Protein Glycosylation
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Protein Glycosylation

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There are more than 20 post-translational modification processes in eukaryotic animal cells, such as ubiquitination, phosphorylation, glycosylation, lipidation, methylation and acetylation. Proteins are synthesized by ribosomes translating mRNA into polypeptide chains, which may then undergo PTM consisting in a covalent modification of amino acids. PTMs are particularly important to make the protein obtain more complicated structures, perfect functions, more accurate regulations, and more specific operations.

1. Definition of glycosylation

Protein glycosylation is an enzyme-directed site-specific modification that attaches glycans to proteins in the ER (Endoplasmic Reticulum) and in the Golgi Apparatus body of the cell. Formation of the sugar–amino acid linkage is a significant process in the biosynthesis of the carbohydrate units of glycoproteins. Glycosylation mainly sets into action a complex range of posttranslational enzymatic steps that result in a great diversity of carbohydrate–protein bonds and glycan structures1. Glycans have a variety of critical structural and functional roles in membrane and secreted proteins. Approximately half of all proteins typically synthesized in the rough endoplasmic reticulum undergo glycosylation which can avoid the incorrect folding of the original proteins.

2. Classification of glycosylation

Protein glycosylation can be categorized into four main categories mainly according to various glycosidic linkages between the amino acid and the sugar, including N-linked glycosylation, O-linked glycosylation, C-mannosylation and glycophosphatidlyinositol (GPI) anchor attachments.2

a) N-linked glycans attached to the amide nitrogen of an asparagine (Asn) residue of a protein. Oligosaccharyltransferase (OST) attaches the oligosaccharide chain to asparagine that occurs in the tripeptide sequence, Asn-X-Ser/Thr. X can be any amino acid except for proline.


Fig.1 Structures of N-glycans

b) O-linked glycans attached to the hydroxyl oxygen of serine (Ser), threonine (Thr), tyrosine(Tyr), hydroxylysine(Hyl), or hydroxyproline(Hyp) side-chains, or to oxygens on lipids such as ceramide. O-linked glycosylation is a form of glycosylation that occurs at a later stage in protein processing.


Fig.2 Structures of O-glycans

3. Glycosylation Sites

Glycoprotein analysis requires determining both the sites of glycosylation as well as the glycan structures associated with each site. The presence of the consensus sequence is required for N-linked glycosylation, however the occupation of a potential site is not obligatory. Hence, a glycoprotein may contain a number of potentially N-glycosylated sites, each of which may or may not be glycosylated. Additionally, O-glycosylation may occur at any serine or threonine residue with no single common core structure or consensus protein sequence. While the proteome is coded in the genome, no template exists for glycosylation. Glycans are produced by a set of competing glycosyl transferases. For this reason, the population of glycans occurring at a given site is often not homogeneous; a particular site of N- and O-glycosylation may be occupied by a number of structurally distinct glycans.

4. Biological Function of Glycosylation

  1. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein.3
  2. Glycosylation improves the molecular stability of protein.4
  3. Glycosylation improves the molecular solubility of protein.
  4. Protein glycosylation have an influence on immune function and disease.5

5. O-GlcNAc Glycosylation

O-GlcNAc (termed O-β-GlcNAc or O-Linked β-N-acetylglucosamine) glycosylation, the covalent attachment of β-N-acetylglucosamine to serine or threonine residues of proteins, is an unusual form of protein glycosylation. O-Linked β-N-acetylglucosamine (O-GlcNAc) is both an abundant and dynamic posttranslational modification similar to protein phosphorylation. Notably, alterations in O-GlcNAc glycosyslations is particularly relevant to human pathologies such a diabetes, obesity, cardiovascular disease, neurodegenerative disorders and cancer.


6. Common services of monosaccharide, disaccharide, polysaccharide

Creative peptides recognizes that all our clients have specific and unique requirements. We provide common monosaccharide, disaccharide and polysaccharide services. Other glycosylation modifications (sialic acid, fucose, etc.) can also be performed on the main chain and side chain of the polypeptide. Contact us today for all your needs.


NameCASFormulaAcetate Groups Removed
beta-D-Glucose pentaacetate604-69-3C16H22O11Yes&No
Gluconic acid526-95-4C6H12O7NO
6-phosphogluconic acid921-62-0C6H13O10PNO


NameCASFormulaAcetate Groups Removed
beta-D-Galactose pentaacetate4163-60-4C16H22O11Yes&No


NameCASFormulaAcetate Groups Removed
Fmoc-L-Ser(ManNAc)-OH  Yes&No
Fmoc-Thr(ManNAc)-OH  Yes&No
D-Mannopyranose tetraacetate140147-37-1C14H20O10Yes&No

1. Spiro, R. G. (2002). Protein glycosylation: nature, distribution, enzymatic formation, and disease implications of glycopeptide bonds. Glycobiology, 12(4), 43R.
2. Chen, S. A., Lee, T. Y., & Ou, Y. Y. (2010). Incorporating significant amino acid pairs to identify o-linked glycosylation sites on transmembrane proteins and non-transmembrane proteins. BMC Bioinformatics, 11(1), 536-0.
3. Costa, A. R., Rodrigues, M. E., Henriques, M., Oliveira, Rosário, & Azeredo, J. (2014). Glycosylation: impact, control and improvement during therapeutic protein production. Critical Reviews in Biotechnology, 34(4), 281-299.
4. Ricardo J. Solá, & Griebenow, K. (2009). Effects of glycosylation on the stability of protein pharmaceuticals. Journal of Pharmaceutical Sciences, 98(4), 1223-1245.
5. Wolfert, M. A. & Boons, G. J. (2013). Adaptive immune activation: glycosylation does matter. Nature Chemical Biology, 9(12), 776-784.

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