RESUMO
A new short-chain disintegrin, accutin, was purified from the Formosan Agkistrodon acutus venom by using of gel filtration, ion exchanger and reverse phase HPLC. The homogeneous protein is a 47-residue polypeptide with a molecular mass of 5241 Da containing an Arg-Gly-Asp sequence and seven cysteinyl residues at positions highly homologous to other disintegrins. Accutin dose-dependently inhibited human platelet aggregation stimulated by ADP, collagen, thrombin or the thromboxane analogue U46619 in platelet suspension with IC50 values of 66-267 nM. It was also active in inhibiting platelet aggregation of platelet-rich plasma. However, accutin apparently did not affect the shape change caused by these agonists. Accutin also inhibited fibrinogen-induced aggregation of human elastase-treated platelets in a dose-dependent manner. Furthermore, accutin dose-dependently inhibited the binding reaction of fluorescein isothiocyanate (FITC)-conjugated arietin, a member of the disintegrin family, to human platelets. In addition, the binding of FITC-conjugated accutin to platelets was almost completely blocked by a monoclonal antibody, 7E3, raised against the platelet glycoprotein IIb/IIIa complex. On the other hand, accutin as well as other disintegrins, rhodostomin and arietin, exhibited an inhibitory effect on 7E3 binding toward platelets and endothelial cells in a dose-dependent manner. It is concluded that accutin, a new platelet aggregation inhibitor belonging to the short-chain disintegrin family, acts specifically on a binding epitope of GPIIb/IIIa overlapping with that of 7E3, leading to the blockade of fibrinogen binding to its receptor.
