Pheromone binding proteins of the moth Mamestra brassicae: Specificity of ligand binding

Abstract

Several isoforms of pheromone-binding proteins (PBP) and general odorant-binding proteins (GOBP) were previously characterized in the antennae of the cabbage armyworm Mamestra brassicae L. (Lepidoptera: Noctuidae). In further investigations, we used two-dimensional electrophoresis and Western-blotting with antibodies raised against the PBPs of the male: this method revealed more proteins with molecular weight and isoelectric points similar to those of OBPs and confirmed the high level of microdiversity suspected for this family of proteins. The binding of the tritiated major pheromone compound, Z11-16:Ac, with male and female antennal extracts and purified PBPs from male antennae was studied. Only the two isoforms Mbra-1 and Mbra-1′ (N-terminus: SKELI) bound the labelled pheromone, whereas no binding was observed with the Mbra-2 (N-terminus: SQEIM). In female antennal extracts, binding was shown between Z11-16:Ac and the proteins Mbra-1 and GOBP2. These results constitute an unambiguous demonstration of the binding specificity of a PBP to a pheromonal ligand, supporting the hypothesis of active participation of PBPs in odor discrimination, as a filter for odorants, prior to the receptor activation.