Glycoproteins

Glycoproteins are molecules made from the combination of proteins and carbohydrates.

The Golgi body is the site of most glycoprotein formation which may be either:

• O-linked glycosylation by addition of carbohydrate chains to serine or threonine amino acid residues
• N-linked glycosylation by addition of carbohydrate chains to asparagine residues

Glycoproteins have a number of functions:

• membrane bound:
  • glycocalyx - physical cellular protection
  • immune recognition
  • targetting of membrane-bound vesicles within the cell
  • cell receptors e.g. for LDL and ferritin
  • thyroglobulin, the storage form of thyroxine
  • extracellular matrix recognition molecules e.g. the integrins
    
    
• free:
  • immunoglobulins
  • extracellular matrix components e.g. fibronectin
  • haemoglobin
  • synthetic plasminogen activating factor