 Sulfation of heparan sulfate GAGs helps give diversity to cell surface proteins and provides them with a unique sulfation pattern that allows them to specifically interact with other proteins.For example, in mast cells the AT-III-binding pentasaccharaide is synthesized with essential heparan sulfate sulfation steps.The binding of the heparan sulfate in this pentasaccharide to AT-III inactivates the blood-coagulation factors thrombin and Factor Xa.