Extracellular Fibrinogen-binding Protein (Efb) from Staphylococcus aureus Inhibits the Formation of Platelet-Leukocyte Complexes
Journal of Biological Chemistry
American Society for Biochemistry and Molecular Biology
© 2016 by The American Society for Biochemistry and Molecular Biology, Inc. Open access. Final version free via Creative Commons CC-BY license.
Extracellular fibrinogen-binding protein (Efb) from Staphylococcus aureus inhibits platelet activation, although its mechanism of action has not been established. In this study, we discovered that the N-terminal region of Efb (Efb-N) promotes platelet binding of fibrinogen and that Efb-N binding to platelets proceeds via two independent mechanisms: fibrinogen-mediated and fibrinogen-independent. By proteomic analysis of Efb-interacting proteins within platelets and confirmation by pulldown assays followed by immunoblotting, we identified P-selectin and multimerin-1 as novel Efb interaction partners. The interaction of both P-selectin and multimerin-1 with Efb is independent of fibrinogen. We focused on Efb interaction with P-selectin. Excess of P-selectin extracellular domain significantly impaired Efb binding by activated platelets, suggesting that P-selectin is the main receptor for Efb on the surface of activated platelets. Efb-N interaction with P-selectin inhibited P-selectin binding to its physiological ligand, P-selectin glycoprotein ligand-1 (PSGL-1), both in cell lysates and in cell-free assays. Because of the importance of P-selectin-PSGL-1 binding in the interaction between platelets and leukocytes, we tested human whole blood and found that Efb abolishes the formation of platelet-monocyte and platelet-granulocyte complexes. In summary, we present evidence that in addition to its documented antithrombotic activity, Efb can play an immunoregulatory role via inhibition of P-selectin-PSGL-1-dependent formation of platelet-leukocyte complexes.
This work was possible thanks to grants from Biotechnology and Biological Sciences Research Council (BBSRC) (BB/J002690/1 and BB/J008176/1), Wellcome Trust (ZR-W0258A), British Heart Foundation (PG/15/40/31522), and Royal Society Grant RG120494. T
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Vol. 291 (6), pp. 2764 - 2776