AMINO-ACID-SEQUENCE AND MOLECULAR MODELING OF GLYCOPROTEIN IIB-IIIA AND FIBRONECTIN RECEPTOR ISO-ANTAGONISTS FROM TRIMERESURUS ELEGANS VENOM

Low-molecular-mass Arg-Gly-Asp (RGD)-containing polypeptides were isol ated from the venom of Trimeresurus elegans by a simple two-step proce dure consisting of membrane filtration and reverse-phase HPLC. A combi nation of electrospray MS, fast-atom bombardment MS and Edman degradat ion allowed us to ascertain the presence in the venom of different iso forms and to determine their primary structures. The amino acid sequen ces resembled the structure of elegantin, the only disintegrin previou sly reported from the T. elegans venom [Williams, Rucinski, Holt and N iewiarowski (1990) Biochim. Biophys. Acta 1039, 81-89], MS analyses in dicated the occurrence of differential proteolytic processing at both the N-terminus and the C-terminus of the polypeptide chains. The amino acid sequence alignment of the elegantin isoforms with known componen ts of the disintegrin family demonstrated the complete conservation of the 12 cysteine residues involved in disulphide bridges. Molecular mo delling of elegantins predicted an overall folding of these molecules quite similar to that reported for the kistrin solution structure. The newly identified polypeptide isoforms strongly inhibited ADP-induced aggregation in both human and canine platelet-rich plasma but showed a different species-dependent specificity. These molecules were also ab le to inhibit B16-BL6 murine melanoma cell adhesion to immobilized fib ronectin. The comparison of the structures and biological activities o f elegantin isoforms and kistrin allowed us to highlight some structur al features that, in addition to the RGD locus, might be involved in t he interaction of these snake-venom polypeptides with the integrin rec eptors on the platelet and cell surface.