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Glicoprotein

N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins[1].

A glycoprotein is a biomolecule composed of a protein and a carbohydrate (an oligosaccharide). The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. The addition of sugar chains can happen either at asparagine, and is termed N-glycosylation (see on the right), or at hydroxylysine, hydroxyproline, serine, or threonine, and is termed O-glycosylation. Monosaccharides commonly found in eukaryotic glycoproteins include glucose, N-acetylglucosamine, galactose, N-acetylgalactosamine, mannose, fucose, xylose and N-acetylneuraminic acid (also known as sialic acid). The sugar group(s) can assist in protein folding or improve proteins' stability.

Glycoproteins are often used in proteins that are at least in part located in extracellular space (that is, outside the cell).

Examples

One example of glycoproteins found in the body are mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes.

Glycoproteins are important for immune cell recognition, especially in mammals. Examples of glycoproteins in the immune system are:

Other examples of glycoproteins include:

  • components of the zona pellucida, which surrounds the oocyte, and is important for sperm-egg interaction.
  • structural glycoproteins, which occur in connective tissue. These help bind together the fibers, cells, and ground substance of connective tissue. They may also help components of the tissue bind to inorganic substances, such as calcium in bone.

Soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma.

Hormones

Hormones that are glycoproteins include:

See also

References

  1. Ruddock & Molinari (2006) Journal of Cell Science 119, 4373-4380

External links

Template:Glycoproteins

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