Allosteric Disulfide Bonds in Thrombosis and Thrombolysis.

Allosteric disulfide bonds control protein function by mediating conformational change when they undergo reduction or oxidation. The known allosteric disulfides are characterized by a particular bond geometry, the -RHStaple. A number of thrombosis and thrombolysis proteins contain one or more disulfide bonds of this type. Tissue factor (TF) is the first haemostasis protein shown to be controlled by an allosteric disulfide, the Cys186-Cys209 bond in the membrane-proximal fibronectin type III domain. TF exists in three forms on the cell surface; a cryptic form that is inert, a coagulant form that binds factor VIIa to initiate coagulation, or a signaling form that binds VIIa and cleaves protease activated receptor 2 that functions in inflammation, tumor progression and angiogenesis. Reduction and oxidation of the Cys186-Cys209 bond is central to the transition between the three activities of TF. The redox state of the bond appears to be controlled by protein disulphide isomerase and NO. Plasmin(ogen), vitronectin, glycoprotein 1balpha, integrin beta3 and thrombomodulin also contain -RHStaple disulfides and there is circumstantial evidence that the function of these proteins may involve redox change of these disulfide bonds.