Conformational isomers of insect odorant-binding proteins

Understanding the Effects of Three Carbohydrate Feeds on the Health of Apis mellifera by Transcriptome Analysis

At present, there is no clear consensus on the impact of carbohydrate feeds on bee colony health, and comprehensive research and evaluation in this context is lacking. To comprehensively and objectively examine the health status of honeybees after consuming those carbohydrates from multiple perspectives, experimental techniques, including high-throughput sequencing of the transcriptome, proboscis extension reflex (PER), and measuring bee growth parameters were employed. This study showed that compared with honey, feeding high fructose syrup (HFS) resulted in a decrease in the survival rate and body weight of bees, while sucrose decreased the learning and memory ability of bees. After feeding on honey, the main antimicrobial peptides including abaecin, apidaecin1, hymenoptin, and defensin in bees, are all upregulated in expression. The 14 DEGs significantly enriched in the axonal regeneration pathway were all downregulated in the sucrose group and HFS group. This study demonstrated that the expression of multiple genes involved in oxidative phosphorylation was downregulated in bees fed with HFS, moreover, HFS also affected the biosynthesis of unsaturated fatty acids. These effects may lead to energy and metabolic disorders (including fatty acids), thereby inhibiting the growth and development of bees. Sucrose can decrease the learning and memory ability of bees, which may be due to the downregulation of genes related to learning and memory in the axonal regeneration pathway. Honey can upregulate antimicrobial peptides and other immune-related proteins, activating the bee's immune system and boosting bees' immunity to pathogens.

Variant A of the Deformed Wings Virus Alters the Olfactory Sensitivity and the Expression of Odorant Binding Proteins on Antennas of Apis mellifera

Simple Summary

Honey bees, Apis melllifera, are the most commonly managed bee in the world for pollination services. However, worldwide continuous colony losses have been reported for almost a decade. One factor of these losses is associated to pathogens being the virus one of the most important problems in honey bee health. One of the known viruses that affect the honey bee population is deformed wing virus (DWV). DWV causes physical malformation and behavioral disturbances, but also, this virus can be found in the antenna affecting the anatomical integrity of infected areas, which could compromise normal antennal functioning associated to aroma perception. Thus, we evaluate olfactory sensitivity and the expression of antenna-specific odorant-binding proteins (OBP) genes in honey bees inoculated with variant A of the DWV. We performed olfactory sensitivity analysis using the essential oils Eucalyptus globulus and Mentha piperita, but also, and molecular analysis of gene expression of nine OBPs. We found that the high level of replication of DWV-A in the antennae decreased the olfactory sensitivity and led to a down-regulation of some OBPs in middle- and forager-age worker bees. Thus, DWV-A infection in adults of honey bees could compromise volatile compound recognition inside the hive and outside the hive.

Abstract

Insects have a highly sensitive sense of smell, allowing them to perform complex behaviors, such as foraging and peer recognition. Their sense of smell is based on the recognition of ligands and is mainly coordinated by odorant-binding proteins (OBPs). In Apis mellifera, behavior can be affected by different pathogens, including deformed wing virus (DWV) and its variants. In particular, it has been shown that variant A of DWV (DWV-A) is capable of altering the ultra-cellular structure associated with olfactory activity. In this study was evaluated olfactory sensitivity and the expression of OBP genes in honey bees inoculated with DWV-A. Electroantennographic analyses (EAG) were carried out to determine the olfactory sensitivity to the essential oils Eucalyptus globulus and Mentha piperita. The expression of nine antenna-specific OBP genes and DWV-A load in inoculated bees was also quantified by qPCR. We observed an inverse relationship between viral load and olfactory sensitivity and the expression of some OBP proteins. Thus, high viral loads reduced olfactory sensitivity to essential oils and the gene expression of the OBP2, OBP5, OBP11, and OBP12 proteins on the antennas of middle- and forager-age bees. These results suggest that DWV-A could have negative effects on the processes of aroma perception by worker bees, affecting their performance in tasks carried out in and outside the colony.

