Discovery of a linear lead antagonist to the insect pheromone biosynthesis activating neuropeptide (PBAN)

Identification of mature peptides from pban and capa genes of the moths Heliothis peltigera and Spodoptera littoralis

By transcriptome analysis, we identified PBAN and CAPA precursors in the moths Spodoptera littoralis and Heliothis peltigera which are among the most damaging pests of agriculture in tropical and subtropical Africa as well as in Mediterranean countries. A combination of mass spectrometry and immunocytochemistry was used to identify mature peptides processed from these precursors and to reveal their spatial distribution in the CNS. We found that the sites of expression of pban genes, the structure of PBAN precursors and the processed neuropeptides are very similar in noctuid moths. The sequence of the diapause hormone (DH; tryptopyrokinin following the signal peptide), however, contains two N-terminal amino acids more than expected from comparison with already published sequences of related species. Capa genes of S. littoralis and H. peltigera encode, in addition to periviscerokinins, a tryptopyrokinin showing sequence similarity with DH, which is the tryptopyrokinin of the pban gene. CAPA peptides, which were not known from any noctuid moth so far, are produced in cells of abdominal ganglia. The shape of the release sites of these hormones in H. peltigera represents an exceptionally derived trait state and does not resemble the well-structured abdominal perisympathetic organs which are known from many other insects. Instead, axons of CAPA cells extensively ramify within the ventral diaphragm. The novel information regarding the sequences of all mature peptides derived from pban and capa genes of H. peltigera and S. littoralis now enables a detailed analysis of the bioactivity and species-specificity of the native peptides, especially those from the hitherto unknown capa genes, and to explore their interactions with PBAN/DH receptors.

Pheromonotropic and melanotropic PK/PBAN receptors: differential ligand-receptor interactions

The aim of the present study was to further characterize the PK/PBAN receptors and their interaction with various PK/PBAN peptides in order to get a better understanding of their ubiquitous and multifunctional nature. Two cloned receptors stably expressed in Spodoptera frugiperda (Sf9) cells were used in this study: a Heliothis peltigera pheromone gland receptor (Hep-PK/PBAN-R) (which stimulates sex pheromone biosynthesis) and Spodoptera littoralis larval receptor (Spl-PK/PBAN-R) (which mediates cuticular melanization in moth larvae) and their ability to respond to several native PK/PBAN peptides: β-subesophageal neuropeptide (β-SGNP), myotropin (MT) and Leucophaea maderae pyrokinin (LPK), as well as linear and cyclic analogs was tested by monitoring their ability to stimulate Ca(2+) release. The receptors exhibited a differential response to β-SGNP, which activated the Hep-PK/PBAN-R but not the Spl-PK/PBAN-R - a response opposite to that previously demonstrated with diapause hormone (DH). MT was somewhat more active on Spl-PK/PBAN-R than on Hep-PK/PBAN-R. LPK elicited similar positive responses in both receptors (like that with PBAN). A differential response toward both receptors was also noticed with the PBAN-derived backbone cyclic (BBC) conformationally constrained peptide BBC-5. The peptides BBC-7 and BBC-8 activated both receptors. The results correlate between two PK/PBAN mediated function (cuticular melanization and sex pheromone biosynthesis) and the peptides that activate them and thus advance our understanding of the mode of action of the PK/PBAN family, and might help in exploring novel high-affinity receptor-specific antagonists that could serve as a basis for development of new families of insect-control agents.

Structural and functional differences between pheromonotropic and melanotropic PK/PBAN receptors

BACKGROUND

The pyrokinin/pheromone biosynthesis-activating neuropeptide (PK/PBAN) plays a major role in regulating a wide range of physiological processes in insects. The ubiquitous and multifunctional nature of the PK/PBAN peptide family raises many questions regarding the mechanisms by which these neuropeptides elicit their effects and the nature of the receptors that mediate their functions.

METHODS

A sex pheromone gland receptor of the PK/PBAN family from Heliothis peltigera female moth and a Spodoptera littoralis larval receptor were cloned and stably expressed, and their structural models, electrostatic potentials and cellular functional properties were evaluated.

