Abstract
Antennae-specific odorant-degrading enzymes (ODEs) are postulated to inactivate odorant molecules after they convey their signal. Different classes of insect ODEs are specific to esters, alcohols, and aldehydes – the major functional groups of female-produced, hydrophobic sex pheromones from moth species. Esterases that rapidly inactive acetate and other esters have been well-studied, but less is known about aldehyde oxidases (AOXs). Here we report cloning of an aldehyde oxidase, AtraAOX2, from the antennae of the navel orangeworm (NOW), Amyelois transitella, and the first activity characterization of a recombinant insect AOX. AtraAOX2 gene spans 3,813 bp and encodes a protein with 1,270 amino acid residues. AtraAOX2 cDNA was expressed in baculovirus-infected insect Sf21 cells as a ≈280 kDa homodimer with 140 kDa subunits. Recombinant AtraAOX2 degraded Z11Z13–16Ald and plant volatile aldehydes as substrates. However, as expected for aldehyde oxidases, recombinant AtraAOX2 did not show specificity for Z11Z13–16Ald, the main constituent of the sex pheromone, but showed high activity for plant volatile aldehydes. Our data suggest AtraAOX2 might be involved in degradation of a diversity of aldehydes including sex pheromones, plant-derived semiochemicals, and chemical cues for oviposition sites. Additionally, AtraAOX2 could protect the insect's olfactory system from xenobiotics, including pesticides that might reach the sensillar lymph surrounding the olfactory receptor neurons.
Highlights
In insects, the olfactory system plays an important role in communicating the availability of food sources, habitats, and oviposition sites as well as in locating mates
We performed room temperature (RT)-PCR analysis to determine whether our selected AtraAOXs are expressed in male or female antennae
AtraAOX2 was expressed in antennae of male and female moths, whereas AtraAOX1 was expressed in non-olfactory tissues such as legs, wings, thorax, abdomen, and male and female antennae (Fig. 1)
Summary
The olfactory system plays an important role in communicating the availability of food sources, habitats, and oviposition sites as well as in locating mates. OBPs, including pheromone-binding proteins (PBPs), deliver odorants entering the sensillar lymph to ORs, and at the end of the journey, ODEs play a pivotal role in degrading stray odorants in the peripheral space that could interfere with the fidelity and sensitivity of the insect’s olfactory system [1,2]. During flight male moths need to rapidly inactivate stray odor molecules and reset the olfactory system on a millisecond timescale [3,4]. Their response to sex pheromones can be enhanced or inhibited by plant-derived compounds [5]. Antennae-specific esterases, which degrade sex pheromones with an ester moiety have been well documented in the literature [4,6,7], the role of other ODEs are still poorly understood [2]
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