Oligosaccharide

An oligosaccharide (/ˌɒlɪɡoʊˈsækəˌraɪd/;[1] from Ancient Greek ὀλίγος (olígos) 'few' and σάκχαρ (sákkhar) 'sugar') is a saccharide polymer containing a small number (typically three to ten[2][3][4][5]) of monosaccharides (simple sugars).

N-Linked oligosaccharides are always pentasaccharides attached to asparagine via a beta linkage to the amine nitrogen of the side chain.

[7] Alternately, O-linked oligosaccharides are generally attached to threonine or serine on the alcohol group of the side chain.

In biology, glycosylation is the process by which a carbohydrate is covalently attached to an organic molecule, creating structures such as glycoproteins and glycolipids.

[8] N-Linked glycosylation involves oligosaccharide attachment to asparagine via a beta linkage to the amine nitrogen of the side chain.

Since it is added cotranslationally, it is believed that N-linked glycosylation helps determine the folding of polypeptides due to the hydrophilic nature of sugars.

The asparagine residue linked to an N-linked oligosaccharide usually occurs in the sequence Asn-X-Ser/Thr,[7] where X can be any amino acid except for proline, although it is rare to see Asp, Glu, Leu, or Trp in this position.

[citation needed] Oligosaccharides that participate in O-linked glycosylation are attached to threonine or serine on the hydroxyl group of the side chain.

[7] O-linked glycosylation occurs in the Golgi apparatus, where monosaccharide units are added to a complete polypeptide chain.

[10] Glycosylation sites in O-linked oligosaccharides are determined by the secondary and tertiary structures of the polypeptide, which dictate where glycosyltransferases will add sugars.

[citation needed] Glycoproteins have distinct Oligosaccharide structures which have significant effects on many of their properties,[11] affecting critical functions such as antigenicity, solubility, and resistance to proteases.

There is great diversity in the binding mechanisms of glycolipids, which is what makes them such an important target for pathogens as a site for interaction and entrance.

[citation needed] An important example of oligosaccharide cell recognition is the role of glycolipids in determining blood types.

In response, a reciprocal selectin–oligosaccharide interaction will occur between the two molecules which allows the white blood cell to help eliminate the infection or damage.