Proteolytic signatures of coagulation identified by plasma peptidomics

Background: Coagulation entails sequential proteolytic events in plasma, ultimately leading to fibrin clot formation. Objectives: In this study, we employed a mass spectrometry-based peptidomics approach to characterize the molecular events of coagulation-induced limited proteolysis. Methods: Citrated plasma from healthy donors was in vitro–coagulated by recalcification combined with the addition of tissue factor (TF) in the absence or presence of hirudin. The formation of endogenous peptide products over time was monitored using a mass spectrometry approach with a de novo algorithm for peptide identification. Results: Plasma coagulation resulted in a distinct peptidome enriched with activation peptides of prothrombin and FXIIIA, fibrinopeptides A and B, reactive center loops of protease inhibitors, the bait region of α2-macroglobulin, and additional proteolytic hotspots outside the coagulation system. While thrombin inhibition blocked almost all TF-initiated limited proteolysis, most events were TF concentration–independent, with the exception of prothrombin, fibrinogen, FV, FXIIIA, α2-macroglobulin, protein C inhibitor, complement C3, and plexin domain-containing 2. The order of events of fibrinopeptide A and B formation—prothrombin conversion, FXIIIA activation, and protease inhibitor proteolysis—followed the kinetics of thrombin generation. Conclusion: Plasma peptidomics of coagulation-initiated limited proteolysis captures peptide products derived from pro- and anticoagulant events and proteolytic signatures beyond the classical coagulation system. We envision that this peptidomics strategy enables the assessment of functional aspects of coagulation in bleeding and thrombotic disorders at the molecular level.