RESULTS

Homology modeling indicated highly conserved amino-acid residues in appropriate structural positions as experimentally shown for class A G-protein coupled receptors. Structural differences could be proposed and electrostatic potentials of the two receptor models revealed net charge differences. Calcium mobilization assays demonstrated that both receptors were fully functional and could initiate extracellular calcium influx to start PK/PBAN signal transduction. Evaluation of the signaling response of both receptors to PBAN and diapause hormone (DH) revealed a highly sensitive, though differential response. Both receptors responded to PBAN whereas only Spl-PK/PBAN-R exhibited a high response toward DH.

CONCLUSIONS

The structural, electrostatic and cellular functional differences indicate that different PK/PBAN in vivo functions may be mediated by different PK/PBAN receptors and elicited by different peptide(s).

GENERAL SIGNIFICANCE

The results advance our understanding of the mode of action of the PK/PBAN family, and might help in exploring novel high-affinity receptor-specific antagonists that can serve as a basis for the development of new families of insect-control agents.

The Arginine Residue within the C-Terminal Active Core of Bombyx mori Pheromone Biosynthesis-Activating Neuropeptide is Essential for Receptor Binding and Activation

In most lepidopteran insects, the biosynthesis of sex pheromones is regulated by pheromone biosynthesis-activating neuropeptide (PBAN). Bombyx mori PBAN (BomPBAN) consists of 33 amino acid residues and contains a C-terminus FSPRLamide motif as the active core. Among neuropeptides containing the FXPRLamide motif, the arginine (Arg, R) residue at the second position from the C-terminus is highly conserved across several neuropeptides, which can be designated as RXamide peptides. The purpose of this study was to clarify the role of the Arg residue in the BomPBAN active core. We synthesized 10-residue peptides corresponding to the C-terminal part of BomPBAN with a series of replacements at the second position from the C-terminus, termed the C2 position, and measured their efficacy in stimulating Ca(2+) influx in insect cells expressing a fluorescent PBAN receptor chimera (PBANR-EGFP) using the fluorescent Ca(2+) indicator, Fura Red-AM. The PBAN analogs with the C2 position replaced with alanine (Ala, A), aspartic acid (Asp, D), serine (Ser, S), or l-2-aminooctanoic acid (Aoc) decreased PBAN-like activity. R(C2)A (SKTRYFSPALamide) and R(C2)D (SKTRYFSPDLamide) had the lowest activity and could not inhibit the activity of PBAN C10 (SKTRYFSPRLamide). We also prepared Rhodamine Red-labeled peptides of the PBAN analogs and examined their ability to bind PBANR. In contrast to Rhodamine Red-PBAN C10 at 100 nM, none of the synthetic analogs exhibited PBANR binding at the same concentration. Taken together, our results demonstrate that the C2 Arg residue in BomPBAN is essential for PBANR binding and activation.

Neuropeptide signaling in insects

Neuropeptides represent the largest single class of signal compounds and are involved in regulation of development, growth, reproduction, metabolism and behavior of insects. Over the last few years there has been a tremendous increase in our knowledge of neuropeptide signaling due to genome sequencing, peptidomics, gene micro arrays, receptor characterization and targeted gene interference combined with physiological and behavior analysis. In this chapter we review the current knowledge of structure and distribution of insect neuropeptides and their receptors, as well as their diverse functions. We also discuss peptide biosynthesis, processing and expression, as well as classification of insect neuropeptides. Special attention is paid to the role insect neuropeptides play as potential targets for pest management and as a basis for development of insect control agents employing the rational/structural design approaches.

