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Open AccessEditorial

Insect Receptors: Biochemical, Physiological and Molecular Studies

by Dov Borovsky

Biomolecules 2022, 12(5), 657; https://doi.org/10.3390/biom12050657 - 30 Apr 2022

Viewed by 1473

Abstract

A Biomolecules Special Issue on insect receptors was a great opportunity to invite colleagues from all over the world to contribute original articles and timely reviews on the subject [...] Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

Research

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17 pages, 5465 KiB

Open AccessArticle

The Ribosome Is the Ultimate Receptor for Trypsin Modulating Oostatic Factor (TMOF)

by Dov Borovsky, Pierre Rougé and Robert G. Shatters, Jr.

Biomolecules 2022, 12(4), 577; https://doi.org/10.3390/biom12040577 - 14 Apr 2022

Cited by 4 | Viewed by 2186

Abstract

Aedes aegypti Trypsin Modulating Oostatic Factor (AeaTMOF). a mosquito decapeptide that controls trypsin biosynthesis in female and larval mosquitoes. enters the gut epithelial cells of female mosquitoes using ABC-tmfA receptor/importer. To study the ultimate targeted receptor after AeaTMOF [...] Read more.

Aedes aegypti Trypsin Modulating Oostatic Factor (AeaTMOF). a mosquito decapeptide that controls trypsin biosynthesis in female and larval mosquitoes. enters the gut epithelial cells of female mosquitoes using ABC-tmfA receptor/importer. To study the ultimate targeted receptor after AeaTMOF enters the cell, AeaTMOF was incubated in vitro with either Escherichia coli or Spodoptera frugiperda protein-expressing extracts containing 70S and 80S ribosomes, respectively. The effect of AeaTMOF on luciferase biosynthesis in vitro using 70S ribosomes was compared with that of oncocin112 (1–13), a ribosome-binding antibacterial peptide. The IC₅₀ of 1 μM and 2 μM, respectively, for both peptides was determined. Incubation with a protein-expressing system and S. frugiperda 80S ribosomes determined an IC₅₀ of 1.8 μM for Aedes aegypti larval late trypsin biosynthesis. Incubation of purified E. coli ribosome with increasing concentration of AeaTMOF shows that the binding of AeaTMOF to the bacterial ribosome exhibits a high affinity (K_D = 23 ± 3.4 nM, B_max = 0.553 ± 0.023 pmol/μg ribosome and K_assoc = 4.3 × 10⁷ M⁻¹). Molecular modeling and docking experiments show that AeaTMOF binds bacterial and Drosophila ribosome (50S and 60S, respectively) at the entrance of the ribosome exit tunnel, blocking the tRNA entrance and preventing protein biosynthesis. Recombinant E. coli cells that express only ABC-tmfA importer are inhibited by AeaTMOF but not by oncocin112 (1–13). These results suggest that the ribosome is the ultimate targeted receptor of AeaTMOF. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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10 pages, 652 KiB

Open AccessArticle

Pheromone Receptor Knock-Out Affects Pheromone Detection and Brain Structure in a Moth

by Fotini Koutroumpa, Christelle Monsempès, Sylvia Anton, Marie-Christine François, Nicolas Montagné and Emmanuelle Jacquin-Joly

Biomolecules 2022, 12(3), 341; https://doi.org/10.3390/biom12030341 - 22 Feb 2022

Cited by 7 | Viewed by 2678

Abstract

Sex pheromone receptors are crucial in insects for mate finding and contribute to species premating isolation. Many pheromone receptors have been functionally characterized, especially in moths, but loss of function studies are rare. Notably, the potential role of pheromone receptors in the development [...] Read more.

Sex pheromone receptors are crucial in insects for mate finding and contribute to species premating isolation. Many pheromone receptors have been functionally characterized, especially in moths, but loss of function studies are rare. Notably, the potential role of pheromone receptors in the development of the macroglomeruli in the antennal lobe (the brain structures processing pheromone signals) is not known. Here, we used CRISPR-Cas9 to knock-out the receptor for the major component of the sex pheromone of the noctuid moth Spodoptera littoralis, and investigated the resulting effects on electrophysiological responses of peripheral pheromone-sensitive neurons and on the structure of the macroglomeruli. We show that the inactivation of the receptor specifically affected the responses of the corresponding antennal neurons did not impact the number of macroglomeruli in the antennal lobe but reduced the size of the macroglomerulus processing input from neurons tuned to the main pheromone component. We suggest that this mutant neuroanatomical phenotype results from a lack of neuronal activity due to the absence of the pheromone receptor and potentially reduced neural connectivity between peripheral and antennal lobe neurons. This is the first evidence of the role of a moth pheromone receptor in macroglomerulus development and extends our knowledge of the different functions odorant receptors can have in insect neurodevelopment. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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21 pages, 44025 KiB

