1- Definition :
These are heteroproteins resulting from the union of a carbohydrate moiety (de type oligosides) and protein by covalent bonds.
They are widespread in nature and have a wide variety of biological functions. They contain more 5% carbs.
2- The carbohydrate fraction :
We find 4 carbohydrate groups :
- Oses : D- mannose, D- galactose
- 6-désoxyhexoses : L fucose (6 The deoxy -galactose)
- Glucosamine and galactosamine often acetylated.
- Acid acetylneuraminic (NANA) often terminal that gives them acidic glycoproteins.
3- Binding of protein and carbohydrate moieties :
The bond is made between the terminal reducing group of the carbohydrate moiety and an amino acid of the protein at :
- of an alcohol function to an alcohol amino acid (serine, thréonine) = The liaison – glycosidique
- an amide group of glutamine : liaison N-glycosidique
- the connection is made on a specific pattern, in a suitable environment of the protein.
4- biological role of carbohydrate moieties :
- They allow specific recognition by other proteins such as lectins.
- They are involved in cell-cell interaction : contact, information transfer,….
- They influence protein folding.
- They protect the proteins against proteases.
- The specificity of blood grouping depends on the carbohydrate moiety of glycoproteins of red blood cells.
5- The main glycoproteins :
- The pituitary hormones : LH and FSH.
- The plasma glycoprotein : Orosomucoïdes, haptoglobine.
- The glycoproteins egg white : ovalbumine.
- Vegetable glycoproteins and lectins, reagents are used for their properties of agglutination of red blood cells, their mitogenic properties, etc.
During the DR ZEKRI.S – Faculty of Constantine