oligosaccharide
   HOME

TheInfoList



An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a
saccharide is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common ex ...
polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, repeating subunits. Due to their ...

polymer
containing a small number (typically three to ten) of
monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Tab ...
s (simple sugars). Oligosaccharides can have many functions including cell recognition and cell binding. For example,
glycolipid Glycolipids are lipids with a carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consistin ...

glycolipid
s have an important role in the immune response. They are normally present as
glycan The terms glycan and polysaccharide are defined by IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is ...

glycan
s: oligosaccharide chains are linked to
lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
s or to compatible
amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, c ...

amino acid
side chains in
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metabol ...

protein
s, by ''N''- or ''O''-
glycosidic bonds A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. and ethanol Ethanol (also called ethyl alcohol, grain alcohol, dr ...

glycosidic bonds
. ''N''-Linked oligosaccharides are always pentasaccharides attached to
asparagine Asparagine (symbol Asn or N), is an α-amino acid that is Proteinogenic amino acid, used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid gro ...

asparagine
via a beta linkage to the amine nitrogen of the side chain.. Alternately, ''O''-linked oligosaccharides are generally attached to threonine or serine on the alcohol group of the side chain. Not all natural oligosaccharides occur as components of glycoproteins or glycolipids. Some, such as the
raffinose Raffinose is a trisaccharide composed of galactose Galactose (, '' galacto-'' + ''wikt:-ose#Suffix 2, -ose'', "milk sugar") sometimes abbreviated Gal, is a monosaccharide Carbohydrate, sugar that is about as sweetness, sweet as glucose, and ab ...

raffinose
series, occur as storage or transport
carbohydrates is a disaccharide found in animal milk. It consists of a molecule of galactose, D-galactose and a molecule of glucose, D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) an ...
in plants. Others, such as
maltodextrin Maltodextrin is a polysaccharide that is used as a food additive. It is produced from vegetable starch by partial hydrolysis and is usually found as a white hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules vi ...

maltodextrin
s or cellodextrins, result from the microbial breakdown of larger polysaccharides such as starch or cellulose.


Glycosylation

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


''N''-Linked oligosaccharides

''N''-Linked glycosylation involves oligosaccharide attachment to
asparagine Asparagine (symbol Asn or N), is an α-amino acid that is Proteinogenic amino acid, used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid gro ...

asparagine
via a beta linkage to the amine nitrogen of the side chain. The process of ''N''-linked glycosylation occurs cotranslationally, or concurrently while the proteins is being translated. 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. All ''N''-linked oligosaccharides are pentasaccharides: five monosaccharides long. In N-linked glycosylation, ''N''-glycosylation for eukaryotes, the oligosaccharide substrate is assembled right at the membrane of the Endoplasmic reticulum, endoplasmatic reticulum. For prokaryotes, this process occurs at the Cell membrane, plasma membrane. In both cases, the acceptor substrate is an
asparagine Asparagine (symbol Asn or N), is an α-amino acid that is Proteinogenic amino acid, used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid gro ...

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


''O''-Linked oligosaccharides

Oligosaccharides that participate in ''O''-linked glycosylation are attached to threonine or serine on the Hydroxy group, hydroxyl group of the side chain. ''O''-linked glycosylation occurs in the Golgi apparatus, where monosaccharide units are added to a complete polypeptide chain. Cell surface proteins and extracellular proteins are ''O''-glycosylated. Glycosylation sites in ''O''-linked oligosaccharides are determined by the Protein secondary structure, secondary and Protein tertiary structure, tertiary structures of the polypeptide, which dictate where glycosyltransferases will add sugars.


Glycosylated biomolecules

Glycoproteins and glycolipids are by definition Covalent bond, covalently bonded to carbohydrates. They are very abundant on the surface of the cell, and their interactions contribute to the overall stability of the cell.


Glycoproteins

Glycoproteins have distinct Oligosaccharide structures which have significant effects on many of their properties, affecting critical functions such as antigenicity, solubility, and resistance to proteases. Glycoproteins are relevant as Cell surface receptor, cell-surface receptors, cell-adhesion molecules, immunoglobulins, and tumor antigens.


