1INRA-Unité de Phytopharmacie et Médiateurs Chimiques- Bât. A, route de Saint-Cyr, 78026 Versailles Cedex, France.
2University of South Carolina, Department of Biological Sciences, Columbia, SC 29208, USA.
In moths, two classes of odorant-binding proteins were primarily defined, pheromone-binding proteins (PBP) and general odorant-binding proteins (GOBP). If specific binding with pheromonal compounds was clearly demonstrated for the PBPs, no specific ligand has yet been characterized for the GOBPs and authors have suggested that GOBPs could bind general odorants such as host-plant volatiles, with a low selectivity. In Mamestra brassicae, a GOBP2 was purified from antennal extracts and the corresponding cDNA was cloned in an expression vector to produce a recombinant protein. Here we report the binding abilities and expression pattern of MbraGOBP2, in order to relate primary structure and localisation to the function.
In binding experiments, Mbra-GOBP2 only binds the tritiated analogue of Z11-16:OH but not the pheromonal compounds : 3H-16 :Ac, 3H-Z11-16:Ac and 3H-Z11-18:Ac. Although the proper ligands of the GOBPs have still to be characterised, we evidenced the binding selectivity of MbraGOBP2 for the Z11-16:OH. This molecule is the metabolite of esterase degradation of the major pheromonal compound, Z11-16 :Ac in the sensillar lymph. It is also a inhibitor of M. brassicae male courtship behavior. In situ hybridization studies have shown GOBP2 expression in the ventro-lateral region with row pattern consistent with the distribution of long sensilla trichodea. In this kind of sensilla, one olfactory receptor neuron respond to Z11-16:OH. Taken together, those data bring the hypothesis that GOBP2 could be implicated in the detection of heterospecific compounds/inhibitors in male antennae.