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.
Glycosylation may play a role in cell-cell adhesion (a mechanism employed by cells of the immune system) as well.
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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