Bioavailability of beta-amino acid and C-terminally derived PK/PBAN analogs

The ability of linear beta-amino acid substituted peptides (PK-betaA-1: Ac-YFT[beta(3)P]RLa; PK-betaA-2: Ac-Y[beta(3)homoF]TPRLa; PK-betaA-3: Ac-Y[beta(3)F]TPRLa; PK-betaA-4: Ac-[beta(3)F]FT[beta(3)P]RLa) and unsubstituted analogs (Ac-YFTPRLa and YFTPRLa) of the pyrokinin(PK)/pheromone biosynthesis-activating neuropeptide (PBAN) family to penetrate the insect cuticle and exert biological activity (i.e., stimulate sex pheromone biosynthesis), was tested by topical application on Heliothis peltigera moths. The present results clearly indicate that small linear synthetic peptides can penetrate the cuticle very efficiently by contact application and activate their target organ. The time responses of the peptides applied in DDW and DMSO were tested and the activities of topically applied and injected peptides were compared. The results clearly indicate that PK-betaA-4 and PK-betaA-3 exhibited high bioavailability (ability to penetrate through the cuticle and exertion of bioactivity) with the latter showing longer persistence in both solvents than any other analog in the study; indicative that incorporation of a beta-amino acid at the Phe(2) position can enhance longevity in topical PK/PBAN analogs. PK-betaA-4 was significantly more active in DMSO than in DDW, and significantly more active than the parent peptide LPK in DMSO. PK-betaA-1 and PK-betaA-2 exhibited negligible activity. Interestingly, Ac-YFTPRLa was highly potent in both solvents; its activity in DDW did not differ from that of PK-betaA-4 and PK-betaA-3, and was higher than that of LPK. Even the unacylated peptide YFTPRLa was active in both solvents, at a similar level to LPK. Topically applied PK-betaA-4 and Ac-YFTPRLa exhibited significantly higher activity than the injected peptides. PK-betaA-3 and YFTPRLa were equally potent in both routes of administration.

PBAN receptor: employment of anti-receptor antibodies for its characterization and for development of a microplate binding assay

This study describes generation of an anti-PBAN receptor (PBAN-R) antiserum and its employment for the characterization of the PK/PBAN-R(s). The antiserum recognized, in a specific and dose-dependent manner, the presence of PBAN-R in pheromone gland membrane preparations of three female moths: Heliothis peltigera, Helicoverpa armigera and Spodoptera littoralis. It also reacted specifically with the S. littoralis larval receptor in vivo, most likely by competing with the ligand on the binding site and consequently inhibiting cuticular melanization. Despite its ability to react with the receptor of H. peltigera in dot blot experiments, the antiserum did not react with the receptor in vivo and failed to inhibit sex pheromone biosynthesis. The antiserum was also used to develop two microplate binding assays. The Ab described in this study is the first raised against an insect neuropeptide (Np) receptor to be used in vivo, and its employment for characterization of the PK/PBAN-R(s) may thus provide important information on the mode of action of this Np family. The present study adds important information on the difference between the receptors in the two moth species, hints at the possible existence of receptor subtypes, and provides a platform for the development of a high-throughput assay (HTA) for screening of PK/PBAN agonists and antagonists.

Bioavailability of insect neuropeptides: the PK/PBAN family as a case study

The ability of unmodified linear peptides to penetrate the insect cuticle and exert bioactivity (e.g., stimulation of sex pheromone biosynthesis) was tested by topical application onto Heliothis peltigera moths of four insect neuropeptides (Nps) of the pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) family: Helicoverpa zea PBAN (Hez-PBAN), Pseudaletia (Mythimna) separata pheromonotropin (PT), Leucophaea maderae PK (LPK) and Locusta migratoria myotropin (Lom-MT-II). The time kinetic of the peptides applied in double distilled water (DDW) or dimethylsulfoxide (DMSO) was tested and the activities of topically applied and injected peptides were compared. The results clearly indicated that all four peptides were highly potent but with differing activities in the two solvents: PBAN was most active in water, and PT in DMSO. The activity of PBAN in DDW lasted up to 8h post-application and its activity in this solvent showed a faster onset and a longer persistence than in DMSO. LPK and MT differed less in their kinetics between the two solvents. Topically applied PBAN at 1 nmol exhibited an equivalent or even significantly higher potency than the injected peptide at several different times post-treatment. Similar results were obtained with topically applied and injected LPK. The present results add important information on the bioavailability of unmodified linear peptides in moths, clearly indicate that linear hydrophilic peptides can penetrate the cuticle by contact application in aqueous solutions and in organic solvents very efficiently, reach their target organ and activate it.

