Following identification of intracellular (SOD1) and extracellular (SOD3) Cu,Zn superoxide dismutase transcripts in the venom apparatus of two Leptopilina species, parasitoids of Drosophila, we could demonstrate that L. boulardi SOD3 (LbSOD3) is indeed secreted and active in venom. No SOD protein nor SOD activity were detected in L. heterotoma venom evidencing quantitative interspecific variation. Leptopilina recombinant SOD3s as well as a mammalian SOD in vitro inhibited the Drosophila phenoloxidase activity in a dose-dependent manner, demonstrating that SODs may interfere with the Drosophila melanization process and therefore with production of the host cytotoxic compounds. Phylogenetic analyses of Leptopilina SODs indicated that the extracellular SODs are more related to cytoplasmic vertebrate SODs than to extracellular ones. This work provided the first demonstration that insect extracellular SODs are indeed secreted and active in an insect fluid and can be used as virulence factors to counteract the host immune response, a strategy largely used by bacterial and fungal pathogens but also protozoan parasites during infection.
- Colinet D, Cazes D, Belghazi M, Gatti JL, Poirié M. (2011) Extracellular superoxide dismutase in insects: characterization, function and interspecific variation in parasitoid wasp venom.J. Biol. Chem.286, 40110-40121