoprotein activity and interactions in the P450 system.