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.

Naturally occurring free thiols within β2-glycoprotein I in vivo: nitrosylation, redox modification by endothelial cells, and regulation of oxidative stress–induced cell injury

“…44 Although this may seem paradoxical, other proteins such as PDI have also been described as having both procoagulant effects on platelets and protective effects on endothelial cells. 40,45,46 Furthermore, during periods of coagulation, the maintenance of vascular endothelial integrity may be important in supporting crucial chemical and cellular interactions, and reduced ␤2GPI may have a dual role in promoting such mechanisms.…”

Lateral self-association of VWF involves the Cys2431-Cys2453 disulfide/dithiol in the C2 domain

“…␤ 2 -Glycoprotein I reduced with thioredoxin forms disulfide-linked complexes with VWF. 33 This suggests that the Cys288 and/or Cys326 thiols of reduced ␤ 2 -glycoprotein I can attack the Cys2431-Cys2453 (or Cys2451-Cys2468) disulfide of VWF. Similarly, ADAMTS13 contains unpaired cysteine thiols in the C-terminal region that react with the C2 domain of VWF.…”

“…Two candidates are thioredoxin and protein disulfide isomerase (PDI). Thioredoxin has been shown to cleave the Cys288-Cys326 disulfide bond in ␤ 2 -glycoprotein I in plasma, [32][33][34] as well as in 2 other disulfide bonds with the same ϪRHStaple configuration as the VWF Cys2451-Cys2468 bond. 28,29 Conversely, PDI [35][36][37] is on the surface of platelets 38 and platelet microparticles 39 and so will be in the vicinity of VWF during thrombus formation.…”

Thioredoxin and Thioredoxin Reductase Control Tissue Factor Activity by Thiol Redox-dependent Mechanism

“…Within the Trx system, electrons transfer between NADP(H) and Trx via TrxR (18). The reduced form of Trx may reduce a broad range of substrates (19), including the proteins related to coagulation, such as ␤2-glycoprotein 1 (20) and human factor VIII complex (21). Dysfunction of Trx system is related to many disease processes (22).…”