An amphiphilic, PK/PBAN analog is a selective pheromonotropic antagonist that penetrates the cuticle of a heliothine insect

A linear pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) antagonist lead (RYF[dF]PRLa) was structurally modified to impart amphiphilic properties to enhance its ability to transmigrate the hydrophobic cuticle of noctuid moth species and yet retain aqueous solubility in the hemolymph to reach target PK/PBAN receptors within the internal insect environment. The resulting novel PK/PBAN analog, Hex-Suc-A[dF]PRLa (PPK-AA), was synthesized and evaluated as an antagonist in a pheromonotropic assay in Heliothis peltigera against 4 natural PK/PBAN peptide elicitors (PBAN; pheromonotropin, PT; myotropin, MT; leucopyrokinin, LPK) and in a melanotropic assay in Spodoptera littoralis against 3 natural PK/PBAN peptide elicitors (PBAN, PT, LPK). The analog proved to be a potent and efficacious inhibitor of sex pheromone biosynthesis elicited by PBAN (84% at 100 pmol) and PT (54% at 100 pmol), but not by MT and LPK. PPK-AA is a selective pure antagonist (i.e., does not exhibit any agonistic activity) as it failed to inhibit melanization elicited by any of the natural PK/PBAN peptides. The analog was shown to transmigrate isolated cuticle dissected from adult female Heliothis virescens moths to a high extent of 25-30% (130-150 pmol), representing physiologically significant quantities. PPK-AA represents a significant addition to the arsenal of tools available to arthropod endocrinologists studying the endogenous mechanisms of PK/PBAN regulated processes, and a prototype for the development of environmentally friendly pest management agents capable of disrupting the critical process of reproduction.

Inter-phyla studies on neuropeptides: the potential for broad-spectrum anthelmintic and/or endectocide discovery

Flatworm, nematode and arthropod parasites have proven their ability to develop resistance to currently available chemotherapeutics. The heavy reliance on chemotherapy and the ability of target species to develop resistance has prompted the search for novel drug targets. In view of its importance to parasite/pest survival, the neuromusculature of parasitic helminths and pest arthropod species remains an attractive target for the discovery of novel endectocide targets. Exploitation of the neuropeptidergic system in helminths and arthropods has been hampered by a limited understanding of the functional roles of individual peptides and the structure of endogenous targets, such as receptors. Basic research into these systems has the potential to facilitate target characterization and its offshoots (screen development and drug identification). Of particular interest to parasitologists is the fact that selected neuropeptide families are common to metazoan pest species (nematodes, platyhelminths and arthropods) and fulfil specific roles in the modulation of muscle function in each of the three phyla. This article reviews the inter-phyla activity of two peptide families, the FMRFamide-like peptides and allatostatins, on motor function in helminths and arthropods and discusses the potential of neuropeptide signalling as a target system that could uncover novel endectocidal agents.

Inhibition of PK/PBAN-mediated functions in insects: discovery of selective and non-selective inhibitors

The antagonistic properties of a few linear and backbone cyclic (BBC) conformationally constraint peptide libraries and their analogs, were tested for the ability to inhibit pyrokinin/pheromone biosynthesis activating neuropeptide (PK/PBAN) mediated functions: sex pheromone biosynthesis in Heliothis peltigera female moths, cuticular melanization in Spodoptera littoralis larvae, pupariation in the fleshfly Neobellieria bullata and hindgut contraction in Leucophaea maderae, elicited by exogenously injected PBAN, pheromonotropin (PT), leucopyrokinin (LPK), myotropin (MT) or by the endogenous peptides. The data revealed differential inhibitory patterns within the same assay with different elicitors (in both the pheromonotropic and melanotropic assays) and among the different functions and disclosed selective antagonists, hinting at the possibility that the receptors that mediate those functions may differ from one another structurally.

