Dissociation of enzymatic and pharmacological properties of piratoxins-I and -III, two myotoxic phospholipases A(2) from Bothrops pirajai snake venom

Piratoxins (PrTX) I and III are phospholipases A(2) (PLA(2)s) or PLA(2) hom ologue myotoxins isolated from Bothrops pirajai snake venom, which also ind uce myonecrosis, bactericidal activity against Escherichia coli, disruption of artificial membranes, and edema. PrTX-III is a catalytically active hem olytic and anticoagulant Asp49 PLA(2), while PrTX-I is a Lys49 PLA, homolog ue, which is catalytically inactive on artificial substrates, but promotes blockade of neuromuscular transmission. Chemical modifications of His, Lys, Tyr, and Trp residues of PrTX-I and PrTX-III were performed, together with cleavage of the N-terminal octapeptide by CNBr and inhibition by heparin a nd EDTA. The lethality, bactericidal activity, myotoxicity, neuromuscular e ffect, edema inducing effect, catalytic and anticoagulant activities, and t he liposome-disruptive activity of the modified toxins were evaluated. A co mplex pattern of functional differences between the modified and native tox ins was observed. However, in general, chemical modifications that signific antly affected the diverse pharmacological effects of the toxins did not in fluence catalytic or membrane disrupting activities. Analysis of structural changes by circular dichroism spectroscopy demonstrated significant change s in the secondary structure only in the case of N-terminal octapeptide cle avage. These data indicate that PrTX-I and PrTX-III possess regions other t han the catalytic site, which determine their toxic and pharmacological act ivities. (C) 2001 Academic Press.