Thermodynamic insights on the effects of low-molecular-weight heparins on antithrombin III

Low-molecular-weight heparins (LMWHs) are used in clinical practice as anticoagulants since they enhance the antithrombin III (ATIII) inhibitory action against coagulation enzymes. This work is focused on the effects on ATIII protein induced by the interaction with LMWHs. In particular, the ATIII thermal stability modifications in the presence of Dalteparin, Enoxaparin and Tinzaparin and their fractionated portions were investigated. Furthermore, the effects of standard heparin and of a synthetic pentasaccharide, namely an α-methylated structural analogue of the ATIII-binding sequence (AGA*IAM), were also assessed. Our results highlight the main contributions concurring at the variation of ATIII thermodynamic properties in the presence of LMWHs, indicating that the thermal stability of the protein mainly depends on the effective [AGA*IA]/[protein] ratio regardless the overall chain peculiarities.