Soluble proteins from chemosensory organs of Eurycantha calcarata (Insects, Phasmatodea)

Chemosensory proteins as putative semiochemical carriers in the desert isopod Hemilepistus reaumurii

The order Isopoda contains both aquatic and terrestrial species, among which Hemilepistus reaumurii, which lives in arid environments and is the most adapted to terrestrial life. Olfaction has been deeply investigated in insects while it has received very limited attention in other arthropods, particularly in terrestrial crustaceans. In insects, soluble proteins belonging to two main families, Odorant Binding Proteins (OBPs) and Chemosensory Proteins (CSPs), are contained in the olfactory sensillar lymph and are suggested to act as carriers of hydrophobic semiochemicals to or from membrane-bound olfactory receptors. Other protein families, namely Nieman-Pick type 2 (NPC2) and Lipocalins (LCNs) have been also reported as putative odorant carriers in insects and other arthropod clades. In this study, we have sequenced and analysed the transcriptomes of antennae and of the first pair of legs of H. reaumurii focusing on soluble olfactory proteins. Interestingly, we have found 13 genes encoding CSPs, whose sequences differ from those of the other arthropod clades, including non-isopod crustaceans, for the presence of two additional cysteine residues, besides the four conserved ones. Binding assays on two of these proteins showed strong affinities for fatty acids and long-chain unsaturated esters and aldehydes, putative semiochemicals for this species.

Identification and ligand binding of a chemosensory protein from sea louse Caligus rogercresseyi (Crustacea: Copepoda)

Caligus rogercresseyi is an ectoparasitic copepod that negatively affects the salmon farming industry, causing economic losses. To use phytochemicals as feed additives, or other chemicals that could elicit behavioral responses in C. rogercresseyi, the chemosensory recognition process is crucial. Therefore, to establish how C. rogercresseyi recognizes glucosinolates and their derivates isothiocyanates, a chemosensory protein (CSP) described as specific carrier of these chemicals in sea louse (CrogCSP) was identified in this study. The recombinant CSP and its selectivity against different chemical compounds was tested by fluorescence binding assays. Phylogenetic analysis revealed a close relationship among CrogCSP and other reported CSPs. Our results indicate that phenyl isothiocyanate and isophorone exhibited dissociation constants of 4.17 and 4.28 μM of K_i, respectively, indicating affinity over other chemicals, such as fatty acids and sinigrin. Structural findings suggest a unique binding site capable of accept several types of chemicals, similar to what has been reported for crystallized insect CSPs. Finally, this study lays the foundation for a deeper understanding of CSPs in crustaceans and especially in C. rogercresseyi. Likewise, the identification of chemosensory proteins could serve as the first step towards novel semiochemicals discovery to being applied in the sea louse controlling.

Expression Profiles and Binding Properties of the Chemosensory Protein PxylCSP11 from the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) is one of the most destructive pests to cruciferous plants worldwide. The oligophagous moth primarily utilizes its host volatiles for foraging and oviposition. Chemosensory proteins (CSPs) are soluble carrier proteins with low molecular weight, which recognize and transport various semiochemicals in insect chemoreception. At present, there is limited information on the recognition of host volatiles by CSPs of P. xylostella. Here, we investigated expression patterns and binding characteristics of PxylCSP11 in P. xylostella. The open reading frame of PxylCSP11 was 369-bp encoding 122 amino acids. PxylCSP11 possessed four conserved cysteines, which was consistent with the typical characteristic of CSPs. PxylCSP11 was highly expressed in antennae, and the expression level of PxylCSP11 in male antennae was higher than that in female antennae. Fluorescence competitive binding assays showed that PxylCSP11 had strong binding abilities to several ligands, including volatiles of cruciferous plants, and (Z)-11-hexadecenyl acetate (Z11-16:Ac), a major sex pheromone of P. xylostella. Our results suggest that PxylCSP11 may play an important role in host recognition and spouse location in P. xylostella.

A Chemosensory Protein BtabCSP11 Mediates Reproduction in Bemisia tabaci

The olfactory system serves a vital role in the evolution and survival of insects, being involved in behaviors such as host seeking, foraging, mating, and oviposition. Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are involved in the olfactory recognition process. In this study, BtabCSP11, a CSP11 gene from the whitefly Bemisia tabaci, was cloned and characterized. The open reading frame of BtabCSP11 encodes 136 amino acids, with four highly conserved cysteine residues. The temporal and spatial expression profiles showed that BtabCSP11 was highly expressed in the abdomens of B. tabaci females. Dietary RNA interference (RNAi)-based functional analysis showed substantially reduced fecundity in parthenogenetically reproduced females, suggesting a potential role of BtabCSP11 in B. tabaci reproduction. These combined results expand the function of CSPs beyond chemosensation.

Analysis of post-translational modifications in soluble proteins involved in chemical communication from mammals and insects

Different soluble, small polypeptide molecules isolated from biological tissues/body fluids of mammals and insects have been reported to bind odorant compounds and pheromones, and have been accordingly named odorant-binding proteins, pheromone-binding proteins and chemosensory proteins. Mammal and insect odorant-binding and pheromone-binding proteins show evident differences in their primary structure; in insects, the same condition occurs for odorant- and pheromone-binding proteins, which belong to the same protein family, and chemosensory proteins. In order to understand their molecular characteristics, these proteins have been subjected to an extensive analysis for their post-translational modifications through mass spectrometry approaches. Depending on proteins, they have been characterized as having specific disulfide bridge arrangements, which were consistent among molecular sequence homologs. Only selected odorant-binding proteins from mammals have been demonstrated bearing N-linked glycan structures and other modifications. In this review article, we discuss the application of mass spectrometry procedures for the analysis of post-translational modifications in odorant-binding proteins, pheromone-binding proteins and chemosensory proteins. Different example proteins are reported, and protocols are presented for obtaining definitive information in this context.

OcomCSP12, a Chemosensory Protein Expressed Specifically by Ovary, Mediates Reproduction in Ophraella communa (Coleoptera: Chrysomelidae)

Chemosensory proteins (CSPs) are considered to be the transporter linking odorant chemicals and receptors on sensory neurons. However, the extensive expression patterns of CSPs in insects suggest that CSPs are also involved in other physiological processes; the range of their functions, however, remains uncertain. In this study, we successfully characterized and cloned the CSP12 of Ophraella communa (OcomCSP12). The open reading frame of OcomCSP12 encodes 131 amino acids, with four conserved cysteine residues. The expression patterns of OcomCSP12 validated by quantitative real-time PCR (qRT-PCR) showed that OcomCSP12 is specifically expressed in female ovary. Furthermore, compared with the control treatment, silencing OcomCSP12 resulted in significantly reduced oviposition in females. Surprisingly, the knock-down rate of OcomCSP12 exceeded 95% and remained depressed for more than 15 days, indicating that RNA interference (RNAi) was a suitable method for exploring the function of CSP12 in O. communa. These findings increase our understanding of the expression profile and function of the CSP gene family in insects.

Odorant-Binding Proteins as Sensing Elements for Odour Monitoring

Odour perception has been the object of fast growing research interest in the last three decades. Parallel to the study of the corresponding biological systems, attempts are being made to model the olfactory system with electronic devices. Such projects range from the fabrication of individual sensors, tuned to specific chemicals of interest, to the design of multipurpose smell detectors using arrays of sensors assembled in a sort of artificial nose. Recently, proteins have attracted increasing interest as sensing elements. In particular, soluble olfaction proteins, including odorant-binding proteins (OBPs) of vertebrates and insects, chemosensory proteins (CSPs) and Niemann-Pick type C2 (NPC2) proteins possess interesting characteristics for their use in sensing devices for odours. In fact, thanks to their compact structure, their soluble nature and small size, they are extremely stable to high temperature, refractory to proteolysis and resistant to organic solvents. Moreover, thanks to the availability of many structures solved both as apo-proteins and in complexes with some ligands, it is feasible to design mutants by replacing residues in the binding sites with the aim of synthesising proteins with better selectivity and improved physical properties, as demonstrated in a number of cases.

Identification, Expression Patterns, and Functional Characterization of Chemosensory Proteins in Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae)

The Chinese white pine beetle, Dendroctonus armandi Tsai and Li (Coleoptera: Curculionidae: Scolytinae), is a serious pest of coniferous forests in China. Thus, there is considerable interest in developing eco-friendly pest-control methods, with the use of semiochemicals as a distinct possibility. Olfaction is extremely important for fitness of D. armandi because it is the primary mechanism through which the insect locates hosts and mates. Thus, here we characterized nine full-length genes encoding chemosensory proteins (CSPs) from D. armandi. The genes were ubiquitously and multiply expressed across different developmental stages and adult tissues, indicating various roles in developmental metamorphosis, olfaction, and gustation. Ligand-binding assays implied that DarmCSP2 may be the carrier of D. armandi pheromones and various plant host volatiles. These volatiles were identified through RNA interference of DarmCSP2 as: (+)-α-pinene, (+)-β-pinene, (−)-β-pinene, (+)-camphene, (+)-3-carene, and myrcene. The systematic chemosensory functional analysis of DarmCSP2 in this study clarified the molecular mechanisms underlying D. armandi olfaction and provided a theoretical foundation for eco-friendly pest control.

Transcriptome analysis in different developmental stages of Batocera horsfieldi (Coleoptera: Cerambycidae) and comparison of candidate olfactory genes

The white-striped longhorn beetle Batocera horsfieldi (Coleoptera: Cerambycidae) is a polyphagous wood-boring pest that causes substantial damage to the lumber industry. Moreover olfactory proteins are crucial components to function in related processes, but the B. horsfieldi genome is not readily available for olfactory proteins analysis. In the present study, developmental transcriptomes of larvae from the first instar to the prepupal stage, pupae, and adults (females and males) from emergence to mating were built by RNA sequencing to establish a genetic background that may help understand olfactory genes. Approximately 199 million clean reads were obtained and assembled into 171,664 transcripts, which were classified into 23,380, 26,511, 22,393, 30,270, and 87, 732 unigenes for larvae, pupae, females, males, and combined datasets, respectively. The unigenes were annotated against NCBI’s non-redundant nucleotide and protein sequences, Swiss-Prot, Gene Ontology (GO), Pfam, Clusters of Eukaryotic Orthologous Groups (KOG), and KEGG Orthology (KO) databases. A total of 43,197 unigenes were annotated into 55 sub-categories under the three main GO categories; 25,237 unigenes were classified into 26 functional KOG categories, and 25,814 unigenes were classified into five functional KEGG Pathway categories. RSEM software identified 2,983, 3,097, 870, 2,437, 5,161, and 2,882 genes that were differentially expressed between larvae and males, larvae and pupae, larvae and females, males and females, males and pupae, and females and pupae, respectively. Among them, genes encoding seven candidate odorant binding proteins (OBPs) and three chemosensory proteins (CSPs) were identified. RT-PCR and RT-qPCR analyses showed that BhorOBP3, BhorCSP2, and BhorOBPC1/C3/C4 were highly expressed in the antenna of males, indicating these genes may may play key roles in foraging and host-orientation in B. horsfieldi. Our results provide valuable molecular information about the olfactory system in B. horsfieldi and will help guide future functional studies on olfactory genes.

De Novo Transcriptome Analysis of the Common New Zealand Stick Insect Clitarchus hookeri (Phasmatodea) Reveals Genes Involved in Olfaction, Digestion and Sexual Reproduction

Phasmatodea, more commonly known as stick insects, have been poorly studied at the molecular level for several key traits, such as components of the sensory system and regulators of reproduction and development, impeding a deeper understanding of their functional biology. Here, we employ de novo transcriptome analysis to identify genes with primary functions related to female odour reception, digestion, and male sexual traits in the New Zealand common stick insect Clitarchus hookeri (White). The female olfactory gene repertoire revealed ten odorant binding proteins with three recently duplicated, 12 chemosensory proteins, 16 odorant receptors, and 17 ionotropic receptors. The majority of these olfactory genes were over-expressed in female antennae and have the inferred function of odorant reception. Others that were predominantly expressed in male terminalia (n = 3) and female midgut (n = 1) suggest they have a role in sexual reproduction and digestion, respectively. Over-represented transcripts in the midgut were enriched with digestive enzyme gene families. Clitarchus hookeri is likely to harbour nine members of an endogenous cellulase family (glycoside hydrolase family 9), two of which appear to be specific to the C. hookeri lineage. All of these cellulase sequences fall into four main phasmid clades and show gene duplication events occurred early in the diversification of Phasmatodea. In addition, C. hookeri genome is likely to express γ-proteobacteria pectinase transcripts that have recently been shown to be the result of horizontal transfer. We also predicted 711 male terminalia-enriched transcripts that are candidate accessory gland proteins, 28 of which were annotated to have molecular functions of peptidase activity and peptidase inhibitor activity, two groups being widely reported to regulate female reproduction through proteolytic cascades. Our study has yielded new insights into the genetic basis of odour detection, nutrient digestion, and male sexual traits in stick insects. The C. hookeri reference transcriptome, together with identified gene families, provides a comprehensive resource for studying the evolution of sensory perception, digestive systems, and reproductive success in phasmids.

Cloning, expression and localization of DacaCSP2 and DacaCSP3 during different reproductive stages in Daphnia carinata

Daphnia carinata are unique freshwater crustaceans that undergo both sexual and asexual reproduction, depending on environmental factors. While the molecular mechanism behind the reproductive transformation has been unknown, chemosensory proteins (CSPs) may be involved. We have cloned the cDNA sequences of two CSP genes from D. carinata using primers based on homologous sequences and rapid amplification of cDNA ends (RACE). The full-length cDNA of DacaCSP2 (GenBank accession no: KM624608) was 632 bp, with an ORF (open reading frame) of 330 bp encoding a 12.02 kDa protein; and the full-length cDNA of DacaCSP3 (GenBank accession no: KM624609) was 935 bp, with an ORF of 342 bp encoding a 12.78kDa protein. Both CSPs encoded an N-terminal signal peptide, four conserved cysteines, an OS-D superfamily domain, a 2Fe-2S ferredoxin domain, an anaphylatoxin domain and an EGF-like domain. DaCaCSP2 and DaCaCSP3 proteins were most closely related to CSPs from Daphnia pulex and were more distantly related to CSPs from other insects. Using quantitative PCR, we found expression levels of DaCaCSP2 and DaCaCSP3 mRNA were highest in sexual females, followed by parthenogenetic females, and lowest in males. The expression levels of DaCaCSP2 and DaCaCSP3 mRNA also increased at lower temperatures, which suggested they could respond to environmental cues. Whole mount in situ hybridization (ISH) showed that DaCaCSP2 and DaCaCSP3 were expressed mainly in the ovaries, summer eggs, thoracic limbs, rectum and second antennae in sexual females; while they were expressed mainly in the ovaries, thoracic limbs, rectum and second antennae in parthenogenetic females. Together, these results suggest that DacaCSP2 and DacaCSP3 may respond to environmental cues and control the reproductive switch from sexual to asexual reproduction in D. carinata.

Si-CSP9 regulates the integument and moulting process of larvae in the red imported fire ant, Solenopsis invicta

Chemosensory proteins (CSPs) have been predicted to be involved in development; however, direct evidence for their involvement is lacking, and genetic basis is largely unknown. To determine the function of the chemosensory protein 9 (Si-CSP9) gene in Solenopsis invicta, we used RNA interference to silence Si-CSP9 in 3rd-instar larvae. The 3rd-instar larvae failed to shed their cuticle after being fed Si-CSP9-directed siRNA, and expression profiling of RNAi-treated and untreated control larvae showed that 375 genes were differentially expressed. Pathway enrichment analysis revealed that 4 pathways associated with larval development were significantly enriched. Blast analysis revealed that one fatty acid amide hydrolase (FAAH) gene was up-regulated and 4 fatty acid synthase (FAT) genes and one protein kinase DC2 gene (PKA) were down-regulated in the enriched pathways. Significantly higher expression of these genes was found in 4th-instar larvae, and Pearson correlation analysis of the expression patterns revealed significant relationships among Si-CSP9, PKA, FAAH, and FAT1-4. Moreover, we confirmed that expression levels of Si-CSP9, FAAH, and FAT1-4 were significantly reduced and that the development of 3rd-instar larvae was halted with PKA silencing. These results suggest that Si-CSP9 and PKA may be involved in the network that contributes to development of 3rd-instar larvae.

Identification, expression profiling and fluorescence-based binding assays of a chemosensory protein gene from the Western flower thrips, Frankliniella occidentalis

Using RT-PCR and RACE-PCR strategies, we cloned and identified a new chemosensory protein (FoccCSP) from the Western flower thrips, Frankliniella occidentalis, a species for which no chemosensory protein (CSP) has yet been identified. The FoccCSP gene contains a 387 bp open-reading frame encoding a putative protein of 128 amino acids with a molecular weight of 14.51 kDa and an isoelectric point of 5.41. The deduced amino acid sequence contains a putative signal peptide of 19 amino acid residues at the N-terminus, as well as the typical four-cysteine signature found in other insect CSPs. As FoccCSP is from a different order of insect than other known CSPs, the GenBank FoccCSP homolog showed only 31-50% sequence identity with them. A neighbor-joining tree was constructed and revealed that FoccCSP is in a group with CSPs from Homopteran insects (e.g., AgosCSP4, AgosCSP10, ApisCSP, and NlugCSP9), suggesting that these genes likely developed from a common ancestral gene. The FoccCSP gene expression profile of different tissues and development stages was measured by quantitative real-time PCR. The results of this analysis revealed this gene is predominantly expressed in the antennae and also highly expressed in the first instar nymph, suggesting a function for FoccCSP in olfactory reception and in particular life activities during the first instar nymph stage. We expressed recombinant FoccCSP protein in a prokaryotic expression system and purified FoccCSP protein by affinity chromatography using a Ni-NTA-Sepharose column. Using N-phenyl-1-naphthylamine (1-NPN) as a fluorescent probe in fluorescence-based competitive binding assay, we determined the binding affinities of 19 volatile substances for FoccCSP protein. This analysis revealed that anisic aldehyde, geraniol and methyl salicylate have high binding affinities for FoccCSP, with KD values of 10.50, 15.35 and 35.24 μM, respectively. Thus, our study indicates that FoccCSP may play an important role in regulating the development of the first instar nymph and mediate F. occidentalis host recognition.

Odorant-binding proteins and olfactory coding in the solitary bee Osmia cornuta

Solitary bees are major pollinators but their chemical communication system has been poorly studied. We investigated olfactory coding in Osmia cornuta from two perspectives, chemical and biochemical. We identified (E)-geranyl acetone and 2-hexyl-1,3-dioxolane, specifically secreted by females and males, respectively. A transcriptome analysis of antennae revealed 48 ORs (olfactory receptors), six OBPs (odorant-binding proteins), five CSPs (chemosensory proteins), and a single SNMP (sensory neuron membrane protein). The numbers of ORs and OBPs are much lower than in the honeybee, in particular, C-minus OBPs are lacking in the antennae of O. cornuta. We have expressed all six OBPs of O. cornuta and studied their binding specificities. The best ligands are common terpene plant odorants and both volatiles produced by the bee and identified in this work.

Expression analysis and binding experiments of chemosensory proteins indicate multiple roles in Bombyx mori

Chemosensory proteins (CSPs) are a family of small soluble proteins that, in addition to the odorant-binding proteins (OBPs), are involved in chemical communication. To understand the physiological function of the 16 known CSPs in the silkworm Bombyx mori, we investigated the expression patterns in different tissues and developmental stages using quantitative real-time RT-PCR (Q-PCR) and Western blot analysis. The results indicated that most CSPs were widely expressed in embryos, larvae, pupae and adults but were developmentally regulated. Such broad spatial and temporal expression was inconsistent with a specific association with chemosensory function. We conclude that CSPs are multifunctional proteins that are involved in diverse cellular processes and that can play non-chemosensory as well as chemosensory roles. Binding experiments revealed different binding characteristics of CSP1 and CSP2, with retinal being the best ligand, suggesting a putative function of these CSPs as carriers.

Molecular cloning, expression and molecular modeling of chemosensory protein from Spodoptera litura and its binding properties with Rhodojaponin III

Insects stimulate specific behaviors by the correct recognition of the chemicals in the external environment. Rhodojaponin III is a botanical grayanoid diterpenid oviposition deterrent isolated from Rhododendron molle. In this study we aimed to determine whether the CSPs involved in the recognition of Rhodojaponin III. A full-length cDNA encoding chemosensory protein was isolated from the antennae of Spodoptera litura Fabricius (CSPSlit, GenBank Accession No. DQ007458). The full-length cDNA of NlFoxA is 1789 bp and has an open reading frame (ORF) of 473 bp, encoding a protein of 126 amino acids, Northern blot analysis revealed that CSPSlit mRNA was mainly expressed in the antennae, legs, wings and female abdomens. A three-dimensional model of CSPSlit was constructed using homology modeling method, and its reliability was evaluated. The active site of CSPSlit was calculated using CDOCKER program indicated that the Tyr24, Ile45, Leu49, Thr64, Leu68, Trp79 and Leu82 were responsible ligand-binding active site on identifying Rhodojaponin III in the CSPSlit. The recombinant CSPSlit protein was expressed in Escherichia coli and purified using single-step Ni-NTA affinity chromatography. Fluorescence emission spectra revealed that the CSPSlit protein had significant affinity to rhodojaponin III. These results mean that CSPSlit is critical for insects identify the Rhodojaponin III.

Ultrastructural characterization of olfactory sensilla and immunolocalization of odorant binding and chemosensory proteins from an ectoparasitoid Scleroderma guani (Hymenoptera: Bethylidae)

The three-dimensional structures of two odorant binding proteins (OBPs) and one chemosensory protein (CSP) from a polyphagous ectoparasitoid Scleroderma guani (Hymenoptera: Bethylidae) were resolved bioinformatically. The results show that both SguaOBP1 and OBP2 are classic OBPs, whereas SguaCSP1 belongs to non-classic CSPs which are considered as the “Plus-C” CSP in this report. The structural differences between the two OBPs and between OBP and CSP are thoroughly described, and the structural and functional significance of the divergent C-terminal regions (e.g., the prolonged C-terminal region in SguaOBP2 and the additional pair of cysteines in SguaCSP1) are discussed. The immunoblot analyses with antisera raised against recombinant SguaOBP1, OBP2, and CSP1, respectively, indicate that two SguaOBPs are specific to antennae, whereas SguaCSP1, which are more abundant than OBPs and detected in both male and female wasps, expresses ubiquitously across different tissues.

We also describe the ultrastructure of the antennal sensilla types in S. guani and compare them to 19 species of parasitic Hymenoptera. There are 11 types of sensilla in the flagellum and pedicel segments of antennae in both male and female wasps. Seven of them, including sensilla placodea (SP), long sensilla basiconica (LSB), sensilla coeloconica (SC), two types of double-walled wall pore sensilla (DWPS-I and DWPS-II), and two types of sensilla trichodea (ST-I and ST-II), are multiporous chemosensilla. The ultralsturctures of these sensilla are morphologically characterized. In comparison to monophagous specialists, the highly polyphagous generalist ectoparasitoids such as S. guani possess more diverse sensilla types which are likely related to their broad host ranges and complex life styles. Our immunocytochemistry study demonstrated that each of the seven sensilla immunoreacts with at least one antiserum against SguaOBP1, OBP2, and CSP1, respectively. Anti-OBP2 is specifically labeled in DWPS-II, whereas the anti-OBP1 shows a broad spectrum of immunoactivity toward four different sensilla (LSB, SP, ST-I and ST-II). On the other hand, anti-CSP1 is immunoactive toward SP, DWPS-I and SC. Interestingly, a cross co-localization pattern between SguaOBP1 and CSP1 is documented for the first time. Given that the numbers of OBPs and CSPs in many insect species greatly outnumber their antennal sensilla types, it is germane to suggest such phenomenon could be the rule rather than the exception.

Screening of T7 phage displayed Bactrocera dorsalis (Hendel) antenna cDNA library against chemosensory protein

Recent studies have shown that chemosensory proteins (CSPs) were involved in diverse life activities such as insect feeding, development, mating, immune regulation, as well as other important circadian rhythms, etc. To screen the proteins involved in the BdorCSP-related physiological activity, a cDNA library of the Bactrocera dorsalis (Hendel) antenna expressed on the surface of T7 phage was screened against BdorCSP. After four rounds of screening, ELISA-positive samples of selected phages were sequenced and identified as protein disulfide isomerase (PDI), trypsin-like serine protease (Ser), TakeOut (TO), and a new protein by GenBank blast, respectively. Real-time quantitative PCR results showed that the expression levels of Ser, TO, and the new protein were the highest in antenna, sharing similar expression pattern with BdorCSP. These results reveal that these proteins might be involved in the BdorCSP-related physiological or metabolic activities. This work paves a new way for exploring the function of CSPs.

Identification and molecular cloning of putative odorant-binding proteins and chemosensory protein from the bethylid wasp, Scleroderma guani Xiao et Wu

Two putative odorant-binding proteins (OBPs) and one putative chemosensory protein (CSP) from females of the ant-like bethylid wasp, Scleroderma guani Xiao et Wu (Hymenoptera: Bethylidae), were identified and cloned. The putative OBPs and CSP were identified by nondenaturing polyacrylamide gel electrophoresis (native-PAGE). 3' rapid amplification of cDNA ends (3'RACE) was performed to obtain the sequences of the mature proteins by using degenerate primers designed from N-terminal sequences. Gene-specific primers for 5' rapid amplification of cDNA ends (5'RACE) were designed according to 3'RACE results and used in polymerase chain reaction (PCR) to obtain full-length sequences. The proteins (Sgua-OBP1, Sgua-OBP2, and Sgua-CSP1) encode 133, 142, and 129 amino acid-deduced sequences, respectively. Prediction of signal peptide sequences matches the N-terminal amino acid sequence of the isolated proteins. Database searches suggest that the Sgua-OBP1 and Sgua-OBP2 are homologs of OBPs from other insects, and Sgua-CSP1 shares a high level of identity with previously described CSPs.

Identification and expression pattern of the chemosensory protein gene family in the silkworm, Bombyx mori

Insect chemosensory proteins (CSPs) as well as odorant-binding proteins (OBPs) have been supposed to transport hydrophobic chemicals to receptors on sensory neurons. Compared with OBPs, CSPs are expressed more broadly in various insect tissues. We performed a genome-wide analysis of the candidate CSP gene family in the silkworm. A total of 20 candidate CSPs, including 3 gene fragments and 2 pseudogenes, were characterized based on their conserved cysteine residues and their similarity to CSPs in other insects. Some of these genes were clustered in the silkworm genome. The gene expression pattern of these candidates was investigated using RT-PCR and microarray, and the results showed that these genes were expressed primarily in mature larvae and the adult moth, suggesting silkworm CSPs may be involved in development. The majority of silkworm CSP genes are expressed broadly in tissues including the antennae, head, thorax, legs, wings, epithelium, testes, ovaries, pheromone glands, wing disks, and compound eyes.

RNAi-induced phenotypes suggest a novel role for a chemosensory protein CSP5 in the development of embryonic integument in the honeybee (Apis mellifera)

Small chemosensory proteins (CSPs) belong to a conserved, but poorly understood, protein family found in insects and other arthropods. They exhibit both broad and restricted expression patterns during development. In this paper, we used a combination of genome annotation, transcriptional profiling and RNA interference to unravel the functional significance of a honeybee gene (csp5) belonging to the CSP family. We show that csp5 expression resembles the maternal-zygotic pattern that is characterized by the initiation of transcription in the ovary and the replacement of maternal mRNA with embryonic mRNA. Blocking the embryonic expression of csp5 with double-stranded RNA causes abnormalities in all body parts where csp5 is highly expressed. The treated embryos show a "diffuse", often grotesque morphology, and the head skeleton appears to be severely affected. They are 'unable-to-hatch' and cannot progress to the larval stages. Our findings reveal a novel, essential role for this gene family and suggest that csp5 (unable-to-hatch) is an ectodermal gene involved in embryonic integument formation. Our study confirms the utility of an RNAi approach to functional characterization of novel developmental genes uncovered by the honeybee genome project and provides a starting point for further studies on embryonic integument formation in this insect.

A microarray approach identifies ANT, OS-D and takeout-like genes as differentially regulated in alate and apterous morphs of the green peach aphid Myzus persicae (Sulzer)

Aphids exhibit a complex life cycle in which their phenotypes vary in response to environmental changes. Wing polyphenism is one of the phenotypes that have not been adequately studied. We developed a cDNA microarray from the green peach aphid Myzus persicae (Sulzer), and compared mRNA samples derived from alate and apterous adults. The microarray experiment resulted in 108 significantly changing clones that represented 31 unique ESTs. Among the highest and significantly expressed clones in alate adults, seven clones showed portions of a new adenine nucleotide translocase (ANT) gene from M. persicae and four clones contained sequences of the OS-D gene. Another clone showed significant homology with the takeout (TO) and TO-like proteins described from other insects. A full-length cDNA clone of M. persicae ANT (Mp ANT) was isolated and characterized. An reverse transcription-polymerase chain reaction (RT-PCR) analysis showed significant differences in Mp ANT, OS-D and Mp takeout-like genes (Mp TOL) expression in alate compared to apterous adults. A polyclonal antibody against the beef heart mitochondrial ANT reacted with a recombinant Mp ANT expressed in Escherichia coli, as it did with aphid extracts, showing higher amounts of the expected 33kDa band in alate adults. Spatial expression analysis showed higher Mp ANT expression in the thorax compared to head, abdomen, leg and antennae. OS-D and Mp TOL showed ubiquitous expression across the body, with OS-D being significantly higher in legs and antennae while Mp TOL being significantly higher in the head and abdomen. The possible causes for higher expression of ANT, OS-D and TOL in alates and the physiological effects on the aphid flight and dispersal are discussed.

Developmental expression patterns of four chemosensory protein genes from the Eastern spruce budworm, Chroistoneura fumiferana

Chemosensory proteins (CSPs) are associated with insect sensory organs, including the sensillum lymph in some cases. However, they are also commonly expressed in nonsensory tissues that lack gustatory and olfactory neurones. We characterized the sex and development specific expression patterns of four CSP genes from the Eastern spruce budworm (ESB) using Northern blots. CfumAY426540.2 was detected at high levels in adult moths. Conversely, CfumAY426538 was expressed in all stages except adult moths, and was most abundant during late stages of the 6th instar. CfumAY701858 was expressed in all stages, while CfumAY426539 was detected less frequently, at specific developmental stages such as the 5th to 6th instar moult. During a natural moult, and a premature moult induced by the ecdysteroid agonist tebufenozide, CfumAY701858 and CfumAY426539 were up-regulated, while CfumAY426538 appeared to be down-regulated. Our results suggest that some members of the CSP gene family from the ESB may be involved in development, including moulting.

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.

Analysis of the insect os-d-like gene family

Insect OS-D-like proteins, also known as chemosensory (CSP) or sensory appendage proteins (SAP), are broadly expressed in various insect tissues, where they are thought to bind short to medium chain length fatty acids and their derivatives. Although their specific function remains uncertain, OS-D-like members have been isolated from sensory organs (including the sensillum lymph in some cases), and a role in olfaction similar to that of the insect odorant binding proteins (OBP) has been suggested for some. We have identified 15 new OS-D-like sequences: four from cDNA clones described herein and 11 from sequence databases. The os-d-like genes from the Anopheles gambiae, Apis mellifera, Drosophila melanogaster, and Drosophila pseudoobscura genomes typically have single, small introns with a conserved splice site. Together with all family members entered on GenBank, a total of 70 OS-D-like proteins, representing the insect orders Diptera, Dictyoptera, Hymenoptera, Lepidoptera, Orthoptera, and Phasmatodea, were analyzed. A neighbor joining distance phenogram identified several protein similarity classes that were characterized by highly conserved sequence motifs, including (A) N-terminal YTTKYDN(V/I)(N/D)(L/V)DEIL, (B) central DGKELKXX(I/L)PDAL, and (C) C-terminal KYDP. In contrast, three similarity classes were characterized by their diversion from these conserved motifs. The functional importance of conserved amino acid residues is discussed in relation to the crystal and NMR structures of MbraCSPA6.

Bioinformatics-based identification of chemosensory proteins in African Malaria Mosquito, Anopheles gambiae

Chemosensory proteins (CSPs) are identifiable by four spatially conserved Cysteine residues in their primary structure or by two disulfide bridges in their tertiary structure according to the previously identified olfactory specific-D related proteins. A genomics- and bioinformatics-based approach is taken in the present study to identify the putative CSPs in the malaria-carrying mosquito, Anopheles gambiae. The results show that five out of the nine annotated candidates are the most possible Anopheles CSPs of A. gambiae. This study lays the foundation for further functional identification of Anopheles CSPs, though all of these candidates need additional experimental verification.

Moth chemosensory protein exhibits drastic conformational changes and cooperativity on ligand binding

Chemosensory proteins (CSPs) have been proposed to transport hydrophobic chemicals from air to olfactory or taste receptors. They have been isolated from several sensory organs of a wide range of insect species. The x-ray structure of CSPMbraA6, a 112-aa antennal protein from the moth Mamestra brassicae (Mbra), was shown to exhibit a novel type of alpha-helical fold. We have performed a structural and binding study of CSPMbraA6 to get some insights into its possible molecular function. Tryptophan fluorescence quenching demonstrates the ability of CSPMbraA6 to bind several types of semio-chemicals or surrogate ligands with microM K(d). Its crystal structure in complex with one of these compounds, 12-bromo-dodecanol, reveals extensive conformational changes on binding, resulting in the formation of a large cavity filled by three ligand molecules. Furthermore, binding cooperativity was demonstrated for some ligands, suggesting a stepwise binding. The peculiar rearrangement of CSPMbraA6 conformation and the cooperativity phenomenon might trigger the recognition of chemicals by receptors and induce subsequent signal transduction.

Chemosensory proteins of Locusta migratoria

Two different classes of chemosensory proteins (CSPs) in Locusta migratoria have been identified on the basis of the molecular cloning of a series of different cDNAs from the antennae of this insect. Several CSP isoforms have been purified and biochemically characterized from antennal and wing extracts, some of them corresponding to expression products predicted for the identified cDNAs. In wings, the nature of the main endogenous ligand binding to these proteins was determined as oleoamide by a gas chromatography-mass spectrometric approach. One of these isoforms has been expressed in a bacterial system with high yield and used in a fluorescent binding assay. Competitive binding experiments have indicated the presence of long-chain compounds among the best ligands.

Solution structure of a chemosensory protein from the moth Mamestra brassicae

Chemosensory proteins (CSPs) are believed to be involved in chemical communication and perception. A number of such proteins, of molecular mass approximately 13 kDa, have been isolated from different sensory organs of a wide range of insect species. Several CSPs have been identified in the antennae and proboscis of the moth Mamestra brassicae. CSPMbraA6, a 112-amino-acid antennal protein, has been expressed in a soluble form in large quantities in the Escherichi coli periplasm. NMR structure determination of CSPMbraA6 has been performed with 1H- and 15N-labelled samples. The calculated structures present an average root mean square deviation about the mean structure of 0.63 A for backbone atoms and 1.27 A for all non-hydrogen atoms except the 12 N-terminal residues. The protein is well folded from residue 12 to residue 110, and consists of a non-bundle alpha-helical structure with six helices connected by alpha alpha loops. It has a globular shape, with overall dimensions of 32 A x 28 A x 24 A. A channel is visible in the hydrophobic core, with dimensions of 3 A x 9 A x 21 A. In some of the 20 solution structures calculated, this channel is closed either by Trp-94 at one end or by Tyr-26 at the other end; in some other solutions, this channel is closed at both ends. Binding experiments with 12-bromododecanol indicate that the CSPMbraA6 structure is modified upon ligand binding.

Characterization of a chemosensory protein (ASP3c) from honeybee (Apis mellifera L.) as a brood pheromone carrier

Chemosensory proteins (CSPs) are ubiquitous soluble small proteins isolated from sensory organs of a wide range of insect species, which are believed to be involved in chemical communication. We report the cloning of a honeybee CSP gene called ASP3c, as well as the structural and functional characterization of the encoded protein. The protein was heterologously secreted by the yeast Pichia pastoris using the native signal peptide. ASP3c disulfide bonds were assigned after trypsinolysis followed by chromatography and mass spectrometry combined with microsequencing. The pairing (Cys(I)-Cys(II), Cys(III)-Cys(IV)) was found to be identical to that of Schistocerca gregaria CSPs, suggesting that this pattern occurs commonly throughout the insect CSPs. CD measurements revealed that ASP3c mainly consists of alpha-helices, like other insect CSPs. Gel filtration analysis showed that ASP3c is monomeric at neutral pH. Using ASA, a fluorescent fatty acid anthroyloxy analogue as a probe, ASP3c was shown to bind specifically to large fatty acids and ester derivatives, which are brood pheromone components, in the micromolar range. It was unable to bind tested general odorants and other tested pheromones (sexual and nonsexual). This is the first report on a natural pheromonal ligand bound by a recombinant CSP with a measured affinity constant.

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.

X-ray structure and ligand binding study of a moth chemosensory protein

Chemosensory proteins (CSPs) are believed to be involved in chemical communication and perception. Such proteins, of M(r) 13,000, have been isolated from several sensory organs of a wide range of insect species. Several CSPs have been identified in the antennae and proboscis of the moth Mamestra brassicae. One of them, CSPMbraA6, a 112-amino acid antennal protein, has been expressed in large quantities and is soluble in the Escherichia coli periplasm. X-ray structure determination has been performed in parallel with ligand binding assays using tryptophan fluorescence quenching. The protein has overall dimensions of 25 x 30 x 32 A and exhibits a novel type of alpha-helical fold with six helices connected by alpha-alpha loops. A narrow channel extends within the protein hydrophobic core. Fluorescence quenching with brominated alkyl alcohols or fatty acids and modeling studies indicates that CSPMbraA6 is able to bind such compounds with C12-18 alkyl chains. These ubiquitous proteins might have the role of extracting hydrophobic linear compounds (pheromones, odors, or fatty acids) dispersed in the phospholipid membrane and transporting them to their receptor.

