The
protein disulfide isomerase (PDI) family of
thiol isomerases are intracellular
enzymes known to catalyze the oxidation, reduction and isomerization of
disulfide bonds during
protein synthesis in the endoplasmic reticulum. PDI and related members of the
thiol isomerase family are known to localize extracellularly where they possess various functions. Among these, the role of PDI in the initiation of
thrombus formation is best characterized. PDI is secreted within seconds from activated platelets and endothelial cells at the site of
vascular injury and accumulates in the developing platelet-
fibrin thrombus. Inhibition of PDI by
antibodies or small molecule inhibitors blocks
thrombus formation. Efforts are underway to identify extracellular substrates of PDI that participate in the network pathways linking
thiol isomerases to
thrombus formation. ERp57, ERp5 and
ERp72 also play a role in initiation of
thrombus formation but their specific extracellular substrates are unknown. Areas covered: The following review gives an overview of biochemistry of vascular
thiol isomerases followed by a detailed description of their role in
thrombosis and its clinical implications. Expert commentary: The
thiol isomerase system, by controlling the initiation of
thrombus formation, provides the regulatory switch by which the normal vasculature is protected under physiologic conditions from thrombi generation.