Functional and binding studies of gallic acid showing platelet aggregation inhibitory effect as a thrombin inhibitor

Objective: This study was devoted to identifying natural thrombin inhibitors from traditional Chinese medicine（TCM） and evaluating its biological activity in vitro and binding characteristics.Methods: A combination strategy containing molecular docking, thrombin inhibition assay, surface plasmon resonance（SPR） and molecular dynamics simulation were applied to verify the study result.Results: Gallic acid was confirmed as a direct thrombin inhibitor with IC 50 of 9.07 μmol/L and showed a significant inhibitory effect on thrombin induced platelet aggregation. SPR-based binding studies demonstrated that gallic acid interacted with thrombin with a KDvalue of 8.29 μmol/L. Molecular dynamics and binding free energy analysis revealed that thrombin-gallic acid system attained equilibrium rapidly with very low fluctuations, the calculated binding free energies was-14.61 kcal/mol. Ala230, Glu232, Ser235,Gly258 and Gly260 were the main amino acid residues responsible for thrombin inhibition by gallic acid,providing a mechanistic basis for further optimization.Conclusion: This study proved that gallic acid is a direct thrombin inhibitor with platelet aggregation inhibitory effect, which could provide a basis for the follow-up research and development for novel thrombin inhibitors.