Functional characterization of a new class of odorant-binding proteins in the moth Mamestra brassicae

A new protocol of binding assay allowed us to functionally characterize two additional odorant-binding proteins in antennae of the moth Mamestra brassicae. These proteins have no N-terminal sequence homology with the moth pheromone-binding proteins and general odorant-binding proteins previously described. One of the two proteins designated MbraAOBP2 is between 60 and 73% similar in N-terminal to several proteins characterized in chemosensory organs of Diptera, Hymenoptera, Lepidoptera, and Phasmids, indicating that these proteins constitute a new group of odorant-binding proteins. A particularly high similarity between MbraAOBP2 and ejaculatory bulb specific protein III of Drosophila suggested that vaccenyl acetate could be a specific ligand for these proteins. As a matter of fact, MbraAOBP2 bound vaccenyl acetate in vitro, but we failed to detect any receptor cell in long and short sensilla trichodea of males. This protocol could be used as a rapid method to identify new odorant-binding proteins in chemosensory organs or tissues.