A new short chain RGD-containing disintegrin, accutin, inhibits the commonpathway of human platelet aggregation

A new short-chain disintegrin, accutin, was purified from the Formosan Agki strodon acutus venom by using of gel filtration, ion exchanger and reverse phase HPLC. The homogeneous protein is a 47-residue polypeptide with a mole cular mass of 5241 Da containing an Arg-Gly-Asp sequence and seven cysteiny l residues at positions highly homologous to other disintegrins. Accutin do se-dependently inhibited human platelet aggregation stimulated by ADP, coll agen, thrombin or the thromboxane analogue U46619 in platelet suspension wi th IC50 Values of 66-267 nM. It was also active in inhibiting platelet aggr egation of platelet-rich plasma. However, accutin apparently did not affect the shape change caused by these agonists. Accutin also inhibited fibrinog en-induced aggregation of human elastase-treated platelets in a dose-depend ent manner. Furthermore, accutin dose-dependently inhibited the binding rea ction of fluorescein isothiocyanate (FITC)-conjugated arietin, a member of the disintegrin family, to human platelets. In addition, the binding of FIT C-conjugated accutin to platelets was almost completely blocked by a monocl onal antibody, 7E3, raised against the platelet glycoprotein IIb/IIIa compl ex. On the other hand, accutin as well as other disintegrins, rhodostomin a nd arietin, exhibited an inhibitory effect on 7E3 binding toward platelets and endothelial cells in a dose-dependent manner. It is concluded that accu tin, a new platelet aggregation inhibitor belonging to the short-chain disi ntegrin family, acts specifically on a binding epitope of GPIIb/IIIa overla pping with that of 7E3, leading to the blockade of fibrinogen binding to it s receptor. (C) 1998 Elsevier Science B.V. All rights reserved.