Monday 6 October 2003
Definition: Glycosylation is the process or result of addition of saccharides to proteins and lipids. The process is one of four principal co-translational and post-translational modification steps in the synthesis of membrane and secreted proteins and the majority of proteins synthesized in the rough endoplasmic reticulum (RER) undergo glycosylation. It is an enzyme-directed site-specific process, as opposed to the non-ezymatic chemical reaction of glycation.
There exists N-linked glycosylation (N-glycosylation) to the amide nitrogen of asparagine side chains and O-linked glycosylation (O-glycosylation) to the hydroxy oxygen of serine and threonine side chains.
The polysaccharide chains attached to the target proteins serve various functions. For instance, some proteins do not fold correctly unless they are glycosylated first.
Also, polysaccharides linked at the amide nitrogen of asparagine in the protein confer stability on some secreted glycoproteins. Experiments have shown that glycosylation in this case is not a strict requirement for proper folding, but the unglycosylated protein degrades quickly.
N-linked glycosylation is an essential posttranslational modification of proteins in eukaryotes. The substrate of N-linked glycosylation, dolichol pyrophosphate (DolPP)-GlcNAc(2)Man(9)Glc(3), is assembled through a complex series of ordered reactions requiring the translocation of the intermediate DolPP-GlcNAc(2)Man(5) structure across the endoplasmic-reticulum membrane.
- DNA glycosylases
congenital disorders of glycosylation (CDG syndromes)
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Freeze HH. Congenital Disorders of Glycosylation: CDG-I, CDG-II, and beyond. Curr Mol Med. 2007 Jun;7(4):389-96. PMID: 17584079
Freeze HH.Novel perspectives on glycosylation and human disease. Curr Mol Med. 2007 Jun;7(4):387. PMID: 17584078
Hebert DN, Garman SC, Molinari M. The glycan code of the endoplasmic reticulum: asparagine-linked carbohydrates as protein maturation and quality-control tags. Trends Cell Biol. 2005 Jun 3; PMID: 15939591
Haeuptle MA, Pujol FM, Neupert C, Winchester B, Kastaniotis AJ, Aebi M, Hennet T. Human RFT1 deficiency leads to a disorder of N-linked glycosylation. Am J Hum Genet. 2008 Mar;82(3):600-6. PMID: 18313027