title: Structural glycobiology of heparin dynamics on the exosite 2 of coagulation cascade proteases: Implications for glycosaminoglycans antithrombotic activity.
abstract: fIIa and fXa are two of the main targets of antithrombin, a serine proteases inhibitor that plays a major role in the regulation of blood clotting. The formation of ternary complexes between such molecules and glycosaminoglycans, as heparin, is the main path for inhibiting those enzymes, which may occur through two distinct mechanisms of action. While these serine proteases present distinct susceptibilities to these paths, in which fIIa demands an interaction with heparin, neither the molecular basis of this differential inhibition nor the role of fIIa glycosylation on this process is fully understood. Thus, the present work evaluated through molecular dynamics simulations the effects of glycosylation on fIIa and the consequences of heparin binding to both proteases function and dynamics. Based on the obtained data, fIIa N-linked glycan promoted an increase in the active site pocket size by stabilizing regions that encircle it, while heparin binding was observed to reverse such an effect. Additionally, heparin orientation observed on the surface of fIIa, but not fXa, allows a linear long-chain heparin binding to antithrombin in ternary complexes. Finally, the enzymes catalytic triad organization was disrupted due to a strong glycosaminoglycan binding to the proteases exosite 2. Such data support an atomic-level explanation for the higher inhibition constant of the antithrombin-heparin complex over fIIa than fXa, as well as for the different susceptibilities of those enzymes for antithrombin mechanisms of action.
authors.affiliation: Centro de Biotecnologia, Universidade Federal do Rio Grande do Sul, Av Bento Gonçalves 9500, CP 15005, Porto Alegre 91500-970, RS, Brazil.
authors.forename: Laercio
authors.initials: L
authors.lastname: Pol-Fachin
authors.forename: Hugo
authors.initials: H
authors.lastname: Verli
mesh_terms: D001777:Blood Coagulation; D020134:Catalytic Domain; D015951:Factor Xa / Q000737:chemistry* / Q000378:metabolism; D065427:Factor Xa Inhibitors; D006493:Heparin / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D056004:Molecular Dynamics Simulation; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D065427:Factor Xa Inhibitors; D006493:Heparin; D013917:Thrombin; D015951:Factor Xa
keywords: fXa; glycosylation; hemostasis; molecular dynamics; thrombin