Functional and expression pattern analysis of chemosensory proteins expressed in antennae and pheromonal gland of Mamestra brassicae

Sequences coding for chemosensory proteins (CSP) CSPMbraA and CSPMbraB, sol uble proteins of low mol. wt, have been amplified using polymerase chain re action on antennal and pheromonal gland complementary DNAs. On the basis of their sequences, these proteins could be classed in the 'OS-D like' protei n family whose first member was described in Drosophila, and that includes proteins characterized in chemosensory organs of many insect phylla, includ ing our recent identification in Mamestra brassicae proboscis. Binding assa ys have shown that these proteins bind the pheromonal component (Z)-11-hexa decenyl-1-acetate (Z11-16:Ac) as well as (Z)-11-octadecenyl-1-acetate (Z11- 18:Ac), an other putative component of the M. brassicae pheromonal blend. F urthermore, binding with fatty acids, but not with progesterone that is a s tructurally unrelated compound, leads to the hypothesis that the odorant-bi nding capability of the MbraCSPs may be restricted to fatty acids and/or to 16-18 carbon backbone skeletons. Thus, these proteins do not show the same highly binding specificity as the pheromone-binding proteins do. The CSP-r elated proteins appear homologous based on sequence identity, conserved cys teine residues and general patterns of expression. However, phylogenetic an alyses suggest the presence of multiple classes of CSP within a given speci es and possible diversification of CSPs within different orders. This diver sity perhaps contributes to the many CSP functions proposed in the literatu re. In M. brassicae, we localized the CSPMbraA expression to the sensilla t richodea, devoted to pheromone reception, suggesting a role in the chemosen sory pathway. However, we also localized such proteins in the pheromonal gl and, devoid of any chemosensory structure. This suggests that the M. brassi cae CSP could be involved in transport of hydrophobic molecules through dif ferent aqueous media, such as the sensillar lymph, as well as the pheromona l gland cytosol.