Glycolipids

Glycolipids are important for cell recognition, and are important for modulating the function of membrane proteins that act as receptors. Glycolipids are lipid molecules bound to oligosaccharides, generally present in the lipid bilayer. Additionally, they can serve as receptors for cellular recognition and cell signaling. The head of the oligosaccharide serves as a binding partner in receptor (biochemistry), receptor activity. The binding mechanisms of receptors to the oligosaccharides depends on the composition of the oligosaccharides that are exposed or presented above the surface of the membrane. 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. For example, the chaperone (protein), chaperone activity of glycolipids has been studied for its relevance to HIV infection.


Functions


Cell recognition

All cells are coated in either glycoproteins or glycolipids, both of which help determine cell types. Lectins, or proteins that bind carbohydrates, can recognize specific oligosaccharides and provide useful information for cell recognition based on oligosaccharide binding. An important example of oligosaccharide cell recognition is the role of glycolipids in determining blood types. The various blood types are distinguished by the glycan modification present on the surface of blood cells. These can be visualized using mass spectrometry. The oligosaccharides found on the A, B, and H antigen occur on the Non-reducing sugar, non-reducing ends of the oligosaccharide. The H antigen (which indicates an O blood type) serves as a precursor for the A and B antigen. Therefore, a person with A blood type will have the A antigen and H antigen present on the glycolipids of the red blood cell plasma membrane. A person with B blood type will have the B and H antigen present. A person with AB blood type will have A, B, and H antigens present. And finally, a person with O blood type will only have the H antigen present. This means all blood types have the H antigen, which explains why the O blood type is known as the "universal donor". How do transport vesicles know the final destination of the protein that they are transporting? Vesicles are directed by many ways, but the two main ways are: # The sorting signals encoded in the amino acid sequence of the proteins. # The Oligosaccharide attached to the protein. The sorting signals are recognised by specific receptors that reside in the membranes or surface coats of budding vesicles, ensuring that the protein is transported to the appropriate destination.


Cell adhesion

Many cells produce specific carbohydrate-binding proteins known as lectins, which mediate cell adhesion with oligosaccharides. Selectins, a family of lectins, mediate certain cell–cell adhesion processes, including those of leukocytes to endothelial cells. In an immune response, endothelial cells can express certain selectins transiently in response to damage or injury to the cells. 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. Protein-Carbohydrate bonding is often mediated by hydrogen bonding and van der Waals forces.


Dietary oligosaccharides

Fructooligosaccharide, Fructo-oligosaccharides (FOS), which are found in many vegetables, are short chains of fructose molecules. They differ from fructans such as inulin, which as polysaccharides have a much higher degree of polymerization than FOS and other Oligiosaccharides, but like inulin and other fructans, they are considered soluble dietary fibre. Galactooligosaccharides (GOS), which also occur naturally, consist of short chains of galactose molecules. Breast milk, Human milk is an example of this and contains oligosaccharides, known as human milk oligosaccharides (HMOs), which are derived from lactose. These oligosaccharides have Biology, biological function in the development of the gut flora of infants. Examples include lacto-N-tetraose, lacto-N-neotetraose, and lacto-N-fucopentaose. These compounds cannot be Digestion, digested in the human small intestine, and instead pass through to the large intestine, where they promote the growth of ''Bifidobacterium, Bifidobacteria'', which are beneficial to gut health. Mannan Oligosaccharide based nutritional supplements (MOS), Mannan oligosaccharides (MOS) are widely used in compound feed, animal feed to improve gastrointestinal health. They are normally obtained from the yeast cell walls of ''Saccharomyces cerevisiae''. Mannan oligosaccharides differ from other oligosaccharides in that they are not fermentable and their primary mode of actions include agglutination of type-1 fimbria pathogens and immunomodulation


Sources

Oligosaccharides are a component of Dietary fiber, fibre from plant tissue. FOS and inulin are present in Jerusalem artichoke, burdock, chicory, Leek (vegetable), leeks, onions, and asparagus. Inulin is a significant part of the daily diet of most of the world’s population. FOS can also be synthesized by enzymes of the fungus ''Aspergillus niger'' acting on sucrose. GOS is naturally found in soybeans and can be synthesized from lactose. FOS, GOS, and inulin are also sold as nutritional supplements.


See also

* Carbohydrate synthesis, Oligosaccharide synthesis * Oligosaccharide nomenclature * Isomaltooligosaccharide (IMO)


References


External links

* {{Authority control Oligosaccharides, Nutrition Sugar substitutes Carbohydrate chemistry