Odorant-binding proteins and chemosensory proteins in pheromone detection and release in the silkmoth Bombyx mori

The genome of the silkmoth Bombyx mori contains 44 genes encoding odorant-binding proteins (OBPs) and 20 encoding chemosensory proteins (CSPs). In this work, we used a proteomic approach to investigate the expression of proteins of both classes in the antennae of adults and in the female pheromone glands. The most abundant proteins found in the antennae were the 4 OBPs (PBP, GOBP1, GOBP2, and ABP) and the 2 CSPs (CSP1 and CSP2) previously identified and characterized. In addition, we could detect only 3 additional OBPs and 2 CSPs, with clearly different patterns of expression between the sexes. Particularly interesting, on the other hand, is the relatively large number of binding proteins (1 OBP and 7 CSPs) expressed in the female pheromone glands, some of them not present in the antennae. In the glands, these proteins could be likely involved in the solubilization of pheromonal components and their delivery in the environment.     

Expression of odorant-binding proteins and chemosensory proteins in some Hymenoptera

The expression of chemosensory proteins (CSPs) and odorant-binding proteins (OBPs) in individuals of different castes and ages have been monitored in three species of social hymenopterans, Polistes dominulus (Hymenoptera, Vespidae), Vespa crabro (Hymenoptera, Vespidae) and Apis mellifera (Hymenoptera, Apidae), using PCR with specific primers and polyclonal antibodies. In the paper wasp P. dominulus, OBP is equally expressed in antennae, wings and legs of all castes and ages, while CSP is often specifically present in antennae and in some cases also in legs. In the vespine species V. crabro CSP is antennal specific, while OBP is also expressed in legs and wings. The three CSPs and the five OBPs of A. mellifera show a complex pattern of expression, where both classes of proteins include members specifically expressed in antennae and others present in other parts of the body. These data indicate that at least in some hymenopteran species CSPs are specifically expressed in antennae and could perform roles in chemosensory perception so far assigned only to OBPs.     

Comparative genomics and transcriptomics in ants provide new insights into the evolution and function of odorant binding and chemosensory proteins

Background

The complex societies of ants and other social insects rely on sophisticated chemical communication. Two families of small soluble proteins, the odorant binding and chemosensory proteins (OBPs and CSPs), are believed to be important in insect chemosensation. To better understand the role of these proteins in ant olfaction, we examined their evolution and expression across the ants using phylogenetics and sex- and tissue-specific RNA-seq.

Results

We find that subsets of both OBPs and CSPs are expressed in the antennae, contradicting the previous hypothesis that CSPs have replaced OBPs in ant olfaction. Both protein families have several highly conserved clades with a single ortholog in all eusocial hymenopterans, as well as clades with more dynamic evolution and many taxon-specific radiations. The dynamically evolving OBPs and CSPs have been hypothesized to function in chemical communication. Intriguingly, we find that seven members of the conserved clades are expressed specifically in the antennae of the clonal raider ant Cerapachys biroi, whereas only one dynamically evolving CSP is antenna specific. The orthologs of the conserved, antenna-specific C. biroi genes are also expressed in antennae of the ants Camponotus floridanus and Harpegnathos saltator, indicating that antenna-specific expression of these OBPs and CSPs is conserved across ants. Most members of the dynamically evolving clades in both protein families are expressed primarily in non-chemosensory tissues and thus likely do not fulfill chemosensory functions.

Conclusions

Our results identify candidate OBPs and CSPs that are likely involved in conserved aspects of ant olfaction, and suggest that OBPs and CSPs may not rapidly evolve to recognize species-specific signals.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-718) contains supplementary material, which is available to authorized users.     

Differential expression of odorant-binding proteins in the mandibular glands of the honey bee according to caste and age

Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) mediate both perception and release of chemical stimuli in insects. The genome of the honey bee contains 21 genes encoding OBPs and 6 encoding CSPs. Using a proteomic approach, we have investigated the expression of OBPs and CSPs in the mandibular glands of adult honey bees in relation to caste and age. OBP13 is mostly expressed in young individuals and in virgin queens, while OBP21 is abundant in older bees and is prevalent in mated queens. OBP14, which had been found in larvae, is produced in hive workers' glands. Quite unexpectedly, the mandibular glands of drones also contain OBPs, mainly OBP18 and OBP21. We have expressed three of the most represented OBPs and studied their binding properties. OBP13 binds with good specificity oleic acid and some structurally related compounds, OBP14 is better tuned to monoterpenoid structures, while OBP21 binds the main components of queen mandibular pheromone as well as farnesol, a compound used as a trail pheromone in the honey bee and other hymenopterans. The high expression of different OBPs in the mandibular glands suggests that such proteins could be involved in solubilization and release of semiochemicals.     