Binding properties of a locust's chemosensory protein

The chemosensory protein CSP-sg4 of the desert locust Schistocerca gregaria binds reversibly N-phenyl-1-naphthylamine in fluorescent-binding assays, with a dissociation constant of 4 microM. Upon binding to the protein, the emission peaks of the fluorescent probe undergo a marked blue shift, accompanied by an order of magnitude increase of the maximum intensity. The assay has also allowed the measurement of the affinity of CSP to other aromatic and aliphatic compounds. The binding capacity of this protein is unaffected by thermal treatments up to 100 degrees C for 20 min. The ligand-binding characteristics of chemosensory proteins may help in clarifying the role of this recently discovered class of soluble proteins in chemoreception.

Ultrastructural characterization of antennal sensilla and immunocytochemical localization of a chemosensory protein in Carausius morosus Brünner (Phasmida: Phasmatidae)

The aim of this work was to investigate the olfactory system of the walking stick insect, Carausius morosus. Morphological, ultrastructural and immunocytochemical studies of adult female antennae were conducted by scanning and transmission electron microscopy. Extensive cross-section series were made through the last antennal segment to define the cuticular apparatus, wall pore distribution and the number of innervating receptor neurons of each sensillum type. Single-walled wall pore sensilla occur in three subtypes: (i) with 27 or 28 branched receptor neurons, (ii) with two branched neurons and (iii) with one or two unbranched neurons, respectively. Double-walled wall pore sensilla were found in two subtypes with spoke channels, one with four unbranched neurons, the other with two unbranched neurons. One terminal pore sensillum was found, showing two cavities within the hair and being innervated by six sensory cells. Immunocytochemical experiments were performed to show the localization of a 19 kDa soluble protein found in the chemosensory organs of C. morosus. This protein shows an amino acid sequence homologous to the family of chemosensory proteins (CSP). The polyclonal antibody raised against the purified protein (CSP-cmA) showed, for the first time in CSPs, a strong labeling in olfactory sensilla, specifically in the sensillum lymph surrounding the dendritic branches of SW-WP sensilla and in the uninnervated lumen between the two concentric walls of DW-WP type 1 sensilla.

Identity and expression pattern of chemosensory proteins in Heliothis virescens (Lepidoptera, Noctuidae)

Analyzing the chemosensory organs of the moth Heliothis virescens, three proteins belonging to the family of insect chemosensory proteins (CSPs) have been cloned; they are called HvirCSP1, HvirCSP2 and HvirCSP3. The HvirCSPs show about 50% identity between each other and 30-76% identity to CSPs from other species. Overall, they are rather hydrophilic proteins but include a conserved hydrophobic motif. Tissue distribution and temporal expression pattern during the last pupal stages were assessed by Northern blots. HvirCSP mRNAs were detected in various parts of the adult body with a particular high expression level in legs. The expression of HvirCSP1 in legs started early during adult development, in parallel with the appearance of the cuticle. HvirCSP1 mRNA was detectable five days before eclosion (day E-5), increased dramatically on day E-3 and remained at high level into adult life. The tissue distribution and the time course of appearance of HvirCSPs are in agreement with a possible role in contact chemosensation.

Chemosensory protein from the moth Mamestra brassicae. Expression and secondary structure from 1H and 15N NMR

A group of ubiquitous small proteins (average 13 kDa) has been isolated from several sensory organs of a wide range of insect species. They are believed to be involved in chemical communication and perception (olfaction or taste) and have therefore been called chemo-sensory proteins (CSPs). Several CSPs have been identified in the antennae and proboscis of the moth Mamestra brassicae. We have expressed one of the antennal proteins (CSPMbraA6) in large quantities as a soluble recombinant protein in Escherichia coli periplasm. This 112-residue protein is a highly soluble monomer of 13 072 Da with a pI of 5.5. NMR data (1H and 15N) indicate that CSPMbraA6 is well folded and contains seven alpha helices (59 amino acids) and two short extended structures (12 amino acids) from positions 5 to 10 and from 107 to 112. Thirty-seven amino acids are involved in beta turns and coiled segments and four amino acids are not assigned in the NMR spectra (the N-terminus and the residue 52 in the loop 48-53), probably due to their mobility. This is the first report on the expression and structural characterization of a recombinant CSP.

Bacterial expression and conformational analysis of a chemosensory protein from Schistocerca gregaria

Chemosensory proteins (CSPs) are a class of small, soluble proteins present at high concentrations in chemosensory organs of different insect species. Several pieces of evidence suggest their involvement in carrying chemical messages from the environment to chemosensory receptors. However, a structural description of the mechanism of delivery has not been reported. In order to provide the first detailed conformational characterization of these molecules, we cloned a specific isoform (CSP-sg4) from Schistocerca gregaria and expressed it in Escherichia coli. The product was obtained with yields of more than 20 mg per L of culture, all in its soluble form. The recombinant protein was identical to the native one with respect to pairing of the disulfide bridges, aggregative state and secondary structure elements. Structural investigations revealed a significantly stable polypeptide with respect to variations in temperature and acidity. CD analysis, preliminary NMR data and secondary structure prediction pointed to a correctly folded structure where helical regions and loops are alternated in a similar fashion as that observed for other classes of odorant- and pheromone-binding proteins presenting no sequence similarity to CSPs.