Hormone-like peptides in the venoms of marine cone snails

Main methods and tools for peptide development based on protein-protein interactions (PPIs)

Protein-protein interactions (PPIs) regulate essential physiological and pathological processes. Due to their large and shallow binding surfaces, PPIs are often considered challenging drug targets for small molecules. Peptides offer a viable alternative, as they can bind these targets, acting as regulators or mimicking interaction partners. This review focuses on competitive peptides, a class of orthosteric modulators that disrupt PPI formation. We provide a concise yet comprehensive overview of recent advancements in in-silico peptide design, highlighting computational strategies that have improved the efficiency and accuracy of PPI-targeting peptides. Additionally, we examine cutting-edge experimental methods for evaluating PPI-based peptides. By exploring the interplay between computational design and experimental validation, this review presents a structured framework for developing effective peptide therapeutics targeting PPIs in various diseases.

In silico identification of neuropeptide genes encoded by the genome of Crassostrea virginica with a special emphasis on feeding-related genes

Suspension-feeding bivalves, including the oyster Crassostrea virginica, use mucosal lectins to capture food particles. For instance, oysters can increase the transcription of these molecules to enhance food uptake. However, the regulatory processes influencing food uptake remain unclear although likely involve neuropeptides. Information on the neuropeptidome of C. virginica is limited, hindering the comprehension of its physiology, including energy homeostasis. This study explored the genome of C. virginica to identify neuropeptide precursors in silico and compared these with orthologs from other mollusks. A special focus was given to genes with potential implication in feeding processes. qPCR was used to determine the main organs of transcription of feeding-related genes. To further probe the function of target neuropeptides, visceral ganglia extracts and synthetic NPF were injected into oysters to evaluate their impact on genes associated with feeding and energy homeostasis. A total of eighty-five neuropeptides genes were identified in C. virginica genome. About 50 % of these are suggested to play a role in feeding processes. qPCR analyses showed that visceral ganglia and digestive system are the main organs for the synthesis of feeding-related neuropeptides. Further, results showed that the transcription of several neuropeptide genes in the visceral ganglia, including NPF and insulin-like peptide, increased after starvation. Finally, the injection of visceral ganglia extracts and synthetic NPF increased the transcription of a mucosal lectin and a glycogen synthase, known to be involved in food capture and glucose storage. Overall, this study identifies key genes regulating oyster physiology, enhancing the understanding of the control of basic physiological mechanisms in C. virginica.

Venoms of Lepidoptera: Evolution, Composition, and Molecular Modes of Action

Animal venoms are a focus of research due to the hazards they represent and to their relationship to evolution and ecology, pharmacology, biodiscovery, and biotechnology. Venoms have evolved multiple times in Lepidoptera, mostly as defensive adaptations that protect the larval life stages. While venoms are always produced in structures derived from cuticle and setae, they are diverse in their composition and bioactivity, reflecting their multiple evolutionary origins. The most common result of envenomation by lepidopterans is pain and inflammation, but envenomation by some species causes fatal hemorrhagic syndromes or chronic inflammatory conditions in humans or veterinary pathologies such as equine amnionitis and fetal loss. The handful of lepidopteran venom toxins that have been characterized includes coagulotoxins from Lonomia obliqua (Saturniidae) and pain-causing cecropin-like peptides from Doratifera vulnerans (Limacodidae). However, our knowledge of lepidopteran venoms remains comparatively poor, with further studies required to yield a clear picture of the evolution, composition, and function of venoms produced by Lepidoptera.

Allatotropin (AT) related peptides L-ATRP and D2-ATRP diastereomers activate an endogenous receptor and suppress heart rate in the Pacific abalone Haliotis discus hannai

