ClfA_221-550, a fibrinogen-binding segment of Staphylococcus aureus clumping factor A, disrupts fibrinogen function

Clumping factor A (ClfA) is a surface protein of Staphylococcus aureus bacteria known for its ability to bind the C-terminus of plasma fibrinogen γ chain, which participates in mediating fibrinogen-platelet interaction and fibrin cross-linking, resulting in thrombus formation. With an aim to develop agents that block fibrinogen γ chain C-terminus,the fibrinogen-binding segment of ClfA locating at residues 221-550 was produced by recombinant technology and tested for its ability to inhibit platelet functions and fibrin clot formation. Recombinant ClfA_221-550 bound fibrinogen and blocked fibrinogen-platelet interaction, resulting in the inhibition of both ADP- and collagen-induced platelet aggregations. ClfA_221-550 also affected fibrin clot formation, in which factor XIIIa-mediated cross-linking of fibrinogen γ chains was abrogated by ClfA_221-550 leaving the release of fibrinopeptides A and B from fibrinogen by thrombin unaltered, indicating that ClfA_221-550 interfered with fibrin clot formation without affecting thrombin's catalytic activity. Platelet-mediated clot retraction depends on both platelet-fibrinogen interaction and fibrin clot formation,which makes platelet thrombus less susceptible to fibrinolysis. At the concentration that reduced platelet aggregation by 40%, ClfA_221-550 prevented platelet-mediated clot retraction, whereas the glycoprotein llb\llla antagonist tirofiban needed a higher concentration in inhibiting clot retraction than inhibiting platelet aggregation. By virtue of the multiple effects of ClfA_221-550 on platelet aggregation, fibrin clot formation and platelet-mediated clot retraction,the binding of ClfA_221-550 to fibrinogen merits further investigation for its potential as a new antithrombotic agent.