Open AccessEditor’s ChoiceArticle

A Comparative Evaluation of the Structural and Dynamic Properties of Insect Odorant Binding Proteins

by George Tzotzos

Biomolecules 2022, 12(2), 282; https://doi.org/10.3390/biom12020282 - 9 Feb 2022

Cited by 2 | Viewed by 2441

Abstract

Insects devote a major part of their metabolic resources to the production of odorant binding proteins (OBPs). Although initially, these proteins were implicated in the solubilisation, binding and transport of semiochemicals to olfactory receptors, it is now recognised that they may play diverse, [...] Read more.

Insects devote a major part of their metabolic resources to the production of odorant binding proteins (OBPs). Although initially, these proteins were implicated in the solubilisation, binding and transport of semiochemicals to olfactory receptors, it is now recognised that they may play diverse, as yet uncharacterised, roles in insect physiology. The structures of these OBPs, the majority of which are known as “classical” OBPs, have shed some light on their potential functional roles. However, the dynamic properties of these proteins have received little attention despite their functional importance. Structural dynamics are encoded in the native protein fold and enable the adaptation of proteins to substrate binding. This paper provides a comparative review of the structural and dynamic properties of OBPs, making use of sequence/structure analysis, statistical and theoretical physics-based methods. It provides a new layer of information and additional methodological tools useful in unravelling the relationship between structure, dynamics and function of insect OBPs. The dynamic properties of OBPs, studied by means of elastic network models, reflect the similarities/dissimilarities observed in their respective structures and provides insights regarding protein motions that may have important implications for ligand recognition and binding. Furthermore, it was shown that the OBPs studied in this paper share conserved structural ‘core’ that may be of evolutionary and functional importance. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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14 pages, 5715 KiB

Open AccessArticle

Mutually Exclusive Expression of Closely Related Odorant-Binding Proteins 9A and 9B in the Antenna of the Red Flour Beetle Tribolium castaneum

by Alice Montino, Karthi Balakrishnan, Stefan Dippel, Björn Trebels, Piotr Neumann and Ernst A. Wimmer

Biomolecules 2021, 11(10), 1502; https://doi.org/10.3390/biom11101502 - 12 Oct 2021

Cited by 5 | Viewed by 2837

Abstract

Olfaction is crucial for insects to find food sources, mates, and oviposition sites. One of the initial steps in olfaction is facilitated by odorant-binding proteins (OBPs) that translocate hydrophobic odorants through the aqueous olfactory sensilla lymph to the odorant receptor complexes embedded in [...] Read more.

Olfaction is crucial for insects to find food sources, mates, and oviposition sites. One of the initial steps in olfaction is facilitated by odorant-binding proteins (OBPs) that translocate hydrophobic odorants through the aqueous olfactory sensilla lymph to the odorant receptor complexes embedded in the dendritic membrane of olfactory sensory neurons. The Tribolium castaneum (Coleoptera, Tenebrionidae) OBPs encoded by the gene pair TcasOBP9A and TcasOBP9B represent the closest homologs to the well-studied Drosophila melanogaster OBP Lush (DmelOBP76a), which mediates pheromone reception. By an electroantennographic analysis, we can show that these two OBPs are not pheromone-specific but rather enhance the detection of a broad spectrum of organic volatiles. Both OBPs are expressed in the antenna but in a mutually exclusive pattern, despite their homology and gene pair character by chromosomal location. A phylogenetic analysis indicates that this gene pair arose at the base of the Cucujiformia, which dates the gene duplication event to about 200 Mio years ago. Therefore, this gene pair is not the result of a recent gene duplication event and the high sequence conservation in spite of their expression in different sensilla is potentially the result of a common function as co-OBPs. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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13 pages, 1580 KiB

Open AccessArticle

Opposing Actions of Octopamine and Tyramine on Honeybee Vision

by Felix Schilcher, Markus Thamm, Martin Strube-Bloss and Ricarda Scheiner

Biomolecules 2021, 11(9), 1374; https://doi.org/10.3390/biom11091374 - 17 Sep 2021

Cited by 7 | Viewed by 3661

Abstract

The biogenic amines octopamine and tyramine are important neurotransmitters in insects and other protostomes. They play a pivotal role in the sensory responses, learning and memory and social organisation of honeybees. Generally, octopamine and tyramine are believed to fulfil similar roles as their [...] Read more.

