In moths, high temporal sensitivity in perception of sex pheromones and host plant volatiles suggests the existence of mechanisms acting to maintain antennal sensitivity. The antennal enzymes have been long hypothesized to play a central role in the mechanisms, by rapid metabolism of the odorants soon after the fulfillment of the sensillum receptor activation. In the present study, two putative homologous esterases, SexiCXE13 and SlituCXE13, were cloned by RT-PCR and RACE procedures from Spodoptera exigua and Spodoptera litura, respectively. The phylogenetic tree assigned the two genes into the same group with two previously identified male antennal-specific pheromone-degrading enzymes. SexiCXE13 and SlituCXE13 were expressed in High Five cells, and the enzymatic characteristics and substrate specificity were investigated using the purified recombinant enzymes. Both esterases showed high activity to a variety of acetate substrates, including the sex pheromones, their analogs, and some common plant odorants. Our study, for the first time, provides direct biochemical and molecular evidence that the ubiquitously expressed enzyme has the ability to degrade sex pheromones and plant volatiles, and thus this adds new knowledge to the mechanism underlying the sensitivity of moth olfaction.
Keywords: Spodoptera exigua; Spodoptera litura; activité enzymatique; carboxylesterase; carboxylestérase; enzyme activity; enzyme catabolisant les composés odorants; odorant-degrading enzyme.