title: Extracellular superoxide dismutase in insects: characterization, function, and interspecific variation in parasitoid wasp venom.
abstract: Endoparasitoid wasps inject venom proteins with their eggs to protect them from the host immune response and ensure successful parasitism. Here we report identification of Cu,Zn superoxide dismutase (SOD) transcripts for both intracellular SOD1 and extracellular SOD3 in the venom apparatus of two Leptopilina species, parasitoids of Drosophila. Leptopilina SODs show sequence and structure similarity to human SODs, but phylogenetic analyses indicate that the extracellular SODs are more related to cytoplasmic vertebrate SODs than to extracellular SODs, a feature shared by predicted insect extracellular SODs. We demonstrate that L. boulardi SOD3 is indeed secreted and active as monomeric glycosylated forms in venom. Our results also evidence quantitative variation in SOD3 venom contents between closely related parasitoid species, as sod3 is 100-fold less expressed in Leptopilina heterotoma venom apparatus and no protein and SOD activity are detected in its venom. Leptopilina recombinant SOD3s as well as a mammalian SOD in vitro inhibit the Drosophila phenoloxidase activity in a dose-dependent manner, demonstrating that SODs may interfere with the Drosophila melanization process and, therefore, with production of cytotoxic compounds. Although the recombinant L. boulardi SOD3 quantity needed to observe this effect precludes a systemic effect of the wasp venom SOD3, it is still consistent with a local action at oviposition. This work provides 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.
authors.affiliation: Evolution and Specificity of Multitrophic Interactions, UMR 1301 Biotic Interactions and Plant Health, Institut National de la Recherche Agronomique, INRA PACA, Sophia Antipolis 06903, France. Dominique.Colinet@sophia.inra.fr
authors.forename: Dominique
authors.initials: D
authors.lastname: Colinet
authors.forename: Dominique
authors.initials: D
authors.lastname: Cazes
authors.forename: Maya
authors.initials: M
authors.lastname: Belghazi
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Gatti
authors.forename: Marylène
authors.initials: M
authors.lastname: Poirié
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014862:Wasp Venoms / Q000201:enzymology* / Q000235:genetics; D014863:Wasps / Q000201:enzymology* / Q000235:genetics
chemical_list: D019476:Insect Proteins; D014862:Wasp Venoms; D013482:Superoxide Dismutase