Effects of Sulfation on Antithrombin-Thrombin/Factor Xa Interactions in Semisynthetic Low-Molecular Weight Heparins

Most of the biological effects of heparin and low molecular weight (LMW) heparins are related to their ability to bind to many different proteins. To gain insight into structure-activity relationships, we investigated quantitatively the interactions of a series of sulfated LMW heparins of similar molecular weights (deriving from statistical desulfation of a supersulfated heparin) with the target-enzymes human antithrombin III (AT) and thrombin (T). In addition, we analyzed the activation process of the protease inhibitor against T and factor Xa (Xa). A non-linear correlation between strength of the AT-heparin complex and the sulfation degree of the LMW heparins was observed, whereas only a modest modulation of T binding to heparin occurred. The efficiency of the heparin derivatives in activating AT towards the proteases is generally high for derivatives exhibiting a low dissociation constant. Only the supersulfated LMW heparin shows a serpine activation ability higher than expected from the affinity studies. These results indicate that chemical modification of sulfation pattern of LMW-heparin can be used to efficiently modulate binding affinity and activity towards biological targets.