Trimucytin, a collagen-like snake venom protein, activates platelets independent of I-domain within alpha2 subunit of alpha2beta1 integrin

A new feasible method for fibrinogen purification based on the affinity of Staphylococcus aureus clumping factor A to fibrinogen

Plasma fibrinogen participates in several physiological and pathological events thus becoming a useful studying material in biomedical research. Here we report a new convenient method for fibrinogen purification based on the affinity of Staphylococcus aureus clumping factor A to fibrinogen. Clumping factor A (ClfA) is a cell wall-anchored surface protein of S. aureus bacteria that binds with a high affinity to the fibrinogen gamma chain C-terminus via a segment encompassing the residues 221-550. This activity of ClfA (ClfA(221-550)) was produced in fusion to the C-terminus of glutathione-S-transferase (GST) with recombinant technology and used as an affinity ligand to capture plasma fibrinogen. GST-ClfA(221-550) fusion protein was immobilized onto the glutathione-conjugated beads packed in a plastic column by its GST part. Then, this affinity column was loaded with citrated and heparinized human plasma. After washing out unbound proteins, column-captured fibrinogen was specifically eluted down with a citrate buffer solution (50mM, pH 5.6). Purified human fibrinogen exhibited the ability to support platelet adhesion and aggregation and formed fibrin clot by thrombin, indicating that ClfA(221-550)-purified human fibrinogen is a functionally active product. We also found that both the rat and mouse fibrinogens could be purified as well as human fibrinogen with this method. By virtue of its simplicity and feasibility, ClfA(221-550)-based method would be very useful to the investigators who need fibrinogen to perform their studies.

Blockade of glycoprotein IIb/IIIa by crotavirin, a member of disintegrins, prevents platelet from activation and aggregation by Staphylococcus aureus bacteria

Interaction with circulating platelets is considered an important virulent mechanism for Staphylococcus aureus (S. aureus) bacteria to induce endocarditis, a severe infectious disease with high incidence of systemic thrombosis. It therefore represents an important target for pharmacological intervention. In this study, we found that the clinical isolate S. aureus 30326 induced activation and aggregation of washed human platelets in a fibrinogen-dependent manner and this platelet reactivity was abrogated by crotavirin, a snake venom-derived glycoprotein (GP) IIb/IIIa antagonist, indicating that crotavirin is able to protect platelets from activation and aggregation by S. aureus 30326. When tested at a concentration that prevented the platelet reactivity of S. aureus 30326, crotavirin also interfered with the binding of bacteria to washed human platelets supplemented with fibrinogen. The fibrinogen-binding activity of S. aureus has been shown to be essential for S. aureus to trigger platelet activation and aggregation. Crotavirin failed to affect the fibrinogen binding of S. aureus 30326 and neither did it bind to this microbe, suggesting that the inhibitory action of crotavirin on the S. aureus 30326-platelet interaction resulted from the occupation of platelet GPIIb/IIIa. Taken together, these results demonstrate an important role for GPIIb/IIIa in mediating the interaction of platelets with S. aureus in the presence of fibrinogen and platelet GPIIb/IIIa thus appears to be a new target for the intervention of S. aureus-platelet interaction.