glycoproteins

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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