Thrombin, a multifunctional serine protease, plays a vital role in platelet activation and aggregation, endothelial cell activation and coagulation. What’s more, trombin is also a central effector of hemostasis, and it hydorlyzes fibrinogen into fibrin, activating platelets and other blood-coagulation factors. Because of these advantages, thrombin is also regarded as the effective therapy for serious diseases, including heart attack and stroke. There are three functional domains, such as two positively charged exosites and the active site, which is composed of a catalytic triad of serine, aspartic acid residues and histidine. Among them, the aspartic acid residues can cleave the appropriate peptide bonds in substrates, containing fibrinogen, clitting factors and protein C.
Aptamers are single-stranded nucleic acids produced by SELEX, and can bind protein to their special targets in order to inhibit its function. A majority of aptamers can be separated to realize thrombin with the best studied being Apt15 and Apt27. Apt15 is the first selected thrombin-binding DNA aptamer, which is 15 bases long and binding to exosite 1. However, Apt27 cannot inhibit thrombin-catalyzed clot formation and its process to regulate thrombin is still unknown.
These information are related to the basic substance--aptamers and trombin. However, these two substances play vital roles in the thrombin mediated hydrolysis of peptide substrates. In this research, the trombin substrates are required.