Glycosylation


Glycosylation

Glycosylation (see also chemical glycosylation) is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor). In biology glycosylation refers to the enzymatic process that attaches glycans to proteins, lipids, 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.[1] 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:

Contents

Purpose

The carbohydrate chains attached to the target proteins serve various functions.[2] For instance, some proteins do not fold correctly unless they are glycosylated first.[1] 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.

Mechanisms

There are various mechanisms for glycosylation, although most share several common features:[1]

  • Glycosylation, unlike glycation, is an enzymatic process
  • The donor molecule is often an activated nucleotide sugar
  • The process is site-specific.

Types of glycosylation

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.[3]

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. Mannose has recently been reported in a vertebrate, the mouse, Mus musculus, on the cell-surface laminin receptor alpha dystroglycan4. It has been suggested this rare finding may be linked to the fact that alpha dystroglycan is highly conserved from lower vertebrates to mammals.[4]

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 C-modified proteins, although this form of glycosylation appears elsewhere as well. C-mannosylation is unusual because the sugar is linked to a carbon rather than a reactive atom such as nitrogen or oxygen. Recently, the first crystal structure of a protein containing this type of glycosylation has been determined - that of human complement component 8, PDB ID 3OJY.

Formation of GPI anchors (glypiation)

A special form of glycosylation is the formation of a GPI anchor. In this kind of glycosylation a protein is attached to a lipid anchor, via a glycan chain. (See also prenylation.)

See also

References

  1. ^ a b c edited by Ajit Varki ... (2009). Essentials of Glycobiology. Ajit Varki (ed.) (2nd ed.). Cold Spring Harbor Laboratories Press. ISBN 978-087969770-9. 
  2. ^ Drickamer, K; M.E. Taylor (2006). Introduction to Glycobiology (2nd ed.). Oxford University Press, USA. ISBN 978-0199282784. 
  3. ^ William G. Flynne (2008). Biotechnology and Bioengineering. Nova Publishers. pp. 45–. ISBN 9781604560671. http://books.google.com/books?id=WEBBP5IYqJQC&pg=PA45. Retrieved 13 November 2010. 
  4. ^ Yoshida-Moriguchi, T., et al (2010). Science. 327(5961):88-92.

External links


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Glycosylation — C est une réaction enzymatique consistant à lier de façon covalente un glucide à une chaîne peptidique ou une protéine. À ne pas confondre avec la glycation, réaction purement chimique et spontanée. Le processus de glycosylation débute dans le… …   Wikipédia en Français

  • glycosylation — noun Date: 1945 the process of adding glycosyl radicals to a protein to form a glycoprotein • glycosylate transitive verb …   New Collegiate Dictionary

  • glycosylation — The process of adding sugar units such as in the addition of glycan chains to proteins …   Dictionary of molecular biology

  • glycosylation — noun The reaction of a saccharide with a hydroxy or amino functional group to form a glycoside; especially the reaction with a protein or lipid to form a glycoprotein or glycolipid …   Wiktionary

  • glycosylation — Formation of linkages with glycosyl groups, as between d glucose and the hemoglobin chain to form the fraction hemoglobin AIc, whose level rises in association with the raised blood d glucose …   Medical dictionary

  • glycosylation — gly·co·syl·a·tion …   English syllables

  • glycosylation — The covalent addition of sugar or sugar related molecules to other classes of molecule, including proteins or nucleic acids …   Glossary of Biotechnology

  • glycosylation — …   Useful english dictionary

  • Congenital disorder of glycosylation — Congenital disorders of glycosylation Classification and external resources ICD 10 E77.8 ICD 9 271.8 …   Wikipedia

  • O-linked glycosylation — is a form of glycosylation occurring in the Golgi apparatus.[1] Contents 1 O N acetylgalactosamine (O GalNAc) 2 O fucose 3 O glucose …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.