Various Bee Pheromones Binding Affinity, Exclusive Chemosensillar Localization, and Key Amino Acid Sites Reveal the Distinctive Characteristics of Odorant-Binding Protein 11 in the Eastern Honey Bee, Apis cerana

Abstract

Odorant-binding proteins (OBPs) are the critical elements responsible for binding and transporting odors and pheromones in the sensitive olfactory system in insects. Honey bees are representative social insects that have complex odorants and pheromone communication systems relative to solitary insects. Here, we first cloned and characterized OBP11 (AcerOBP11), from the worker bees antennae of Eastern honey bee, Apis cerana. Based on sequence and phylogenetic analysis, most sequences homologous to AcerOBP11 belong to the typical OBPs family. The transcriptional expression profiles showed that AcerOBP11 was expressed throughout the developmental stages and highly specifically expressed in adult antennae. Using immunofluorescence localization, AcerOBP11 in worker bee's antennae was only localized in the sensilla basiconica (SB) near the fringe of each segment. Fluorescence ligand-binding assay showed that AcerOBP11 protein had strong binding affinity with the tested various bee pheromones components, including the main queen mandibular pheromones (QMPs), methyl p-hydroxybenzoate (HOB), and (E)-9-oxo-2-decanoic acid (9-ODA), alarm pheromone (n-hexanol), and worker pheromone components. AcerOBP11 also had strong binding affinity to plant volatiles, such as 4-Allylveratrole. Based on the docking and site-directed mutagenesis, two key amino acid residues (Ile97 and Ile140) were involved in the binding of AcerOBP11 to various bee pheromones. Taken together, we identified that AcerOBP11 was localized in a single type of antennal chemosensilla and had complex ligand-binding properties, which confer the dual-role with the primary characteristics of sensing various bee pheromones and secondary characteristics of sensing general odorants. This study not only prompts the theoretical basis of OBPs-mediated bee pheromones recognition of honey bee, but also extends the understanding of differences in pheromone communication between social and solitary insects.

Expression Profile and Ligand Screening of a Putative Odorant-Binding Protein, AcerOBP6, from the Asian Honeybee

“…In other words, AcerOBP6 was a broad-spectrum binding protein, which had similar binding properties to those of other insect OBPs, such as AipsGOBP1 and AlepGOBP2 [31,32]. At the same time, several studies had reported OBP functions in A. cerana cerana including AcerOBP1, AcerOBP10, AcerOBP11, and AcerOBP15, in which AcerOBP1 and AcerOBP15 were the proteins that were mainly involved in pheromone binding [19,21,33,34]. In addition, this binding characteristic of AcerOBP6 was also consistent with the structure of the PBP-GOBP domain.…”

“…AmelOBP14 is better tuned to monoterpenoid structures, and AmelOBP21 will bind the main components of the queen mandibular pheromone as well as farnesol [18]. Apart from that, AcerOBP11 could bind to bee pheromones and some floral volatiles [19]. According to a recent study, AcerOBP10 is involved in oxidative stress defense [20], and myrcene may be a ligand of AcerOBP15 [21].…”

Expression, Affinity, and Functional Characterization of the Specific Binding of Two Putative Pheromone-Binding Proteins in the Omnivorous German Cockroach Blattella germanica

“…PBP1 has a strong affinity for the (−)-enantiomer, while PBP2 has a higher affinity for the (+)-enantiomer. Furthermore, AcerOBP11 of the eastern honey bee, Apis cerana , also displayed distinct binding affinities with various similar pheromone components …”

Olfactory coding in honeybees

“…Volatile molecules reaching the honeybee antennae enter the sensillar pores and diffuse through the sensillar lymph until they reach the OSNs’ dendritic membrane. The sensillar lymph prevents the OSNs’ dendritic terminals from drying, and contains olfactory binding proteins (OBPs) and odorant degrading enzymes (ODEs) (Chertemps et al 2015 ; Forêt and Maleszka 2006 ; Iovinella et al 2018 ; Song et al 2018 ; Vogt et al 1991 ; Younus et al 2014 ). OBPs are likely involved in facilitating the transition of the odorants from a gaseous to a liquid environment and in transporting them towards the olfactory receptors (Gomez-Diaz et al 2013 ; Laughlin et al 2008 ; Leal 2013 ), even if recent studies in Drosophila showed that deletion of the principal OBP genes does not impair odor transduction, suggesting that many OBP may not play an essential role in odorant-receptor interaction (Xiao et al 2019 ).…”