Backbone cyclic pheromone biosynthesis activating neuropeptide (PBAN) antagonists: inhibition of melanization in the moth Spodoptera littoralis (Insecta, Lepidoptera)

Antagonistic and agonistic activities of backbone cyclic (BBC) pheromone biosynthesis activating neuropeptide (PBAN) analogues were evaluated in an attempt to identify potent melanotropic antagonists, to gain an insight into their structure-activity relationship (SAR), and to discover molecules with selective and non-selective melanotropic and pheromonotropic properties. Eight potent melanotropic BBC antagonists and seven agonists were disclosed. SAR studies revealed that the structural requirements of the melanotropic and pheromonotropic agonists and antagonists are different. The cyclic structure of the BBC peptides was unimportant for antagonistic activity, and linearization retained their melanotropic and pheromonotropic antagonistic properties. Comparison of the antagonistic activities of the BBC and precyclic peptides with respect to both functions revealed eight selective antagonists (six that were selective melanotropic antagonists and two selective pheromonotropic antagonists) and four non-selective (melanotropic and pheromonotropic) antagonists. The selective melanotropic antagonists exhibited both, pure or mixed agonistic/antagonistic activities. The selective pheromonotropic compounds were pure antagonists. All non-selective compounds were pure antagonists. Comparison of the agonistic activities of the BBC peptides with respect to both functions revealed six selective melanotropic agonists and one non-selective agonistic compound. All compounds (whether selective or non-selective) exhibited pure agonistic activity. Discovery of the selective compounds hints at the possibility that the receptors that mediate the respective activities may have different properties.

PBAN selective antagonists: inhibition of PBAN induced cuticular melanization and sex pheromone biosynthesis in moths

A D-Phe scan (sequential D-Phe replacement) library of linear peptides, synthesized on the basis of a slightly modified active sequence of PBAN (YFSPRL-amide) was employed to detect potential inhibitors of cuticular melanization in Spodoptera littoralis larvae and to compare their stimulatory and inhibitory melanization activity with their pheromonotropic agonistic and antagonistic activities. A quantitative melanotropic assay was used to monitor the extent of cuticular melanization elicited by Hez-PBAN1-33NH2 in S. littoralis larvae in the presence and absence of the D-Phe peptides. The data revealed the presence of two partial melanotropic antagonists, and disclosed the presence of selective pure melanotropic agonists and pure pheromonotropic antagonists indicating differences in the inhibitory and stimulatory patterns of the library with respect to both activities. The differences between the pheromonotropic and melanotropic inhibitory patterns of the peptides hints at the possibility that sex pheromone biosynthesis in the pheromone gland of Heliothis peltigera females and induction of cuticular melanization in S. littoralis may be mediated by different receptors (that may result either from presence of different receptor sub-types or may reflect species differences in receptor structure and/or properties) despite the fact that they are induced by the same peptide (PBAN1-33NH2).

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

Role of neuropeptides in sex pheromone production in moths

Sex pheromone biosynthesis in many moth species is controlled by a cerebral neuropeptide, termed pheromone biosynthesis activating neuropeptide (PBAN). PBAN is a 33 amino acid C-terminally amidated neuropeptide that is produced by neuroendocrine cells of the subesophageal ganglion (SEG). Studies of the regulation of sex pheromone biosynthesis in moths have revealed that this function can be elicited by additional neuropeptides all of which share the common C-terminal pentapeptide FXPRL-amide (X = S, T, G, V). In the past two decades extensive studies were carried out on the chemical, cellular and molecular aspects of PBAN and the other peptides (termed the pyrokinin (PK)/PBAN family) aiming to understand the mode of their action on sex pheromone biosynthesis. In the present review we focus on a few of these aspects, specifically on the: (i) structure-activity relationship (SAR) of the PK/PBAN family, (ii) characterization of the PK/PBAN receptor and (iii) development of a novel strategy for the generation of PK/PBAN antagonists and their employment in studying the mode of action of the PK/PBAN peptides.

