Sequences, geographic variations and molecular phylogeny of venom phospholipases and threefinger toxins of eastern India Bungarus fasciatus and kinetic analyses of its Pro31 phospholipases A2.

ABSTRACT

Eight phospholipases A2 (PLAs) and four three-finger-toxins (3FTx) from the pooled venom of Bungarus fasciatus (Bf) were previously studied and sequenced, but their expression pattern in individual Bf venom and possible geographic variations remained to be investigated. We herein analyze the individual venom of two Bf specimens from Kolkata (designated as KBf) to address this question. Seven PLAs and five 3FTx were purified from the KBf venoms, and respective cDNAs were cloned from venom glands of one of the snakes. Comparison of their mass and N-terminal sequence revealed that all the PLAs were conserved in both KBf venoms, but that two of their 3FTx isoforms were variable. When comparing the sequences of these KBf-PLAs with those published, only one was found to be identical to that of Bf Vb-2, and the other five were 94-98% identical to those of Bf II, III, Va, VI and XI-2, respectively. Notably, the most abundant PLA isoforms of Bf and KBf venoms contain Pro31 substitution. They were found to have abnormally low k(cat) values but high affinity for Ca2+. Phylogenetic analysis based on the sequences of venom group IA PLAs showed a close relationship between Bungarus and Australian and marine Elapidae. As the five deduced sequences of KBf-3FTx are only 62-82% identical to the corresponding Bf-3FTx from the pooled venom, the 3FTx apparently have higher degree of individual and geographic variations than the PLAs. None of the KBf-3FTx was found to be neurotoxic or very lethal; phylogenetic analyses of the 3FTx also revealed the unique evolution of Bf as compared with other kraits.