A possible role of DNA methylation in functional divergence of a fast evolving duplicate gene encoding odorant binding protein 11 in the honeybee

Although gene duplication is seen as the main path to evolution of new functions, molecular mechanisms by which selection favours the gain versus loss of newly duplicated genes and minimizes the fixation of pseudo-genes are not well understood. Here, we investigate in detail a duplicate honeybee gene obp11 belonging to a fast evolving insect gene family encoding odorant binding proteins (OBPs). We report that obp11 is expressed only in female bees in rare antennal sensilla basiconica in contrast to its tandem partner obp10 that is expressed in the brain in both females and males (drones). Unlike all other obp genes in the honeybee, obp11 is methylated suggesting that functional diversification of obp11 and obp10 may have been driven by an epigenetic mechanism. We also show that increased methylation in drones near one donor splice site that correlates with higher abundance of a transcript variant encoding a truncated OBP11 protein is one way of controlling its contrasting expression. Our data suggest that like in mammals and plants, DNA methylation in insects may contribute to functional diversification of proteins produced from duplicated genes, in particular to their subfunctionalization by generating complementary patterns of expression.

Transcriptome and tissue-specific expression analysis of Obp and Csp genes in the dark black chafer

The dark black chafer, Holotrichia parallela, is an economically important pest in China and worldwide. Traps based on chemical communication are being developed as an alternative control measure to pesticides for this pest, and studies to reveal chemical communication mechanisms in this pest are highly desirable. To systematically analyze genes potentially involved in chemical communication in this pest, we generated a comprehensive transcriptome with combined samples derived from multiple tissues and developmental stages. A total of 43,967 nonredundant sequences (unigenes) with average length of 806 bp were obtained. These unigenes were annotated into different pathways using gene ontology analysis and cluster analysis of orthologous groups of proteins, and kyoto encyclopedia of genes and genomes. In total, 25 transcripts encoding odorant-binding proteins (OBPs) and 16 transcripts encoding chemosensory proteins (CSPs) were identified based on homology searches. Tissue-specific expression profile indicates that OBP17 and CSP7 are likely responsible for male sex pheromone recognition, whereas OBP1-4, OBP9, OBP13-14, OBP17-18, OBP20, OBP22, OBP25, CSP1-7, CSP11, and CSP12-15 are likely responsible for chemical communication between the beetle and environments. Our data shall provide a foundation for further research on the molecular aspects of chemical communication of this insect, and for comparative genomic studies with other species.

Molecular and biochemical characterization of two odorant-binding proteins from dark black chafer, Holotrichia parallela

The dark black chafer, Holotrichia parallela Motschulsky, is an economically important pest worldwide. Odorant-based lures and traps are being developed as a key kind of alternative control measures for this pest, and studies to reveal the mechanisms for chemotaxis in this pest are necessary. Two full-length cDNAs encoding different odorant-binding proteins (OBPs) were cloned. The predicted proteins were found to have the functional domains characteristic of typical OBPs and share a high degree of sequence similarity with OBP1 and OBP2 from other insects and were therefore designated as H. parallela OBP-1 and H. parallela OBP-2 (HparOBP-1 and HparOBP-2, respectively). These two OBPs were specifically expressed in antennae. The binding affinity of two purified proteins indicated that HparOBP-1 and HparOBP-2 could selectively interact with various volatiles emitted from host plants and pheromone components. Among the 10 chemicals tested, HparOBP-1 could bind to six of the tested compounds with a dissociation concentration (Ki) less than 20, and HparOBP-2 could bind to three of the compounds. The two OBPs are probably involved in chemotaxis of the dark black chafer. This discovery should accelerate research on chemical communications of this pest, which could potentially lead to the improvement of control measures based on lures and traps.