Histochemical localization of the PBAN receptor in the pheromone gland of Heliothis peltigera

The presence of the pyrokinin (PK)/ Pheromone biosynthesis activating neuropeptide (PBAN) receptor in pheromone gland cells of Heliothis peltigera females was demonstrated, and its spatial distribution in the ovipositor was visualized with two photo-affinity biotinilated ligands: BpaPBAN1-33NH(2) and BpaArg(27)-PBAN28-33NH(2). Light microscopy histological studies revealed that the gland is contained within the inter-segmental membrane (ISM) between the 8th and 9th abdominal segments. The gland was found to be composed of a single layer of columnar epithelial cells positioned under the inter-segmental cuticle. Similar epithelial cells were also found in the dorsal and ventral regions of the 9th abdominal segment. All regions containing the glandular cells bound both ligands, indicating presence of the PK/PBAN receptor. The patterns obtained with both ligands were similar, hinting at the possibility that either both ligands bind to the same receptor, or, that if there are two distinct receptors, their spatial distribution throughout the gland is very similar.

In vivo structure-activity studies on the dark-color-inducing neurohormone of locusts

In the 11-residue long dark-color-inducing neurohormone (DCIN = [His7]-corazonin), of locusts, from residue 2 to residue 11, one amino acid at each time was substituted by D-phenylalanine (D-Phe). The dark-color-inducing effect of these peptides was investigated in comparison with unaltered DCIN by a bioassay based on nymphs of a DCIN-deficient albino mutant of the migratory locust, Locusta migratoria. Substitution of any single amino acid by D-Phe always reduced the activity, but did not abolish it completely. Maximum inactivation was obtained after substitution of Gln4, Ser6, or Trp9. The latter two residues are within the partial sequence -Ser-Xxx-Gly-Trp- (Xxx = His in theDCIN) that seems to be important for the dark-color-inducing activity, as found also in another study (Insect Biochem. Mol. Biol.32, 2002, 909). GIn4, however, is outside of this partial sequence.Minimal, although still considerable, inactivation occurred after substitution of Gly8, Phe3, or Asn11, despite the fact that Gly8 is within the -Ser-Xxx-Gly-Trp- partial sequence. In conclusion, no single active core was found, indicating that the whole sequence of the DCIN is necessary to induce maximum darkening effect. No difference was found in the activity of the peptides in which Gly8was substituted by D-Phe or by L-Phe. Therefore the -Ser-Xxx-Gly-Trp- partial sequence does not seem to be stabilized by a type II beta-turn. Nevertheless, existence of another kind of turn that includes this partial sequence is feasible. A single unsuccessful attempt was made to discover an antagonist to the DCIN.

A pheromonotropic peptide of Helicoverpa zea, with melanizing activity, interaction with PBAN, and distribution of immunoreactivity

The sequence of an 18-amino acid residue peptide was deduced from the gene encoding PBAN and other peptides with common C-termini in Helicoverpa zea. The peptide caused melanization in larvae and pheromone production in females of H. zea, and was designated pheromonotropic melanizing peptide (Hez-PMP). The peptide has a 83% sequence homology with a pheromonotropic peptide isolated from Pseudaletia separata. PMP caused melanization and mortality when injected into larvae just before molting. Whereas intense melanization was caused with a dose of 1,000 pmol, peak mortality occurred at 100 pmol, with 50% of larvae dying within 48 h after injection. Pheromonotropic activity of PMP was dose dependent. Co-injection of Hez-PMP and Hez-PBAN into a female resulted in suppression of the pheromonotropic effect of PBAN. Whole-mount immunocytochemical studies revealed PMP-like immunoreactivity in frontal ganglion, subesophageal, thoracic, and abdominal ganglia as well as the esophageal nerve.