Allatotropin (AT) has been identified in many insects and plays important roles in the regulation of their intestinal contraction, heart rate, ion transport, and digestive enzyme secretion. However, information on AT-related bioinformatics in other animal phyla is scarce. In this study, we cloned a full-length cDNA encoding the AT-related peptide receptor (ATRPR) of the abalone Haliotis discus hannai (Hdh) and further characterized Hdh-ATRPR with its potential ligands, Hdh-ATRPs. In luciferase reporter and Ca2+ mobilization assays, Hdh-ATRPs, including a D-type Phe at the second amino acid position, Hdh-D2-ATRP, activated Hdh-ATRPR in a dose-dependent manner, whereas all-L-type Hdh-ATRP was a more potent ligand than Hdh-D2-ATRP. Furthermore, Hdh-ATRPs induced ERK1/2 phosphorylation in Hdh-ATRPR-expressing HEK293 cells, which was dose-dependently abolished by the PKC inhibitor Gö6983. The heart rate decreased significantly within 10 min when Hdh-D2-ATRP was injected into the adduct muscle sinus of abalone (0.2 or 1.0 µg/g body weight), while the abalone injected with a high concentration of Hdh-D2-ATRP (1.5 μg/g body weight) were sublethal within 5 h. Thus, Hdh-ATRP signaling is primarily linked to the Gαq/PKC and is possibly associated with heart rate regulation in abalone.

Fish-hunting cone snail disrupts prey's glucose homeostasis with weaponized mimetics of somatostatin and insulin

Venomous animals have evolved diverse molecular mechanisms to incapacitate prey and defend against predators. Most venom components disrupt nervous, locomotor, and cardiovascular systems or cause tissue damage. The discovery that certain fish-hunting cone snails use weaponized insulins to induce hypoglycemic shock in prey highlights a unique example of toxins targeting glucose homeostasis. Here, we show that, in addition to insulins, the deadly fish hunter, Conus geographus, uses a selective somatostatin receptor 2 (SSTR2) agonist that blocks the release of the insulin-counteracting hormone glucagon, thereby exacerbating insulin-induced hypoglycemia in prey. The native toxin, Consomatin nG1, exists in several proteoforms with a minimized vertebrate somatostatin-like core motif connected to a heavily glycosylated N-terminal region. We demonstrate that the toxin's N-terminal tail closely mimics a glycosylated somatostatin from fish pancreas and is crucial for activating the fish SSTR2. Collectively, these findings provide a stunning example of chemical mimicry, highlight the combinatorial nature of venom components, and establish glucose homeostasis as an effective target for prey capture.

Prey Shifts Drive Venom Evolution in Cone Snails

Venom systems are complex traits that have independently emerged multiple times in diverse plant and animal phyla. Within each venomous lineage there typically exists interspecific variation in venom composition where several factors have been proposed as drivers of variation, including phylogeny and diet. Understanding these factors is of broad biological interest and has implications for the development of antivenom therapies and venom-based drug discovery. Because of their high species richness and the presence of several major evolutionary prey shifts, venomous marine cone snails (genus Conus) provide an ideal system to investigate drivers of interspecific venom variation. Here, by analyzing the venom gland expression profiles of ∼3,000 toxin genes from 42 species of cone snail, we elucidate the role of prey-specific selection pressures in shaping venom variation. By analyzing overall venom composition and individual toxin structures, we demonstrate that the shifts from vermivory to piscivory in Conus are complemented by distinct changes in venom composition independent of phylogeny. In vivo injections of venom from piscivorous cone snails in fish further showed a higher potency compared with venom of nonpiscivores demonstrating a selective advantage. Together, our findings provide compelling evidence for the role of prey shifts in directing the venom composition of cone snails and expand our understanding of the mechanisms of venom variation and diversification.

Cysteine-free cone snail venom peptides: Classification of precursor proteins and identification of mature peptides

The cysteine-free acyclic peptides present in marine cone snail venom have been much less investigated than their disulfide bonded counterparts. Precursor protein sequences derived from transcriptomic data, together with mass spectrometric fragmentation patterns for peptides present in venom duct tissue extracts, permit the identification of mature peptides. Twelve distinct gene superfamiles have been identified with precursor lengths between 64 and 158 residues. In the case of Conus monile, three distinct mature peptides have been identified, arising from two distinct protein precursors. Mature acyclic peptides are often post-translationally modified, with C-terminus amidation, a feature characteristic of neuropeptides. In the present study, 20 acyclic peptides from Conus monile and Conus betulinus were identified. The common modifications of C-terminus amidation, gamma carboxylation of glutamic acid (E to ϒ), N-terminus conversion of Gln (Q) to a pyroglutamyl residue (Z), and hydroxylation of Pro (P) to Hyp (O) are observed in one or more peptides identified in this study. Proteolytic trimming of sequences by cleavage at the C-terminus of Asn (N) residues is established. The presence of an asparagine endopeptidase is strengthened by the identification of legumain-like sequences in the transcriptome assemblies from diverse Conus species. Such sequences may be expected to have a cleavage specificity at Asn-Xxx peptide bonds.

