Redox control of β2-glycoprotein I-von Willebrand factor interaction by thioredoxin-1

Abstract

Background: β 2 -Glycoprotein I (β 2 GPI) is an abundant plasma protein that is closely linked to blood clotting, as it interacts with various protein and cellular components of the coagulation system. However, the role of β 2 GPI in thrombus formation is unknown. We have recently shown that β 2 GPI is susceptible to reduction by the thiol oxidoreductases thioredoxin-1 and protein disulfide isomerase, and that reduction of β 2 GPI can take place on the platelet surface. Methods: β 2 GPI, reduced by thioredoxin-1, was labeled with the selective sulfhydryl probe N a -(3-maleimidylpropionyl)biocytin and subjected to mass spectrometry to identify the specific cysteines involved in the thiol exchange reaction. Binding assays were used to examine the affinity of reduced β 2 GPI for von Willebrand factor (VWF) and the effect of reduced β2GPI on glycoprotein (GP)Ibα binding to VWF. Platelet adhesion to ristocetin-activated VWF was studied in the presence of reduced β 2 GPI. Results: We demonstrate that the Cys288-Cys326 disulfide in domain V of β 2 GPI is the predominant disulfide reduced by thioredoxin-1. Reduced β 2 GPI in vitro displays increased binding to VWF that is dependent on disulfide bond formation. β 2 GPI reduced by thioredoxin-1, in comparison with non-reduced β 2 GPI, leads to increased binding of GPIbα to VWF and increased platelet adhesion to activated VWF. Conclusions: Given the importance of thiol oxidoreductases in thrombus formation, we provide preliminary evidence that the thiol-dependent interaction of β 2 GPI with VWF may contribute to the redox regulation of platelet adhesion. © 2010 International Society on Thrombosis and Haemostasis.