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.

Keywords: Dengue; Enveloped virus; Flaviviridae; Phospholipase A(2); Snake venom; Virucidal.