Toxinology

Investigations of porcine cerebral cortex neuronal membrane receptors of ammodytoxin have shown that there are two proteins that bind ammodytoxin. The large one R180, a 180 kDa protein, is related to PLA2 receptor from rabbit sceletal muscle and also similar to slightly larger (200 kDa) PLA2 receptor found in porcine liver. Besides neurotoxic PLA2s it binds also non-toxic enzymes. The other, 25 kDa high affinity receptor found to be present in one of the intracelular membranes of porcine cerrebral cortex binds strongly only particular neurotoxic PLA2s. It differs in pharmacological and structural properties from all other PLA2 receptors identified so far. Some residues involved in toxicity of ammodytoxin were identified by site-directed mutagenesis. They are located in the C-terminal region of the molecule. Exchange of Tyr115 and Ile 116 for two Lys resulted in a drastic, two orders of magnitude, drop of lethality, whereas enzymatic activity was decreased only twofold. The two hydrophobic residues are apparently important for the high toxicity of ammodytoxin A. Basic Lys residues at positions 108 and 111 were substituted with two Asn without having an effect on the toxicity. This means that in these positions the basic residues are not required for the toxic effect of ammodytoxin. Evolutionary investigations of retrotransposon BovB-LINE has shown that this transposable element was horizontally transmitted from ancestral Boidae snakes to ancestor of ruminants about 45 million years ago. This was the first discovery of a horizontal transfer of DNA between two so distant vertebrate classes therefore it attracted considerable interest among evolutionary biologists, which resulted in invitations to present our results at several conferences in Europe and in USA.