An insight into the sialome of the blood-sucking bug Triatoma infestans, a vector of Chagas' disease

Triatoma infestans is a hemiptera, vector of Chagas' disease that feeds exclusively on vertebrate blood in all life stages. Hematophagous insects' salivary glands (SG) produce potent pharmacological compounds that counteract host hemostasis, including anticlotting, antiplatelet, and vasodilatory molecules. To obtain a further insight into the salivary biochemical and pharmacological complexity of this insect, a cDNA library from its SG was randomly sequenced. Also, salivary proteins were submitted to two-dimensional gel (2D-gel) electrophoresis followed by MS analysis. We present the analysis of a set of 1534 (SG) cDNA sequences, 645 of which coded for proteins of a putative secretory nature. Most salivary proteins described as lipocalins matched peptide sequences obtained from proteomic results.

Function and evolution of a gene family encoding odorant binding-like proteins in a social insect, the honey bee (Apis mellifera)

The remarkable olfactory power of insect species is thought to be generated by a combinatorial action of two large protein families, G protein-coupled olfactory receptors (ORs) and odorant binding proteins (OBPs). In olfactory sensilla, OBPs deliver hydrophobic airborne molecules to ORs, but their expression in nonolfactory tissues suggests that they also may function as general carriers in other developmental and physiological processes. Here we used bioinformatic and experimental approaches to characterize the OBP-like gene family in a highly social insect, the Western honey bee. Comparison with other insects shows that the honey bee has the smallest set of these genes, consisting of only 21 OBPs. This number stands in stark contrast to the more than 70 OBPs in Anopheles gambiae and 51 in Drosophila melanogaster. In the honey bee as in the two dipterans, these genes are organized in clusters. We show that the evolution of their structure involved frequent intron losses. We describe a monophyletic subfamily of OBPs where the diversification of some amino acids appears to have been accelerated by positive selection. Expression profiling under a wide range of conditions shows that in the honey bee only nine OBPs are antenna-specific. The remaining genes are expressed either ubiquitously or are tightly regulated in specialized tissues or during development. These findings support the view that OBPs are not restricted to olfaction and are likely to be involved in broader physiological functions.

An odorant-binding protein facilitates odorant transfer from air to hydrophilic surroundings in the blowfly

Chemical sense-related lipophilic ligand-binding protein (CRLBP) is an insect odorant-binding protein (OBP) found abundantly in the taste and olfactory organs of the blowfly, Phormia regina. Through computational construction, a three-dimensional molecular model of a CRLBP indicated good fitting to a fluorescent ligand, 7-hydroxycoumarin (7-HC), in its ligand-binding pocket. By showing that the fluorescence of 7-HC bound to CRLBP migrated in a native electrophoresis gel, we confirmed that CRLBP formed a stable complex with 7-HC. In an odorant-binding experiment, 7-HC vapor odor was introduced by aeration to the aquatic solution containing CRLBP and its binding to CRLBP fluorospectrometrically quantified. Because olfactory organs as well as taste organs of flies respond to vapors, we suggest that CRLBP effectively transfers odorants from the air into aquatic surroundings by forming stable complexes with airborne molecules in both chemosensory organs.

Identification and molecular cloning of putative odorant-binding proteins from the American palm weevil, Rhynchophorus palmarum L

We have identified and cloned the cDNAs encoding two odorant-binding proteins (OBPs) from the American palm weevil (APW) Rhynchophorus palmarum (Coleoptera, Curculionidae). Degenerate primers were designed from the N-terminal sequences and were used in polymerase chain reaction (PCR) in order to obtain full-length sequences in both males and females. In both sexes, two different cDNAs were obtained, encoding 123 and 115 amino acid-deduced sequences. Each sequence showed few amino acid differences between the sexes. The proteins were named RpalOBP2 and RpalOBP4 for male, RpalOBP2' and RpalOBP4' for female, with the types 2 and 4 presenting only 34% identities. These proteins shared high identity with previously described coleopteran OBPs. In native gels, RpalOBP2 clearly separated into two bands and RpalOBP4 into three bands, suggesting the presence of several conformational isomers. Thus, OBP diversity in this species may rely on both the presence of OBPs from different classes and the occurrence of isoforms for each OBP.

