Extracellular fibrinogen-binding protein, Efb, from Staphylococcus aureus blocks platelet aggregation due to its binding to the α-chain

Extracellular fibrinogen-binding protein (Efb) secreted by Staphylococcus aureus has previously been shown to contribute to pathogenesis in a rat wound infection model. Also antibodies against Efb exhibited a protective effect in a mouse mastitis model. The interaction between Efb and fibrinogen is divalent, with one binding site within the N-terminal repeat region in Efb and one at the C terminus. In this study we show that the distal D domain of fibrinogen contains at least one of the binding domains recognized by Efb. Efb stimulates fibrinogen binding to ADP-activated platelets. Furthermore, Efb inhibits ADP-induced, fibrinogen-dependent platelet aggregation in a concentration-dependent manner. This implies that Efb modifies platelet function by amplifying a non-functional interaction between fibrinogen and platelets. Efb recognizes the A alpha -chain of the D fragment of fibrinogen. The RGD sequence on the A alpha -chain is located close to the region recognized by Efb and contains a putative binding site for the platelet integrin GPIIb/IIIa receptor complex involved in platelet aggregation.