A novel pentameric phospholipase A2 myotoxin (PophPLA2) from the venom of the pit viper Porthidium ophryomegas

The first toxin isolated from the venomous pit viper Porthidium ophryomegas is a basic pentameric phospholipase A2 (PophPLA2). Elucidation of its amino acid sequence showed that it belongs to the group IIA of secreted PLA2s, with the presence of all 14 conserved cysteine positions. The toxin displayed catalytic activity, in agreement with the presence of Asp49 in its sequence of 121 residues. SDS-PAGE analysis revealed that this toxin is pentameric in non-reducing conditions, a structural organization that has not been described for any viperid PLA2. PophPLA2 displayed moderate myotoxic (in vivo) and cytotoxic (in vitro) activities, as well as anticoagulant activity on human plasma (in vitro). PophPLA2 was not lethal, and did not induce signs of toxicity or distress in mice, when administered intravenously at a dose of up to 100 μg (5.9 μg/g). The toxin showed highest sequence identity with other PLA2s from the venoms of ancestral Asian pit viper species.