Structure of an antennally-expressed carboxylesterase suggests lepidopteran odorant degrading enzymes are broadly tuned

Authors: Corcoran, Jacob; HAMIAUX, CYRIL - New Zealand Institute Of Plant & Food Research; FARAONE, NICOLETTA - Acadia University; LÖFSTEDT, CHRISTER - Lund University; CARRAHER, COLM - New Zealand Institute Of Plant & Food Research

Submitted to: Current Research in Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2023
Publication Date: 6/5/2023
Citation: Corcoran, J., Hamiaux, C., Faraone, N., Löfstedt, C., Carraher, C. 2023. Structure of an antennally-expressed carboxylesterase suggests lepidopteran odorant degrading enzymes are broadly tuned. Current Research in Insect Science. 3. Article 100062. https://doi.org/10.1016/j.cris.2023.100062.
DOI: https://doi.org/10.1016/j.cris.2023.100062

Interpretive Summary: As insects navigate the environment they are inundated with thousands of volatile odorant compounds that are constantly being emitted by microorganisms, plants and other animals. While the vast majority of these compounds carry no “message” that is of interest to a given insect, others carry information that is of critical importance to its survival. In this case, the insect has evolved to depend on these biologically relevant messages to locate mates, find food, or lay eggs, in real time. For this to occur, insects rely on an extraordinarily sensitive and highly efficient odorant processing system comprised of olfactory proteins, each with a distinct role in filtering critical odorant messengers out from a huge collection of environmental noise. One class of these proteins, the odorant degrading enzymes, are widely touted as being ideal targets for the development of next-generation insecticides due to their critical role in maintaining the functionality of the insect olfactory system. In this study we have identified, functionally characterized, and experimentally determined the 3D-structure of an odorant degrading enzyme from the horticultural pest moth, Epiphyas postvittana, which is responsible for significant agricultural losses in the U.S. and abroad. These data represent the first proven structure of an odorant degrading enzyme from a lepidopteran insect, which provides insight into the basic biological characteristics of these olfactory proteins and serves as a basis for the development of novel, olfactory protein-based insecticide development programs.

Technical Abstract: Insects rely on the detection of chemical cues present in the environment to guide their foraging and reproductive behaviour. As such, insects have evolved a sophisticated chemical processing system in their antennae comprised of several types of olfactory proteins. Of these proteins, odorant degrading enzymes are responsible for metabolising the chemical cues within the antennae, thereby maintaining olfactory system function. Members of the carboxyl/cholinesterase gene family are known to degrade odorant molecules with acetate-ester moieties that function as host recognition cues or sex pheromones, however, their specificity for these compounds remains unclear. Here, we evaluate expression levels of this gene family in the light-brown apple moth, Epiphyas postvittana, via RNAseq and identify putative odorant degrading enzymes. We then solve the apo-structure for EposCCE24 by X-ray crystallography to a resolution of 2.43 Å and infer substrate specificity based on structural characteristics of the enzyme’s binding pocket. The specificity of EposCCE24 was validated by testing its ability to degrade biologically relevant and non-relevant sex pheromone components and plant volatiles using GC-MS. We found that EposCCE24 is neither capable of discriminating between linear acetate-ester odorant molecules of varying chain length, nor between molecules with varying double bond positions. EposCCE24 efficiently degraded both plant volatiles and sex pheromone components containing acetate-ester functional groups, confirming its role as a broadly-tuned odorant degrading enzyme in the moth olfactory organ.