P-selectin is a key surface adhesion molecule for the interaction of platelets with leukocytes. We have shown previously that the N-terminal domain of S. aureus extracellular fibrinogen-binding protein (Efb) binds to P-selectin and interferes with platelet-leukocyte aggregate formation. Here, we aimed to identify the minimal Efb motif required for binding platelets and to characterise its ability to interfering with the formation of platelet-leukocyte aggregates.

Using a library of synthetic peptides, we mapped the platelet-binding site to a continuous 20 amino acid stretch. The peptide Efb68-87 was able to bind to resting and, to a greater extent, thrombin-stimulated platelets in the absence of fibrinogen. Dot blots, pull-down assays and P-selectin glycoprotein ligand-1 (PSGL-1) competitive binding experiments identified P-selectin as the cellular docking site mediating Efb68-87 platelet binding. Accordingly, Efb68-87 did not bind to other blood cells and captured platelets from human whole blood under low shear stress conditions. Efb68-87 did not affect platelet activation as tested by aggregometry, flow cytometry and immunoblotting, but inhibited the formation of platelet-leukocyte aggregates (PLAs). Efb68-87 also interfered with the platelet-dependent stimulation of neutrophil extracellular traps (NETs) formation in vitro.

We have identified Efb68-87 as a novel selective platelet-binding peptide. Efb68-87 binds directly to P-selectin and inhibits interactions of platelets with leukocytes that lead to PLA and NET formation. As PLAs and NETs play a key role in thromboinflammation, Efb68-87 is an exciting candidate for the development of novel selective inhibitors of the proinflammatory activity of platelets.