In Vitro Study of the Fibrinolytic Activity via Single Chain Urokinase-Type Plasminogen Activator and Molecular Docking of FGFC1

Fungi fibrinolytic compound 1 (FGFC1) is a rare marine-derived compound that can enhance fibrinolysis both in vitro and in vivo. The fibrinolytic activity characterization of FGFC1 mediated by plasminogen (Glu-/Lys-) and a single-chain urokinase-type plasminogen activator (pro-uPA) was further evaluated. The binding sites and mode of binding between FGFC1 and plasminogen were investigated by means of a combination of in vitro experiments and molecular docking. A 2.2-fold enhancement of fibrinolytic activity was achieved at 0.096 mM FGFC1, whereas the inhibition of fibrinolytic activity occurred when the FGFC1 concentration was above 0.24 mM. The inhibition of fibrinolytic activity of FGFC1 by 6-aminohexanoic acid (EACA) and tranexamic acid (TXA) together with the docking results revealed that the lysine-binding sites (LBSs) play a crucial role in the process of FGFC1 binding to plasminogen. The action mechanism of FGFC1 binding to plasminogen was inferred, and FGFC1 was able to induce plasminogen to exhibit an open conformation by binding through the LBSs. The molecular docking results showed that docking of ligands (EACA, FGFC1) with receptors (KR1-KR5) mainly occurred through hydrophilic and hydrophobic interactions. In addition, the binding affinity values of EACA to KR1-KR5 were -5.2, -4.3, -3.7, -4.5, and -4.3 kcal/moL, respectively, and those of FGFC1 to KR1-KR5 were -7.4, -9.0, -6.3, -8.3, and -6.7 kcal/moL, respectively. The findings demonstrate that both EACA and FGFC1 bound to KR1-KR5 with moderately high affinity. This study could provide a theoretical basis for the clinical pharmacology of FGFC1 and establish a foundation for practical applications of FGFC1.