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

Abstract

Background:β2-Glycoprotein I (β2GPI) 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 β2GPI in thrombus formation is unknown. We have recently shown that β2GPI is susceptible to reduction by the thiol oxidoreductases thioredoxin-1 and protein disulfide isomerase, and that reduction of β2GPI can take place on the platelet surface. Methods:β2GPI, reduced by thioredoxin-1, was labeled with the selective sulfhydryl probe Na-(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 β2GPI 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 β2GPI. Results: We demonstrate that the Cys288–Cys326 disulfide in domain V of β2GPI is the predominant disulfide reduced by thioredoxin-1. Reduced β2GPI in vitro displays increased binding to VWF that is dependent on disulfide bond formation. β2GPI reduced by thioredoxin-1, in comparison with non-reduced β2GPI, 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 β2GPI with VWF may contribute to the redox regulation of platelet adhesion.