The biogenic amines octopamine and tyramine are important neurotransmitters in insects and other protostomes. They play a pivotal role in the sensory responses, learning and memory and social organisation of honeybees. Generally, octopamine and tyramine are believed to fulfil similar roles as their deuterostome counterparts epinephrine and norepinephrine. In some cases opposing functions of both amines have been observed. In this study, we examined the functions of tyramine and octopamine in honeybee responses to light. As a first step, electroretinography was used to analyse the effect of both amines on sensory sensitivity at the photoreceptor level. Here, the maximum receptor response was increased by octopamine and decreased by tyramine. As a second step, phototaxis experiments were performed to quantify the behavioural responses to light following treatment with either amine. Octopamine increased the walking speed towards different light sources while tyramine decreased it. This was independent of locomotor activity. Our results indicate that tyramine and octopamine act as functional opposites in processing responses to light. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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21 pages, 7495 KiB

Open AccessArticle

Cloning and Characterization of Aedes aegypti Trypsin Modulating Oostatic Factor (TMOF) Gut Receptor

by Dov Borovsky, Kato Deckers, Anne Catherine Vanhove, Maud Verstraete, Pierre Rougé, Robert G. Shatters, Jr. and Charles A. Powell

Biomolecules 2021, 11(7), 934; https://doi.org/10.3390/biom11070934 - 23 Jun 2021

Cited by 8 | Viewed by 2593

Abstract

Trypsin Modulating Oostatic Factor (TMOF) receptor was solubilized from the guts of female Ae. Aegypti and cross linked to His₆-TMOF and purified by Ni affinity chromatography. SDS PAGE identified two protein bands (45 and 61 kDa). The bands were cut digested [...] Read more.

Trypsin Modulating Oostatic Factor (TMOF) receptor was solubilized from the guts of female Ae. Aegypti and cross linked to His₆-TMOF and purified by Ni affinity chromatography. SDS PAGE identified two protein bands (45 and 61 kDa). The bands were cut digested and analyzed using MS/MS identifying a protein sequence (1306 amino acids) in the genome of Ae. aegypti. The mRNA of the receptor was extracted, the cDNA sequenced and cloned into pTAC-MAT-2. E. coli SbmA⁻ was transformed with the recombinant plasmid and the receptor was expressed in the inner membrane of the bacterial cell. The binding kinetics of TMOF-FITC was then followed showing that the cloned receptor exhibits high affinity to TMOF (K_D = 113.7 ± 18 nM ± SEM and B_max = 28.7 ± 1.8 pmol ± SEM). Incubation of TMOF-FITC with E. coli cells that express the receptor show that the receptor binds TMOF and imports it into the bacterial cells, indicating that in mosquitoes the receptor imports TMOF into the gut epithelial cells. A 3D modeling of the receptor indicates that the receptor has ATP binding sites and TMOF transport into recombinant E. coli cells is inhibited with ATPase inhibitors Na Arsenate and Na Azide. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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16 pages, 6857 KiB

Open AccessArticle

Insights into the Activation of a Crustacean G Protein-Coupled Receptor: Evaluation of the Red Pigment-Concentrating Hormone Receptor of the Water Flea Daphnia pulex (Dappu-RPCH R)

by Graham E. Jackson and Gerd Gäde

Biomolecules 2021, 11(5), 710; https://doi.org/10.3390/biom11050710 - 10 May 2021

Cited by 3 | Viewed by 2164

Abstract

The validation of a previously developed model of the interaction between the red pigment-concentrating hormone of Daphnia pulex and its cognate receptor (Jackson et al., IJBM 106, 969–978, 2018) was undertaken. Single amino acid replacements, noticeably an Ala scan, of the ligand, Dappu-RPCH, [...] Read more.

