Amino acid sequence and biological characterization of BlatPLA2, a non-toxic acidic phospholipase A2 from the venom of the arboreal snake Bothriechis lateralis from Costa Rica

Abstract

Bothriechis is considered a monophyletic, basal genus of arboreal Neotropical pitvipers distributed across Middle America. The four species found in Costa Rica (B. lateralis, B. schlegeli, B. nigroviridis, B. supraciliaris) differ in their venom proteomic profiles, suggesting that different Bothriechis taxa have evolved diverse trophic strategies. In this study, we isolated a phospholipase A2 (PLA2) from B. lateralis venom, aiming at increasing our knowledge on the structural and functional characteristics of group II acidic PLA2s, whose toxic actions are generally more restricted than those displayed by basic PLA2s. The new acidic enzyme, BlatPLA2, occurs as a monomer of 13,917 Da, in contrast to many basic group II PLA2s which associate into dimers and often display myotoxicity and/or neurotoxicity. Its amino acid sequence of 122 residues predicts an isoelectric point of 4.7, and displays significant differences with previously characterized acidic PLA2s, with which it shows a maximum sequence identity of 78%. BlatPLA2 is catalytically active but appears to be devoid of major toxic activities, lacking intravenous or intracerebroventricular lethality, myotoxicity, in vitro anticoagulant activity, and platelet aggregation or inhibition effects. Phylogenetic relationships with similar group II enzymes suggest that BlatPLA2 may represent a basal sequence to other acidic PLA2s. Due to the metabolic cost of venom protein synthesis, the presence of a relatively abundant (9%) but non-toxic component is somewhat puzzling. Nevertheless, we hypothesize that BlatPLA2 could have a role in the pre-digestion of prey, possibly having retained characteristics of ancestral PLA2s without evolving towards potent toxicity.