The Role of Thiols and Disulfides in Platelet Function

Abstract

Disulfide bonds formed in newly synthesized proteins in the endoplasmic reticulum of cells are important for protein structure and stability. Recent research, however, emphasizes a role for thiol–disulfide reactions with disulfide bond rearrangement as a dynamic process in cell and protein function, and in platelet function in particular. Protein disulfide isomerase was found on the platelet surface where it appears to play an important role in the platelet responses of aggregation and secretion, as well as activation of the platelet fibrinogen receptor, the αIIbβ3 integrin. Additionally, sulfhydryl groups in αIIbβ3 have been implicated in the activation of this integrin. Physiologic concentrations of reduced glutathione generate sulfhydryls in αIIbβ3 and potentiate sulfhydryl-dependent reactions in αIIbβ3. Sulfhydryl labeling in αIIbβ3 is inhibited by phenylarsine oxide, a reagent that binds to vicinal thiols. As vicinal thiols are in equilibrium with disulfide bonds, they provide redox-sensitive sites in αIIbβ3 able to respond to external or cytoplasmic reducing equivalents. Furthermore, protein disulfide isomerase and sulfhydryls are now implicated in platelet adhesion by a second platelet integrin, the α2β1 collagen receptor. Most recently, extracellular sulfhydryls in the P2Y12 ADP receptor were found to be required for platelet activation by this receptor. We here provide an overview of this field with a focus on recent developments, and conclude with a working model.