A sublethal dose of neonicotinoid imidacloprid precisely sensed and detoxified by a C-minus odorant-binding protein 17 highly expressed in the legs of Apis cerana.

As a native honeybee species in East Asia, Apis cerana is essential for the stability of local agricultural and plant ecosystems by its' olfactory system for searching nectar and pollen sources. Odorant-binding proteins (OBPs) existing in the insect's olfactory system can recognize environmental semiochemicals. It was known that sublethal doses of neonicotinoid insecticides could still cause a variety of physiological and behavioral abnormalities in bees. However, the molecular mechanism of A. cerana sensing and response for insecticide has not been further investigated. In this study, we found an A. cerana OBP17 gene significantly up-regulated expressed after exposure to sublethal doses of imidacloprid based on the transcriptomics results. The spatiotemporal expression profiles showed that OBP17 was highly expressed in the legs. Competitive fluorescence binding assays showed that OBP17 had the special and high binding affinity to imidacloprid among the 24 candidate semiochemicals, and the KA value of OBP17 binding with imidacloprid reached the maximum (6.94 × 104 L/mol) at low-temperature. Thermodynamic analysis showed that the quenching mechanism changed from dynamic to static binding interaction with the increasing temperature. Meanwhile, the force changed from hydrogen bond and van der Waals force to hydrophobic interaction and electrostatic force, indicating the interaction exhibits variability and flexibility. Molecular docking showed that Phe107 contributed the most energy. RNA interference (RNAi) results showed that OBP17 knockdown significantly enhanced the electrophysiological response of the bees' forelegs to imidacloprid. Our study indicated that OBP17 could precisely touch and sense sublethal doses of neonicotinoid imidacloprid in the natural environment through its high expression in legs, and the upregulation expression of OBP17 exposure to imidacloprid probably implied that it participate in the detoxification processes of A. cerana. Also, our research enriches the theoretical knowledge of the sensing and detoxifying activities of non-target insects' olfactory sensory system to environmental sublethal doses of systemic insecticides.

Unique dynamic mode between Artepillin C and human serum albumin implies the characteristics of Brazilian green propolis representative bioactive component.

As a representative bioactive component in Brazil green propolis, Artepillin C (ArtC; 3, 5-diprenyl-4-hydroxycinnamic acid) has been reported a wide variety of physiological activities including anti-tumor, anti-inflammatory, and antimicrobial activity etc. However, it seems incompatible that ArtC in vivo was characterized as low absorption efficiency and low bioavailability. In order to obtain the elucidation, we further investigated the physicochemical basis of ArtC interacting with human serum albumin (HSA) in vitro. We found a unique dynamic mode interaction between ArtC and HSA, which is completely different from other reported propolis bioactive components. Thermodynamic analysis showed that hydrophobic interactions and electrostatic forces are the main driving force. The competitive assay indicates that the binding site of ArtC with HSA is close to the Sudlow's site I. The findings of this study reveal the unique physicochemical transport mechanism of ArtC in the human body, which helps to further understand the uniqueness of the representative functional components of Brazilian green propolis in the human body.

Chemical structure of semiochemicals and key binding sites together determine the olfactory functional modes of odorant-binding protein 2 in Eastern honey bee, Apis cerana.

Insects can exhibit flexible olfaction that is sensitive to complex natural chemical environments. Odorant-binding proteins (OBPs) in insects' antennal chemosensilla can act as transporters of plant volatiles and pheromones across the sensillar lymph. Although the physiological functions of OBPs have been widely reported, it is still unclear how OBP binds to ligands with various structures in detail. Here, we further investigated the ligand-binding modes and characteristics of AcerOBP2 from the Eastern honey bee (Apis cerana). The results showed that, as a specific protein distributed below the base of chemosensilla on the antennal surface, AcerOBP2 was strongly bound with the candidate floral volatiles and bee pheromones. By docking analysis and site-directed mutagenesis, four different binding modes were found in the five AcerOBP2 mutants between six ligands. Two key amino acids, Ser123 and Lys51, play a key role in AcerOBP2 binding to odors, depending on the presence or absence of hydrogen bonds. In addition, the binding modes depend on their chemical structures and the binding poses of the diverse ligands. These results not only further prompted the functional basis of the relationship between the chemical structures of odorants and bee OBPs, but also revealed the complexity of the flexible behavioral modes of odor binding in insect olfactory systems.

Physicochemical Basis and Comparison of Two Type II Sex Pheromone Components Binding with Pheromone-Binding Protein 2 from Tea Geometrid, Ectropis obliqua.

Lepidopteran geometrid moth can produce complex Type II sex pheromone components to attract males and trigger mating behavior. Although several sex pheromone components have been identified, it remains unclear whether their physicochemical roles in sex pheromone sensing are the same. Therefore, we utilized tea geometrid ( Ectropis obliqua) as an example model to investigate and compare the physicochemical basis of two key Type II sex pheromone components, cis-6,7-epoxy-(3Z,9Z)-3,9-octadecadiene ( Z3 Z9-6,7-epo-18:Hy) and ( Z, Z, Z)-3,6,9-octadecatriene (Z3Z6Z9-18:Hy), interacting with pheromone-binding protein 2 ( EoblPBP2) from E. obliqua. Multispectral, thermodynamic, docking, and site-directed mutagenesis indicated that the major sex pheromone component Z3Z9-6,7-epo-18:Hy is more susceptible to pH-tuned than the minor component Z3Z6Z9-18:Hy, whereas Z3Z6Z9-18:Hy seems to be more susceptible to temperature and amino acid mutations than Z3Z9-6,7-epo-18:Hy. Our study suggests that different components of Type II sex pheromone play different binding characters under specific conditions in the physicochemical behavior. This deeply supplements the theoretical knowledge of Type II pheromones involved in the recognition and discrimination in the Lepidopteran sex pheromones family.