Potent virucidal activity against Flaviviridae of a group IIA phospholipase A2 isolated from the venom of Bothrops asper

Abstract

Secreted phospholipase A2 (sPLA2) molecules are small, calcium-dependent enzymes involved in many biological processes. Viperid venoms possess gIIA sPLA2s and sPLA2-like proteins, both having homology to human gIIA sPLA2, an innate immunity enzyme. We evaluated the antiviral action of Mt–I (catalytically-active sPLA2) and Mt-II (catalytically-inactive variant) isolated from the venom of Bothrops asper, against a diverse group of viruses. Yellow Fever and Dengue (enveloped) viruses were highly susceptible to inactivation by the snake proteins, in contrast to Sabin (non-enveloped; Polio vaccine strain), and Influenza A, Herpes simplex 1 and 2, and Vesicular Stomatitis (enveloped) viruses. Titration of the antiviral effect against Dengue virus revealed Mt–I to be highly potent (IC50 0.5–2 ng/mL), whereas Mt-II was 1000-fold weaker. This large difference suggested a requirement for PLA2 activity, which was confirmed by chemical inactivation of Mt–I. A synthetic peptide representing the membrane-disrupting region of Mt-II, previously shown to have bactericidal effect, lacked antiviral action, suggesting that the weak virucidal effect observed for Mt-II is likely caused by contamination with traces of Mt–I. On the other hand, Mt–I was demonstrated to act by a direct virucidal mechanism prior to infection, and not by an independent effect on host cells, either pretreated, or exposed to Mt–I after virus infection. Interestingly, DENV2 propagated in mosquito cells was much more sensitive to the action of Mt–I, compared to human cell-propagated virus. Therefore, differences in envelope membrane composition may be crucially involved in the observed virucidal action of PLA2 enzymes.