www.diseases-diagnosis.com Homepage Diseases Symptoms Diseases Diagnosis Diseases Treatment Diseases Living Care Diseases Prevention Diseases Research
www
Search
March 26, 2016
Table of Contents

1 Introduction
glycosylation

Wikipedia

 

Glycosylation is the enzymatic process that attaches glycans to protein s, lipid s, or other organic molecules . This enzymatic process produces one of the fundamental biopolymers found in cells (along with DNA, RNA, and proteins). 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. The majority of proteins synthesized in the rough ER undergo glycosylation. It is an enzyme-directed site-specific process, as opposed to the non-enzymatic chemical reaction of glycation. Glycosylation is also present in the cytoplasm and nucleus as the O-GlcNAc modification. Five classes of glycans are produced:

  • N -linked glycans attached to a nitrogen of asparagine or arginine side chains;

  • O -linked glycans attached to the hydroxy oxygen of serine, threonine, tyrosine, hydroxylysine, or hydroxyproline side chains, or to oxygens on lipids such as ceramide;

  • phospho-glycans linked through the phosphate of a phospho-serine;

  • C -linked glycans, a rare form of glycosylation where a sugar is added to a carbon on a tryptophan side chain;

  • glypiation, which is the addition of a GPI anchor that links proteins to lipids through glycan linkages.




The carbohydrate 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.




There are various mechanisms for glycosylation, although most share several common features:

  • Glycosylation, unlike glycation, is an enzymatic process;

  • The donor molecule is often an activated nucleotide sugar;

  • The process is site-specific.




N -linked glycosylation

 

N -linked glycosylation is important for the folding of some eukaryotic proteins. The N -linked glycosylation process occurs in eukaryotes and widely in archaea, but very rarely in bacteria.

O -linked glycosylation

O-linked glycosylation is a form of glycosylation occurring in the Golgi apparatus.

Phospho-Serine Glycosylation

Xylose, fucose, mannose, and GlcNAc phospho-serine glycans have been reported in the literature. Fucose and GlcNAc have been found only in Dictyostelium discoideum , mannose in Leishmania mexicana, and xylose in Trypanosoma cruzi.

C-mannosylation

A mannose sugar is added to the first tryptophan residue in the sequence W-X-X-W (W indicates tryptophan, X is any amino acid). Thrombospondins are one of the most commonly modified proteins, however this form of glycosylation appears elsewhere as well. This is an unusual modification because the sugar is linked to a carbon rather than a reactive atom like a nitrogen or oxygen.

GPI Anchors (Glypiation)

A special form of glycosylation is the GPI anchor. This form of glycosylation functions to attach a protein to a hydrophobic lipid anchor, via a glycan chain. (see also prenylation)




  • Glycorandomization

  • Glycation

  • Advanced glycation endproduct

  • Chemical glycosylation

  • Fucosylation





  • Online textbook of glycobiology with chapters about glycosylation

  • GlyProt: In-silico N-glycosylation of proteins on the web

  • NetNGlyc: The NetNglyc server predicts N-Glycosylation sites in human proteins using artificial neural networks that examine the sequence context of Asn-Xaa-Ser/Thr sequons.

  • Supplementary Material of the Book "The Sugar Code"



This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "glycosylation".


Last Modified:   2010-11-30


Search
All informatin on the site is © www.diseases-diagnosis.com 2002-2011. Last revised: January 2, 2011
Are you interested in our site or/and want to use our information? please read how to contact us and our copyrights.
To let us provide you with high quality information, you can help us by making a more or less donation: