title: Extracellular Fibrinogen-binding Protein (Efb) from Staphylococcus aureus Inhibits the Formation of Platelet-Leukocyte Complexes.
abstract: 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.
authors.affiliation: From the Departments of Biology and Biochemistry and.
authors.forename: Mareike G
authors.initials: MG
authors.lastname: Posner
authors.affiliation: From the Departments of Biology and Biochemistry and.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Upadhyay
authors.affiliation: Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom and.
authors.forename: Aisha Alsheikh
authors.initials: AA
authors.lastname: Abubaker
authors.affiliation: Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom and.
authors.forename: Tiago M
authors.initials: TM
authors.lastname: Fortunato
authors.affiliation: Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom and.
authors.forename: Dina
authors.initials: D
authors.lastname: Vara
authors.affiliation: the Department of Biology and Biotechnology, University of Pavia, 27100 Pavia PV, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Canobbio
authors.affiliation: From the Departments of Biology and Biochemistry and bsssb@bath.ac.uk.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bagby
authors.affiliation: Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom and.
authors.forename: Giordano
authors.initials: G
authors.lastname: Pula
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001792:Blood Platelets / Q000378:metabolism* / Q000473:pathology; D001798:Blood Proteins / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism* / Q000473:pathology; D019007:P-Selectin / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001798:Blood Proteins; C114014:Efb protein, Staphylococcus aureus; D008562:Membrane Glycoproteins; D019007:P-Selectin; C084882:P-selectin ligand protein; C069282:multimerin
keywords: P-selectin; PSGL-1; Staphylococcus aureus (S. aureus); bacterial pathogenesis; fibrinogen; monocyte; neutrophil; platelet; protein-protein interactions; proteomics