Glycoprotein
Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains.
In contrast, perturbation of glycan processing (enzymatic removal/addition of carbohydrate residues to the glycan), which occurs in both the endoplasmic reticulum and Golgi apparatus, is dispensable for isolated cells (as evidenced by survival with glycosides inhibitors) but can lead to human disease (congenital disorders of glycosylation) and can be lethal in animal models.
It is therefore likely that the fine processing of glycans is important for endogenous functionality, such as cell trafficking, but that this is likely to have been secondary to its role in host-pathogen interactions.
[4] Due to the wide array of functions within the body, interest in glycoprotein synthesis for medical use has increased.
[3] An N-linked glycoprotein has glycan bonds to the nitrogen containing an asparagine amino acid within the protein sequence.
[4] An O-linked glycoprotein has the sugar is bonded to an oxygen atom of a serine or threonine amino acid in the protein.
[4] Historically, mass spectrometry has been used to identify the structure of glycoproteins and characterize the carbohydrate chains attached.
[5] One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts.
The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes.
Variable surface glycoproteins allow the sleeping sickness Trypanosoma parasite to escape the immune response of the host.
In addition, as these glycans are much less variable than the underlying protein, they have emerged as promising targets for vaccine design.
[4] For example, P-Glycoprotein causes a decrease in anti-cancer drug accumulation within tumor cells, limiting the effectiveness of chemotherapies used to treat cancer.
Such polysaccharides are also known as glycosaminoglycans.A variety of methods used in detection, purification, and structural analysis of glycoproteins are[8]: 525 [18][10] The glycosylation of proteins has an array of different applications from influencing cell to cell communication to changing the thermal stability and the folding of proteins.
[19] By understanding glycoproteins and their synthesis, they can be made to treat cancer, Crohn's Disease, high cholesterol, and more.
[5] Similarly, an O-linked glycoprotein can be formed through the addition of a glycosyl donor with a protected Serine or Threonine.
[5] Once this linkage is complete, the amino acid sequence can be expanded upon using solid-phase peptide synthesis.