Persistent Conformational Heterogeneity of Triosephosphate Isomerase: Separation and Characterization of Conformational Isomers in Solution

Subunit dissociation of dimeric rabbit muscle triosephosphate isomerase (TIM) by hydrostatic pressure has previously been shown not to follow the expected dependence on protein concentration [Rietveld and Ferreira (1996) Biochemistry 35, 7743-7751]. This anomalous behavior was attributed to persistent conformational heterogeneity (i.e., the coexistence of long-lived conformational isomers) in the ensemble of TIM dimers. Here, we initially show that subunit dissociation/unfolding of TIM by guanidine hydrochloride (GdnHCl) also exhibits an anomalous dependence on protein concentration. Dissociation/unfolding of TIM by GdnHCl was investigated by intrinsic fluorescence and circular dichroism spectroscopies and was found to be a highly cooperative transition in which the tertiary and secondary structures of the protein were concomitantly lost. A procedure based on size-exclusion chromatography in the presence of intermediate (0.6 M) GdnHCl concentrations was developed to isolate two conformational isomers of TIM that exhibit significantly different stabilities and kinetics of unfolding by GdnHCl. Complete unfolding of the two isolated conformers at a high GdnHCl concentration (1.5 M), followed by refolding by removal of the denaturant, completely abolished the differences in their unfolding kinetics. These results indicate that such differences stem from conformational heterogeneity of TIM and are not related to any chemical modification of the protein. Furthermore, they add support to the notion that long-lived conformational isomers of TIM coexist in solution and provide a basis for the interpretation of the persistent heterogeneity of this protein.

Odorant-binding proteins from a primitive termite

Hitherto, odorant-binding proteins (OBPs) have been identified from insects belonging to more highly evolved insect orders (Lepidoptera, Coleoptera, Diptera, Hymenoptera, and Hemiptera), whereas only chemosensory proteins have been identified from more primitive species, such as orthopteran and phasmid species. Here, we report for the first time the isolation and cloning of odorant-binding proteins from a primitive termite species, the dampwood termite. Zootermopsis nevadensis nevadensis (Isoptera: Termopsidae). A major antennae-specific protein was detected by native PAGE along with four other minor proteins, which were also absent in the extract from control tissues (hindlegs). Multiple cDNA cloning led to the full characterization of the major antennae-specific protein (ZnevOBP1) and to the identification of two other antennae-specific cDNAs, encoding putative odorant-binding proteins (ZnevOBP2 and ZnevOBP3). N-terminal amino acid sequencing of the minor antennal bands and cDNA cloning showed that olfaction in Z. n. nevadensis may involve multiple odorant-binding proteins. Database searches suggest that the OBPs from this primitive termite are homologues of the pheromone-binding proteins from scarab beetles and antennal-binding proteins from moths.

Identification and cloning of a female antenna-specific odorant-binding protein in the mosquito Culex quinquefasciatus

We have identified and cloned a cDNA encoding the first odorant-binding protein isolated from mosquitoes. The protein isolated from female antennae of Culex quinquefasciatus (CquiOBP) was not detected in legs (control tissue) or in antennal extracts from males, and showed mobility in native polyacrylamide gels similar to that of the pheromone-binding protein from Bombyx mori. The open reading frame of the cloned cDNA encoded a hydrophobic signal peptide (24 residues) and an acid mature protein (pI 5.5) of 125 amino acid residues (calculated molecular mass 14,504 Da). The transcript was detected by RT-PCR with antennal, but not with leg tissues. CquiOPB shared the highest amino acid identity with a product deduced from Drosophila melanogaster PBPRP-3 cDNA (58.6%), OBPs from scarab beetles (35%), and moths (28%). In addition, CquiOBP showed the hallmark of insect odorant-binding proteins, the six Cys residues.