Activation of crotoxin B by volvatoxin A2

Comparative studies on three rattlesnake toxins

Toxins from the venoms of Crotalus durissus terrificus, Crotalus s. scutulatus and Crotalus viridis concolor were compared using gel filtration, ion-exchange chromatography on DEAE-Sephacel and denaturing and non-denaturing polyacrylamide gel electrophoresis. The three heterodimeric native toxins behaved similarly on each of the separation media, except that the C. d. terrificus toxin displayed a pronounced tendency to dissociate on DEAE-Sephacel, even in the absence of urea. In the presence of 6M urea, subunit dissociation was quantitative for all three toxins. Recombination of purified subunits resulted in toxins which eluted from the gel filtration column in identical fashion to native toxins. Non-denaturing polyacrylamide gel electrophoretic patterns of recombined toxins actually showed greater band resolution than did the native toxins. Six hybrid toxins were generated on polyacrylamide gels from cross-combinations of purified subunits, each with different mobilities than the parental toxins. Mobilities of the hybrid toxins depended principally upon the mobilities of the basic subunits. All three purified native toxins showed comparable LD50's in female mice (0.039-0.061 micrograms/g). The C. d. terrificus acidic X C. s. scutulatus basic hybrid toxin showed toxicity identical to that of the C. s. scutulatus recombined toxin. Phospholipase activity is associated with the basic subunit in all three toxins. Intact toxins show a distinctive lag in phospholipase activity which is not seen with purified basic subunits alone. These results indicate that the principal toxins in these three venoms are homologous.

A study on the interaction of crotapotin with crotoxin phospholipase A2, notexin and other presynaptic neurotoxins

1 Crotapotin, the acidic subunit of crotoxin, greatly potentiated the presynaptic effect of isolated basic phospholipase A (PLA) of crotoxin in both mouse diaphragm and chick biventer cervicis muscles whereas the myotoxic effect was not affected significantly.2 In contrast to crotoxin PLA, the presynaptic effects of notexin and notechis-5, self-active single chain toxins, were antagonized by crotapotin while actions of beta-bungarotoxin were not affected.3 By assaying PLA activity, crotoxin PLA was found to be unstable in physiological salt solution, especially when in contact with muscle, due to massive non-specific binding to and destruction by the muscle.4 The decline of crotoxin PLA was greatly reduced by the presence of crotapotin but not by another acidic protein, volvatoxin A(2), or heparin.5 Notechis-5 was found to be stable even when in the presence of muscles.6 [(3)H]-acetylated crotoxin PLA, which retained about 40% of its original enzyme and presynaptic blocking activities, also bound rapidly to the mouse diaphragm on incubation and this binding was greatly hindered by the simultaneous addition of crotapotin.7 The prevention of binding of crotoxin PLA by crotapotin occurred mostly at those sites where the binding was easily dissociable on washing. No antagonism of binding occurred at the firmly binding site.8 The binding of [(3)H]-acetylated crotapotin was much less than that of crotoxin PLA, and interestingly, the binding was increased by the latter, suggesting that crotapotin may be first bound to the diaphragm together with crotoxin PLA.9 No specific binding at the endplate zone was found either for crotoxin PLA or for crotapotin.10 It is concluded that crotapotin potentiates the presynaptic effect of crotoxin PLA by curtailing its non-specific affinity with muscles, minimizing its dispersal and destruction en route to the nerve terminal, but not by acting as an affinity probe for the nerve terminal.