Abstract
Niemann-Pick proteins type C2 (NPC2) are carriers of cholesterol in vertebrates, with a single member in each species. The high sequence conservation between mammals and across vertebrates is related to their common function. In contrast, NPC2 proteins in arthropods have undergone extensive duplication and differentiation, probably under environmental pressure, and are likely to have different functions. Recent studies have suggested that in arthropods these proteins might act as carriers for semiochemicals and other hydrophobic compounds. In this study we focused on the function of a specific NPC2 gene in the moth Helicoverpa armigera (HarmNPC2-1). This protein binds several flavonoids with micromolar dissociation constants. The best ligand was gossypol, present in cotton, one of the main host plants for H. armigera. Western blot revealed the presence of HarmNPC2-1 in different parts of the body, including the antennae, proboscis, and abdomen. In the antennae, in situ hybridization experiments produced strong staining in auxiliary cells at the base of sensilla trichodea, basiconica, coeloconica, and chaetica. Immunocytochemistry confirmed the expression of the protein in sensilla chaetica. Our results support a role of semiochemical carriers for NPC2 proteins in insects and indicate such proteins as new targets for insecticide-free pest population control.
Highlights
Niemann-Pick proteins of class C2 (NPC2) are present in all vertebrates, where they act as carriers for cholesterol and lipids
While in non-insect arthropods NPC2 proteins could act as semiochemical carriers, in the absence of other suitable candidates, we wondered whether in insects these proteins could share the same function with odorant-binding proteins (OBPs) and chemosensory proteins (CSPs)
To support such hypothesis we need to verify that NPC2 proteins (1) are expressed in the lymph of chemosensory structures and (2) bind odorants and pheromones with some degree of specificity and affinity similar to those of OBPs and CSPs
Summary
Niemann-Pick proteins of class C2 (NPC2) are present in all vertebrates, where they act as carriers for cholesterol and lipids. These genes, unlike those of vertebrates, are highly divergent both within and between species (Pelosi et al, 2014, 2017; Vizueta et al, 2016; Zhu et al, 2016), suggesting that such extensive duplication and differentiation may have probably occurred in arthropods under environmental pressure (Pelosi et al, 2014) These facts, together with their binding affinity for small hydrophobic compounds led to the hypothesis that NPC2 proteins could represent a third class of binding proteins for semiochemicals in arthropods (Pelosi et al, 2014).
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