Glycosylation
[3][4] Five classes of glycans are produced: Glycosylation is the process by which a carbohydrate is covalently attached to a target macromolecule, typically proteins and lipids.
Secondly, N-linked glycans mediate a critical quality control check point in glycoprotein folding in the endoplasmic reticulum.
[6] Glycosylation also plays a role in cell-to-cell adhesion (a mechanism employed by cells of the immune system) via sugar-binding proteins called lectins, which recognize specific carbohydrate moieties.
It is the presence or absence of glycosyltransferases which dictates which blood group antigens are presented and hence what antibody specificities are exhibited.
However, it is more likely that diversification is driven by evasion of pathogen infection mechanism (e.g. Helicobacter attachment to terminal saccharide residues) and that diversity within the multicellular organism is then exploited endogenously.
The N-linked glycosylation process occurs in eukaryotes in the lumen of the endoplasmic reticulum and widely in archaea, but very rarely in bacteria.
It has been suggested this rare finding may be linked to the fact that alpha dystroglycan is highly conserved from lower vertebrates to mammals.
It has been established that, in fact, only two thirds are and that there is a clear preference for the second amino acid to be one of the polar ones (Ser, Ala, Gly and Thr) in order for mannosylation to occur.
[14] Numerous studies have shown that this process plays an important role in the secretion of Trombospondin type 1 containing proteins which are retained in the endoplasmic reticulum if they do not undergo C-mannosylation[14] This explains why a type of cytokine receptors, erythropoietin receptor remained in the endoplasmic reticulum if it lacked C-mannosylation sites.
Unlike the biochemical processes, synthetic glycochemistry relies heavily on protecting groups[18] (e.g. the 4,6-O-benzylidene) in order to achieve desired regioselectivity.
[19] New methods have been developed based on solvent participation or the formation of bicyclic sulfonium ions as chiral-auxiliary groups.
It is a spontaneous reaction and a type of post-translational modification of proteins meaning it alters their structure and biological activity.
It is the covalent attachment between the carbonil group of a reducing sugar (mainly glucose and fructose) and the amino acid side chain of the protein.
It has a direct implication in diabetes mellitus type 2 that can lead to many complications such as: cataracts, renal failure, heart damage...[25] And, if they are present at a decreased level, skin elasticity is reduced which is an important symptom of aging.
[26] One of the modulators that intervene in this process is the Fringe, a glycosyltransferase that modifies the O-fucose to activate or deactivate parts of the signalling, acting as a positive or negative regulator, respectively.
For example, therapeutic efficacy of recombinant human interferon gamma, expressed in HEK 293 platform, was improved against drug-resistant ovarian cancer cell lines.