Crystal and Solution Studies of the “Plus-C” Odorant-binding Protein 48 from Anopheles gambiae: CONTROL OF BINDING SPECIFICITY THROUGH THREE-DIMENSIONAL DOMAIN SWAPPING*

Much physiological and behavioral evidence has been provided suggesting that insect odorant-binding proteins (OBPs) are indispensable for odorant recognition and thus are appealing targets for structure-based discovery and design of novel host-seeking disruptors. Despite the fact that more than 60 putative OBP-encoding genes have been identified in the malaria vector Anopheles gambiae, the crystal structures of only six of them are known. It is therefore clear that OBP structure determination constitutes the bottleneck for structure-based approaches to mosquito repellent/attractant discovery. Here, we describe the three-dimensional structure of an A. gambiae “Plus-C” group OBP (AgamOBP48), which exhibits the second highest expression levels in female antennae. This structure represents the first example of a three-dimensional domain-swapped dimer in dipteran species. A combined binding site is formed at the dimer interface by equal contribution of each monomer. Structural comparisons with the monomeric AgamOBP47 revealed that the major structural difference between the two Plus-C proteins localizes in their N- and C-terminal regions, and their concerted conformational change may account for monomer-swapped dimer conversion and furthermore the formation of novel binding pockets. Using a combination of gel filtration chromatography, differential scanning calorimetry, and analytical ultracentrifugation, we demonstrate the AgamOBP48 dimerization in solution. Eventually, molecular modeling calculations were used to predict the binding mode of the most potent synthetic ligand of AgamOBP48 known so far, discovered by ligand- and structure-based virtual screening. The structure-aided identification of multiple OBP binders represents a powerful tool to be employed in the effort to control transmission of the vector-borne diseases.     

冈比亚按蚊嗅觉结合蛋白候选基因cDNA的克隆、鉴定及其表达型分析

疟蚊主要依靠嗅觉发现寄主。非洲疟蚊冈比亚按蚊Anopheles gambiae是一种嗜吸人血的疟疾传播媒介昆虫。该文作者基于其全基因组序列,采用RT-PCR和标准分子克隆技术获得2个嗅觉结合蛋白候选基因agLZ3788和agLZ9988。测序分析结果表明,它们具有嗅觉结合蛋白的标志性结构域。进一步采用半定量RT-PCR技术研究了它们的空间表达型,结果发现它们不但在雌蚊触角中表达,也在其他部位(尤其是蚊虫足部)有强的表达。这一发现说明疟蚊嗅觉结合蛋白可能具有更广的功能,也为进一步重组表达和功能研究提供了重要依据。     

Expression pattern analysis of odorant‐binding proteins in the pea aphid Acyrthosiphon pisum

Odorant‐binding proteins (OBPs) are soluble proteins mediating chemoreception in insects. In previous research, we investigated the molecular mechanisms adopted by aphids to detect the alarm pheromone (E)‐β‐farnesene and we found that the recognition of this and structurally related molecules is mediated by OBP3 and OBP7. Here, we show the differential expression patterns of 5 selected OBPs (OBP1, OBP3, OBP6, OBP7, OBP8) obtained performing quantitative RT‐PCR and immunolocalization experiments in different body parts of adults and in the 5 developmental instars, including winged and unwinged morphs, of the pea aphid Acyrthosiphon pisum. The results provide an overall picture that allows us to speculate on the relationship between the differential expression of OBPs and their putative function. The expression of OBP3, OBP6, and OBP7 in the antennal sensilla suggests a chemosensory function for these proteins, whereas the constant expression level of OBP8 in all instars could suggest a conserved role. Moreover, OBP1 and OBP3 are also expressed in nonsensory organs. A light and scanning electron microscopy study of sensilla on different body parts of aphid, in particular antennae, legs, mouthparts, and cornicles‐cauda, completes this research providing a guide to facilitate the mapping of OBP expression profiles.     

New insights into the mechanism of odorant detection by the malaria-transmitting mosquito Anopheles gambiae

Anopheles gambiae mosquitoes that transmit Plasmodium falciparum malaria use a series of olfactory cues present in human sweat to locate their hosts for a blood meal. Recognition of these odor cues occurs through the interplay of odorant receptors and odorant-binding proteins (OBPs) that bind to odorant molecules and transport and present them to the receptors. Recent studies have implicated potential heterodimeric interactions between two OBPs, OBP1 and OBP4, as important for perception of indole by the mosquito (Biessmann, H., Andronopoulou, E., Biessmann, M. R., Douris, V., Dimitratos, S. D., Eliopoulos, E., Guerin, P. M., Iatrou, K., Justice, R. W., Kröber, T., Marinotti, O., Tsitoura, P., Woods, D. F., and Walter, M. F. (2010) PLoS ONE 5, e9471; Qiao, H., He, X., Schymura, D., Ban, L., Field, L., Dani, F. R., Michelucci, E., Caputo, B., della Torre, A., Iatrou, K., Zhou, J. J., Krieger, J., and Pelosi, P. (2011) Cell. Mol. Life Sci. 68, 1799–1813). Here we present the 2.0 Å crystal structure of the OBP4-indole complex, which adopts a classical odorant-binding protein fold, with indole bound at one end of a central hydrophobic cavity. Solution-based NMR studies reveal that OBP4 exists in a molten globule state and binding of indole induces a dramatic conformational shift to a well ordered structure, and this leads to the formation of the binding site for OBP1. Analysis of the OBP4-OBP1 interaction reveals a network of contacts between residues in the OBP1 binding site and the core of the protein and suggests how the interaction of the two proteins can alter the binding affinity for ligands. These studies provide evidence that conformational ordering plays a key role in regulating heteromeric interactions between OBPs.