The validation of a previously developed model of the interaction between the red pigment-concentrating hormone of Daphnia pulex and its cognate receptor (Jackson et al., IJBM 106, 969–978, 2018) was undertaken. Single amino acid replacements, noticeably an Ala scan, of the ligand, Dappu-RPCH, were docked to the receptor, and the binding energies calculated and compared to the one with Dappu-RPCH. As a second step, the same molecules were docked using molecular dynamics (MD) in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane. Changes in binding energy were compared to previous results on in vitro receptor activation (Marco et al., Sci. Rep. 7, 6851, 2017). Residue scanning and MD simulations both gave comparable results for binding energy. For most mutants, there was a good inverse correlation between in vitro activity and binding. There were, however, exceptions; for example: [Ala4]Dappu-RPCH bound as tightly as the cognate ligand but had little activity. This seeming discrepancy was explained when the MD data were analyzed in detail, showing that, although [Ala4]Dappu-RPCH had multiple interactions with the receptor accounting for the high binding energy, the interacting residues of the receptor were quite different to those of Dappu-RPCH. The MD calculations show clearly that the strong binding affinity of the ligand to the receptor is not sufficient for activation. Interaction of the binding of the ligand to two residues of the receptor, Ser 155 and Gln 237, is also essential. A comparison of our computational results with the experimental results of Marco et al. and comparison with the extensive data on GnRH supports the validity of our Dappu-RPCH R model. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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12 pages, 997 KiB

Open AccessArticle

GPCR-Based Bioactive Peptide Screening Using Phage-Displayed Peptides and an Insect Cell System for Insecticide Discovery

by Man-Yeon Choi and Robert K. Vander Meer

Biomolecules 2021, 11(4), 583; https://doi.org/10.3390/biom11040583 - 16 Apr 2021

Cited by 10 | Viewed by 6900

Abstract

The discovery of new insecticides improves integrated pest management (IPM), but is usually a long high-risk process with a low probability of success. For over two decades, insect neuropeptides (NPs) and their G-protein coupled receptors (GPCRs) have been considered as biological targets for [...] Read more.

The discovery of new insecticides improves integrated pest management (IPM), but is usually a long high-risk process with a low probability of success. For over two decades, insect neuropeptides (NPs) and their G-protein coupled receptors (GPCRs) have been considered as biological targets for insect pest control, because they are involved in almost all physiological processes associated with insect life stages. A key roadblock to success has been the question of how large volume chemical libraries can be efficiently screened for active compounds. New genomic and proteomic tools have advanced and facilitated the development of new approaches to insecticide discovery. In this study, we report a novel GPCR-based screening technology that uses millions of short peptides randomly generated by bacteriophages, and a method using an insect Sf9 cell expression system. The fire ant is a good model system, since bioactive peptides have been identified for a specific GPCR. The novel small peptides could interfere with the target GPCR-ligand functions. Therefore, we refer to this new mechanism as “receptor interference” (RECEPTORi). The GPCR-based bioactive peptide screening method offers multiple advantages. Libraries of phage-displayed peptides (~10⁹ peptides) are inexpensive. An insect cell-based screening system rapidly leads to target specific GPCR agonists or antagonists in weeks. Delivery of bioactive peptides to target pests can be flexible, such as topical, ingestion, and plant-incorporated protectants. A variety of GPCR targets are available, thus minimizing the development of potential insecticide resistance. This report provides the first proof-of-concept for the development of novel arthropod pest management strategies using neuropeptides, and GPCRs. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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21 pages, 1762 KiB

Open AccessArticle

Crucial Role of Juvenile Hormone Receptor Components Methoprene-Tolerant and Taiman in Sexual Maturation of Adult Male Desert Locusts

by Michiel Holtof, Joachim Van Lommel, Marijke Gijbels, Elfie Dekempeneer, Bart Nicolai, Jozef Vanden Broeck and Elisabeth Marchal

Biomolecules 2021, 11(2), 244; https://doi.org/10.3390/biom11020244 - 9 Feb 2021

Cited by 12 | Viewed by 3010

Abstract

Currently (2020), Africa and Asia are experiencing the worst desert locust (Schistocerca gregaria) plague in decades. Exceptionally high rainfall in different regions caused favorable environmental conditions for very successful reproduction and population growth. To better understand the molecular mechanisms responsible for [...] Read more.

