β-bungarotoxin

Inhibitory effect of hexapeptide (RGRHGD) on platelet aggregation

The B chain of beta-bungarotoxin 1-6 sequence, RGRHGD, presents the highest local average hydrophilicity measured by Kyte and Doolittle modeling analysis. The RGRHGD holds parts of both RGD and KGD peptides, which have been reported as having high binding affinity to GPIIb-IIIa. The present study evaluates whether the synthesized hexapeptide, RGRHGD, has an antiplatelet effect and further elucidates the possible mechanisms of action. RGRHGD dose-dependently inhibited rabbit platelet aggregation and adenosine triphosphate release induced by arachidonic acid, collagen, platelet-activating factor, thrombin, or U46619 with the IC50 range of 82.7 to 510 microg/mL. The platelet thromboxane B2 formation induced by collagen or thrombin was also significantly decreased by RGRHGD, but there was no effect on arachidonic acid-induced thromboxane B2 formation. In addition, RGRHGD also inhibited the rise of intracellular calcium level stimulated by arachidonic acid, collagen, or thrombin in Fura 2-AM-loaded platelets. The adenosine 3',5'-cyclic monophosphate level of washed platelets was not affected by RGRHGD. In conclusion, these data indicate that the inhibitory effect of RGRHGD on platelet aggregation may be due to the attenuation of thromboxane A2 formation and intracellular calcium mobilization. In addition, this study may provide a useful method of finding potential therapeutic agents by using molecular modeling analysis.

Crystallization and preliminary diffraction data of two myotoxins isolated from the venoms of Bothrops asper (Terciopelo) and Bothrops nummifer (jumping viper)

Two myotoxins isolated from B. asper (myotoxin II) and B. nummifer (myotoxin I) snake venoms have been crystallized and their diffraction properties are described. These myotoxins are phospholipase A2 variants which lack enzymatic activity; B. asper myotoxin II is a lysine-49 phospholipase. Crystals were obtained at room temperature by standard hanging-drop vapour diffusion methods. Crystals diffracted to a resolution of 2.8 and 2.3 A, respectively.

Crystal structure of alpha-dendrotoxin from the green mamba venom and its comparison with the structure of bovine pancreatic trypsin inhibitor

The three-dimensional structure of alpha-dendrotoxin (alpha-DTX) from the green mamba (Dendroaspis angusticeps) venom has been determined crystallographically using the method of isomorphous replacement and refined at 2.2 A resolution using a restrained least-squares method. The crystallographic R-factor is 0.169 for all 3451 measured reflections between 7.0 and 2.2 A. Although the main-chain fold of alpha-DTX is similar to that of homologous bovine pancreatic trypsin inhibitor (BPTI), there are significant differences involving segments of the polypeptide chain close to the "antiprotease site" of BPTI. Comparison of the structure of alpha-DTX with the existing models of BPTI and its complexes with trypsin and kallikrein reveals structural differences that explain the inability of alpha-DTX to inhibit trypsin and chymotrypsin.

Crystallization and preliminary diffraction analysis of caudoxin and notexin; two monomeric phospholipase A2 neurotoxins

Two monomeric neurotoxic phospholipases A2 have been crystallized and their diffraction properties characterized. Crystals of caudoxin (from the venom of Bitis caudalis) and notexin (from the venom of Notechis scutatus scutatus) were grown at neutral pH, in the absence of calcium ion, and diffract to a resolution of 2.3 and 1.6 A, respectively.