1Unité de Phytopharmacie et des Médiateurs Chimiques, INRA, route de Saint-Cyr, 78026 Versailles cedex, France.
2University of South Carolina, Department of Biological Sciences, Columbia, South Carolina 29208, USA.
In insect olfactory system, small soluble proteins highly concentrated in the sensillar lymph of antennal olfactory sensilla are proposed to play an active part in the perireceptor events by transporting the airborne odorant molecules to the olfactory receptor. The antennae of the cabbage armyworm, Mamestra brassicae, express very high levels of such proteins, called OBP for Odorant Binding Proteins. Different binding proteins classes were identified in this species: PBP, GOBP, and a new class refered as to AOBP identified by cross-reactivity with specific antisera and functionnal characterisation, that is binding with pheromone component. N-terminal sequencing revealed that those proteins belong to the a sub-family of proteins whose first member was identified in Drosophila melanogaster and named OS-D. Here we describe the cloning and sequencing of some members of this class of proteins in M. brassicae antennae. Full length cDNA sequences revealed that the gene products contain 128 amino acids including a peptide signal that cleavage results in secreted 112 amino acid mature proteins. The different sequences obtained are very similar to each other and present 4 conserved cystein residues. They present high homologies with proteins of the OS-D class identified in other orders of insects including Diptera, Hymenoptera, Orthoptera, Blattoidea, Phasmatodea. Expression of AOBP analogues was also observed in other organs of M. brassicae adults such as proboscis and tarsi, in which chemosensory neurons are also found. In situ hybridization to RNA was used to study the sites of expression of those proteins and their role is discussed in chemosensory function.