Physicochemical Features of Thrombin Binding to Platelet Membrane

Thrombin is a key enzyme of the blood coagulation system, which has been actively studied since the beginning of the last century. The formation of thrombin from prothrombin in the vicinity of vessel injury leads not only to the formation of fibrin—an important structural component of the hemostatic clot—but also to the activation of platelets, endothelium and immune system cells. The binding of thrombin to the platelet surface is thought to play a critical role in the process of platelet activation and may also ensure the maintenance of a high concentration of thrombin within the thrombus due to the concentration of protease on the platelet surface. Nowadays, all major thrombin receptors on platelets have been thoroughly characterized: through various experimental methods, the physicochemical parameters of the corresponding intermolecular interactions have been established. Since the interaction of thrombin with platelets leads to their activation, which includes changes in the number of receptors as a result of granule secretion, the interpretation of the observed kinetic binding curves faces a number of difficulties. It is known that as a result of platelet activation some receptors are able to redistribute on the membrane and form dimers and clusters, which makes the kinetics of thrombin binding to platelets an extremely complex process dependent on many factors, such as activator concentrations, platelet state, and other local parameters of the system. This review aims to describe the current understanding of the interaction of thrombin with the platelet membrane and to outline important unresolved issues in this area of research. The review provides not only information on structural and kinetic features of thrombin binding to individual platelet membrane proteins, but also analyzes the relationship between the relevant interaction parameters and previously obtained data on the integral kinetics of protease binding to the platelet surface.