THE CDNA CLONING AND MOLECULAR CHARACTERIZATION OF A SNAKE-VENOM PLATELET GLYCOPROTEIN IB-BINDING PROTEIN, MAMUSHIGIN, FROM AGKISTRODON HALYS BLOMHOFFII VENOM

The entire cDNA sequences of a never snake venom platelet glycoprotein (GP) Ib-binding protein (BP) composed of an alpha/beta heterodimeric structure, termed mamushigin, from Agkistrodon halys blamhoffii were d etermined, that include the leader peptides (21/23 amino acid residues ) and mature subunits (136/123 amino acid residues). The mature subuni ts of mamushigin are 37.5% identical, and showed a high degree of simi larity (37.7-67.5% identity) with the respective subunits of group W C -type lectins (19). The sequences of the leader peptides of the mamusi gin subunits showed the highest similarity (alpha-73.9/beta-82.6%) wit h those of factor IX/X-BP from Trimeresurus flavoviridis, and the clea vage site residue in both proteins was the same Ala(-1.) The GPIb-bind ing specificity of mamushigin is strongly supported by several lines o f evidence, but mamushigin can directly aggregate normal platelets, si milar to alboaggregin-B (AL-B) (1). This differs from other GPIb-BP's. In mamushigin-treated platelets, serotonin.was not released, and flow cytometric analysis using a monoclonal antibody PAC-1 totally exclude d platelet GPIIb/IIIa activation. Mamushigin enhanced platelet aggrega tion at low-shear stress, and this effect totally disappeared in the p resence of GPIb-receptor blockers specific for von Willebrand factor b inding, but not by GPIIb/IIIa-receptor blockers. At high-shear stress, mamushigin blocked platelet aggregation in a dose-dependent manner, a s seen with other GPIb-BP's. This paper, therefore, describes the cDNA cloning and molecular characterization of mamushigin which has a diff erent effect on platelet aggregation under different shear stress.