Currently (2020), Africa and Asia are experiencing the worst desert locust (Schistocerca gregaria) plague in decades. Exceptionally high rainfall in different regions caused favorable environmental conditions for very successful reproduction and population growth. To better understand the molecular mechanisms responsible for this remarkable reproductive capacity, as well as to fill existing knowledge gaps regarding the regulation of male reproductive physiology, we investigated the role of methoprene-tolerant (Scg-Met) and Taiman (Scg-Tai), responsible for transducing the juvenile hormone (JH) signal, in adult male locusts. We demonstrated that knockdown of these components by RNA interference strongly inhibits male sexual maturation, severely disrupting reproduction. This was evidenced by the inability to show mating behavior, the absence of a yellow-colored cuticle, the reduction of relative testes weight, and the drastically reduced phenylacetonitrile (PAN) pheromone levels of the treated males. We also observed a reduced relative weight, as well as relative protein content, of the male accessory glands in Scg-Met knockdown locusts. Interestingly, in these animals the size of the corpora allata (CA), the endocrine glands where JH is synthesized, was significantly increased, as well as the transcript level of JH acid methyltransferase (JHAMT), a rate-limiting enzyme in the JH biosynthesis pathway. Moreover, other endocrine pathways appeared to be affected by the knockdown, as evidenced by changes in the expression levels of the insulin-related peptide and two neuroparsins in the fat body. Our results demonstrate that JH signaling pathway components play a crucial role in male reproductive physiology, illustrating their potential as molecular targets for pest control. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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Review

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47 pages, 2730 KiB

Open AccessReview

A Comparative Perspective on Functionally-Related, Intracellular Calcium Channels: The Insect Ryanodine and Inositol 1,4,5-Trisphosphate Receptors

by Umut Toprak, Cansu Doğan and Dwayne Hegedus

Biomolecules 2021, 11(7), 1031; https://doi.org/10.3390/biom11071031 - 15 Jul 2021

Cited by 15 | Viewed by 5101

Abstract

Calcium (Ca²⁺) homeostasis is vital for insect development and metabolism, and the endoplasmic reticulum (ER) is a major intracellular reservoir for Ca²⁺. The inositol 1,4,5- triphosphate receptor (IP₃R) and ryanodine receptor (RyR) are large homotetrameric channels associated [...] Read more.

Calcium (Ca²⁺) homeostasis is vital for insect development and metabolism, and the endoplasmic reticulum (ER) is a major intracellular reservoir for Ca²⁺. The inositol 1,4,5- triphosphate receptor (IP₃R) and ryanodine receptor (RyR) are large homotetrameric channels associated with the ER and serve as two major actors in ER-derived Ca²⁺ supply. Most of the knowledge on these receptors derives from mammalian systems that possess three genes for each receptor. These studies have inspired work on synonymous receptors in insects, which encode a single IP₃R and RyR. In the current review, we focus on a fundamental, common question: “why do insect cells possess two Ca²⁺ channel receptors in the ER?”. Through a comparative approach, this review covers the discovery of RyRs and IP₃Rs, examines their structures/functions, the pathways that they interact with, and their potential as target sites in pest control. Although insects RyRs and IP₃Rs share structural similarities, they are phylogenetically distinct, have their own structural organization, regulatory mechanisms, and expression patterns, which explains their functional distinction. Nevertheless, both have great potential as target sites in pest control, with RyRs currently being targeted by commercial insecticide, the diamides. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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27 pages, 12234 KiB

Open AccessEditor’s ChoiceReview

The 40-Year Mystery of Insect Odorant-Binding Proteins

by Karen Rihani, Jean-François Ferveur and Loïc Briand

Biomolecules 2021, 11(4), 509; https://doi.org/10.3390/biom11040509 - 30 Mar 2021

Cited by 110 | Viewed by 8962

Abstract

The survival of insects depends on their ability to detect molecules present in their environment. Odorant-binding proteins (OBPs) form a family of proteins involved in chemoreception. While OBPs were initially found in olfactory appendages, recently these proteins were discovered in other chemosensory and [...] Read more.

The survival of insects depends on their ability to detect molecules present in their environment. Odorant-binding proteins (OBPs) form a family of proteins involved in chemoreception. While OBPs were initially found in olfactory appendages, recently these proteins were discovered in other chemosensory and non-chemosensory organs. OBPs can bind, solubilize and transport hydrophobic stimuli to chemoreceptors across the aqueous sensilla lymph. In addition to this broadly accepted “transporter role”, OBPs can also buffer sudden changes in odorant levels and are involved in hygro-reception. The physiological roles of OBPs expressed in other body tissues, such as mouthparts, pheromone glands, reproductive organs, digestive tract and venom glands, remain to be investigated. This review provides an updated panorama on the varied structural aspects, binding properties, tissue expression and functional roles of insect OBPs. Full article

(This article belongs to the Special Issue Insect Receptors: Biochemical, Physiological and Molecular Studies)

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