Ussuristatin 2, a Novel KGD-Bearing Disintegrin from Agkistrodon ussuriensis Venom

Two platelet aggregation inhibitors, ussuristatin 1 (US-1) and 2 (US-2), were newly isolated from the venom of Chinese viper (Agkistrodon ussuriensis) by SP-Toyopearl 650M column chromatography and reverse-phase HPLC. The Mrs of these polypeptides were estimated to be about 8,000 by SDS-PAGE. Analytical gel filtration revealed that US-2 exists as a dimer. Both polypeptides comprised 71 amino acids, whose sequences showed high similarities to those of other disintegrins. US-1 had a typical Arg-Gly-Asp (RGD) sequence, which is responsible for blocking the binding of fibrinogen to the receptor. In US-2, the corresponding sequence was Lys-Gly-Asp (KGD). US-1 strongly suppressed platelet aggregation induced by ADP, collagen, thrombin, and epinephrine with IC50 = 17-33 nM. US-2 also inhibited the platelet aggregation, but the IC50s were about ten times higher. US-1 also dose-dependently inhibited the adhesion of human melanoma cells to fibrinogen and fibronectin, while US-2 did not inhibit the cell adhesion to fibronectin. This indicates that the KGD-bearing disintegrin is a specific inhibitor for the fibrinogen receptor.