In vivo structure-activity studies on the dark-color-inducing neurohormone of locusts

In the 11-residue long dark-color-inducing neurohormone (DCIN = [His7]-corazonin), of locusts, from residue 2 to residue 11, one amino acid at each time was substituted by d-phenylalanine (d-Phe). The dark-color-inducing effect of these peptides was investigated in comparison with unaltered DCIN by a bioassay based on nymphs of a DCIN-deficient albino mutant of the migratory locust, Locusta migratoria. Substitution of any single amino acid by d-Phe always reduced the activity, but did not abolish it completely. Maximum inactivation was obtained after substitution of Gln4, Ser6, or Trp9. The latter two residues are within the partial sequence -Ser-Xxx-Gly-Trp- (Xxx = His in the DCIN) that seems to be important for the dark-color-inducing activity, as found also in another study (Insect Biochem. Mol. Biol. 32, 2002, 909). Gln4, however, is outside of this partial sequence. Minimal, although still considerable, inactivation occurred after substitution of Gly8, Phe3, or Asn11, despite the fact that Gly8 is within the -Ser-Xxx-Gly-Trp- partial sequence. In conclusion, no single active core was found, indicating that the whole sequence of the DCIN is necessary to induce maximum darkening effect. No difference was found in the activity of the peptides in which Gly8 was substituted by d-Phe or by l-Phe. Therefore the -Ser-Xxx-Gly-Trp- partial sequence does not seem to be stabilized by a type II beta-turn. Nevertheless, existence of another kind of turn that includes this partial sequence is feasible. A single unsuccessful attempt was made to discover an antagonist to the DCIN.

Insect neuropeptide antagonists

The development of a new integrated approach to the generation of a novel type of insect neuropeptide (Np) antagonists and putative insect control agents based on backbone cyclic compounds is described. The approach, termed the backbone cyclic neuropeptide-based antagonist (BBC-NBA), was applied to the insect pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN) family as a model, and led to the discovery of a potent linear lead antagonist and several highly potent, metabolically stable BBC antagonists, devoid of agonistic activity, which inhibited PBAN-mediated activities in moths in vivo. This review briefly summarizes our knowledge of insect Nps, describes the PK/PBAN Np family, presents the basic concepts behind the BBC-NBA approach, and introduces the advantages of this method for generation of Np agonists, antagonists and insecticide prototype molecules.

Insect neuropeptide antagonist. Part II. Synthesis and biological activity of backbone cyclic and precyclic PBAN antagonists

A new approach for the design and synthesis of pheromone biosynthesis activating neuropeptide (PBAN) agonists and antagonists using the backbone cyclization and cycloscan concepts is described. Two backbone cyclic (BBC) libraries were synthesized: library I (Ser library) was based on the active C-terminal hexapeptide sequence Tyr-Phe-Ser-Pro-Arg-Leu-NH2 of PBAN1-33NH2; whereas library II (D-Phe library) was based on the sequence of the PBAN lead linear antagonist Arg-Tyr-Phe-d-Phe-Pro-Arg-Leu-NH2. In both libraries the Pro residue was replaced by the BBC building unit Nalpha-(omega-aminoalkyl) Gly having various lengths of alkyl chain. The peptides of the two libraries were tested for agonistic and antagonistic activity. Four precyclic peptides based on two of the BBC antagonists were also synthesized; their activity revealed that a negative charge at the N-terminus of the peptide abolished antagonistic activity. We also describe the use of the reagent SiCl3I for selective deprotection of the Boc group from the building unit prior to on-resin amino-end to backbone-nitrogen (AE-BN) cyclization, during solid-phase synthesis with Fmoc chemistry.

Pyrokinin/PBAN radio-receptor assay: development and application for the characterization of a putative receptor from the pheromone gland of Heliothis peltigera

A radio-receptor assay (RRA) for the insect pyrokinin/PBAN family has been developed. The development involved examination of the ligand (3H-tyrosyl-PBAN28-33NH2)-receptor interaction under various incubation conditions and variations on sex pheromone gland membrane preparation. Application of the RRA for a partial characterization of the putative pyrokinin/PBAN receptor in the pheromone gland of H. peltigera revealed age-dependence of its expression. Pharmacological characterization revealed a high correlation between the binding-affinity to the receptor of various PBAN-derived peptides and their in vivo pheromonotropic bioactivity, and shed light on the interaction of backbone cyclic and linear ([Arg27,D-Phe30]PBAN28-33NH2) PBAN antagonists with the receptor.