Glycosylation

Glycosylation is the reaction in which a carbohydrate (or 'glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not always in chemistry), glycosylation usually refers to an enzyme-catalysed reaction, whereas glycation (also 'non-enzymatic glycation' and 'non-enzymatic glycosylation') may refer to a non-enzymatic reaction.^[1]

Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and functional roles in membrane and secreted proteins.^[2] The majority of proteins synthesized in the rough endoplasmic reticulum undergo glycosylation. Glycosylation is also present in the cytoplasm and nucleus as the O-GlcNAc modification. Aglycosylation is a feature of engineered antibodies to bypass glycosylation.^[3]^[4] Five classes of glycans are produced:

N-linked glycans attached to a nitrogen of asparagine or arginine side-chains. N-linked glycosylation requires participation of a special lipid called dolichol phosphate.
O-linked glycans attached to the hydroxyl oxygen of serine, threonine, tyrosine, hydroxylysine, or hydroxyproline side-chains, or to oxygens on lipids such as ceramide.
Phosphoglycans linked through the phosphate of a phosphoserine.
C-linked glycans, a rare form of glycosylation where a sugar is added to a carbon on a tryptophan side-chain. Aloin is one of the few naturally occurring substances.
Glypiation, which is the addition of a GPI anchor that links proteins to lipids through glycan linkages.

^ Lima, M.; Baynes, J.W. (2013). "Glycation". In Lennarz, William J.; Lane, M. Daniel (eds.). Encyclopedia of Biological Chemistry (Second ed.). Academic Press. pp. 405–411. doi:10.1016/B978-0-12-378630-2.00120-1. ISBN 9780123786319.
^ Varki A, Cummings RD, Esko JD, Freeze HH, Stanley P, Bertozzi CR, Hart GW, Etzler ME (2009). Varki A (ed.). Essentials of Glycobiology (2nd ed.). Cold Spring Harbor Laboratories Press. ISBN 978-0-87969-770-9. PMID 20301239.
^ Jung ST, Kang TH, Kelton W, Georgiou G (December 2011). "Bypassing glycosylation: engineering aglycosylated full-length IgG antibodies for human therapy". Current Opinion in Biotechnology. 22 (6): 858–67. doi:10.1016/j.copbio.2011.03.002. PMID 21420850.
^ "Transgenic plants of Nicotiana tabacum L. express aglycosylated monoclonal antibody with antitumor activity". Biotecnologia Aplicada. 2013.

[1] Lima, M.; Baynes, J.W. (2013). "Glycation". In Lennarz, William J.; Lane, M. Daniel (eds.). Encyclopedia of Biological Chemistry (Second ed.). Academic Press. pp. 405–411. doi:10.1016/B978-0-12-378630-2.00120-1. ISBN 9780123786319.

[varki-2] Varki A, Cummings RD, Esko JD, Freeze HH, Stanley P, Bertozzi CR, Hart GW, Etzler ME (2009). Varki A (ed.). Essentials of Glycobiology (2nd ed.). Cold Spring Harbor Laboratories Press. ISBN 978-0-87969-770-9. PMID 20301239.

[3] Jung ST, Kang TH, Kelton W, Georgiou G (December 2011). "Bypassing glycosylation: engineering aglycosylated full-length IgG antibodies for human therapy". Current Opinion in Biotechnology. 22 (6): 858–67. doi:10.1016/j.copbio.2011.03.002. PMID 21420850.

[4] "Transgenic plants of Nicotiana tabacum L. express aglycosylated monoclonal antibody with antitumor activity". Biotecnologia Aplicada. 2013.

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