Journal Article

Putative ligand binding sites of two functionally characterized bark beetle odorant receptors

Machara, Aleš, Roberts, Rebecca E., Hansson, Bill S., Yuvaraj, Jothi K., Sonntag, Yonathan, Hou, Xiao-Qing, Zhang, Dan-Dan, Löfstedt, Christer, Johanson, Urban, Grosse-Wilde, Ewald, Andersson, Martin N.

2021

Overview

Background Bark beetles are major pests of conifer forests, and their behavior is primarily mediated via olfaction. Targeting the odorant receptors (ORs) may thus provide avenues towards improved pest control. Such an approach requires information on the function of ORs and their interactions with ligands, which is also essential for understanding the functional evolution of these receptors. Hence, we aimed to identify a high-quality complement of ORs from the destructive spruce bark beetle Ips typographus (Coleoptera, Curculionidae, Scolytinae) and analyze their antennal expression and phylogenetic relationships with ORs from other beetles. Using 68 biologically relevant test compounds, we next aimed to functionally characterize ecologically important ORs, using two systems for heterologous expression. Our final aim was to gain insight into the ligand-OR interaction of the functionally characterized ORs, using a combination of computational and experimental methods. Results We annotated 73 ORs from an antennal transcriptome of I. typographus and report the functional characterization of two ORs (ItypOR46 and ItypOR49), which are responsive to single enantiomers of the common bark beetle pheromone compounds ipsenol and ipsdienol, respectively. Their responses and antennal expression correlate with the specificities, localizations, and/or abundances of olfactory sensory neurons detecting these enantiomers. We use homology modeling and molecular docking to predict their binding sites. Our models reveal a likely binding cleft lined with residues that previously have been shown to affect the responses of insect ORs. Within this cleft, the active ligands are predicted to specifically interact with residues Tyr84 and Thr205 in ItypOR46. The suggested importance of these residues in the activation by ipsenol is experimentally supported through site-directed mutagenesis and functional testing, and hydrogen bonding appears key in pheromone binding. Conclusions The emerging insight into ligand binding in the two characterized ItypORs has a general importance for our understanding of the molecular and functional evolution of the insect OR gene family. Due to the ecological importance of the characterized receptors and widespread use of ipsenol and ipsdienol in bark beetle chemical communication, these ORs should be evaluated for their potential use in pest control and biosensors to detect bark beetle infestations.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Analysis / Animals / Bark / Bark beetles / Beetles / Binding Sites / Biologi / Biological Sciences / Biomedical and Life Sciences / Biosensors / Chemical communication / Chemical ecology / Coleoptera / Coniferous forests / Deorphanization / Diseases and pests / Ecology (including Biodiversity Conservation) / Ekologi / Enantiomers / Evolution / Evolutionary Biology / Evolutionsbiologi / Experimental methods / Female / Functional evolution / Functional testing / Gene expression / Genes / Genetics and Genomics / Genetik och genomik / HEK293 cells / Homology / Hydrogen bonding / Identification and classification / Insect Proteins - chemistry / Insect Proteins - genetics / Insects / Life Sciences / Ligands / Male / Molecular docking / Natural Sciences / Naturvetenskap / Odorant receptor / Odorant receptors / Olfaction / Olfactory receptor neurons / Pest control / Pest insect / Pests / Pheromone receptor / Pheromones / Phylogenetics / Phylogeny / Prevention / Receptors / Receptors, Odorant - chemistry / Receptors, Odorant - genetics / Research Article / Residues / Sensory neurons / Site-directed mutagenesis / Transcriptomes / Weevils - chemistry / Weevils - genetics