Predatory and Defensive Strategies in Cone Snails

Cone snails are carnivorous marine animals that prey on fish (piscivorous), worms (vermivorous), or other mollusks (molluscivorous). They produce a complex venom mostly made of disulfide-rich conotoxins and conopeptides in a compartmentalized venom gland. The pharmacology of cone snail venom has been increasingly investigated over more than half a century. The rising interest in cone snails was initiated by the surprising high human lethality rate caused by the defensive stings of some species. Although a vast amount of information has been uncovered on their venom composition, pharmacological targets, and mode of action of conotoxins, the venom-ecology relationships are still poorly understood for many lineages. This is especially important given the relatively recent discovery that some species can use different venoms to achieve rapid prey capture and efficient deterrence of aggressors. Indeed, via an unknown mechanism, only a selected subset of conotoxins is injected depending on the intended purpose. Some of these remarkable venom variations have been characterized, often using a combination of mass spectrometry and transcriptomic methods. In this review, we present the current knowledge on such specific predatory and defensive venoms gathered from sixteen different cone snail species that belong to eight subgenera: Pionoconus, Chelyconus, Gastridium, Cylinder, Conus, Stephanoconus, Rhizoconus, and Vituliconus. Further studies are needed to help close the gap in our understanding of the evolved ecological roles of many cone snail venom peptides.

Diversity and Evolutionary Analysis of Venom Insulin Derived from Cone Snails

Cone snails possess a diverse array of novel peptide toxins, which selectively target ion channels and receptors in the nervous and cardiovascular systems. These numerous novel peptide toxins are a valuable resource for future marine drug development. In this review, we compared and analyzed the sequence diversity, three-dimensional structural variations, and evolutionary aspects of venom insulin derived from different cone snail species. The comparative analysis reveals that there are significant variations in the sequences and three-dimensional structures of venom insulins from cone snails with different feeding habits. Notably, the venom insulin of some piscivorous cone snails exhibits a greater similarity to humans and zebrafish insulins. It is important to emphasize that these venom insulins play a crucial role in the predatory strategies of these cone snails. Furthermore, a phylogenetic tree was constructed to trace the lineage of venom insulin sequences, shedding light on the evolutionary interconnections among cone snails with diverse diets.

Proteomic characterization and biological activities of the mucus produced by the zoanthid Palythoa caribaeorum (Duchassaing & Michelotti, 1860)

Mucus, produced by Palythoa caribaeorum has been popularly reported due to healing, anti-inflammatory, and analgesic effects. However, biochemical and pharmacological properties of this mucus remains unexplored. Therefore, the present study aimed to study its proteome profile by 2DE electrophoresis and MALDI-TOF. Furthermore, it was evaluated the cytotoxic, antibacterial, and antioxidant activities of the mucus and from its protein extract (PE). Proteomics study identified14 proteins including proteins involved in the process of tissue regeneration and death of tumor cells. The PE exhibited cell viability below 50% in the MCF-7 and S-180 strains. It showed IC50 of 6.9 μg/mL for the J774 lineage, and also, favored the cellular growth of fibroblasts. Furthermore, PE revealed activity against Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, and Staphylococcus epidermidis (MIC of 250 μg/mL). These findings revealed the mucus produced by Palythoa caribaeorum with biological activities, offering alternative therapies for the treatment of cancer and as a potential antibacterial agent.

Collaborative Expression: Transcriptomics of Conus virgo Suggests Contribution of Multiple Secretory Glands to Venom Production

Venomous marine gastropods of the family Conidae are among the most diversified predators in marine realm-in large due to their complex venoms. Besides being a valuable source of bioactive neuropeptides conotoxins, cone-snails venoms are an excellent model for molecular evolution studies, addressing origin of key innovations. However, these studies are handicapped by scarce current knowledge on the tissues involved in venom production, as it is generally assumed the sole prerogative of the venom gland (VG). The role of other secretory glands that are present in all Conus species (salivary gland, SG) or only in some species (accessory salivary gland, ASG) remains poorly understood. Here, for the first time, we carry out a detailed analysis of the VG, SG, and ASG transcriptomes in the vermivorous Conus virgo. We detect multiple transcripts clusters in both the SG and ASG, whose annotations imply venom-related functions. Despite the subsets of transcripts highly-expressed in the VG, SG, and ASG being very distinct, SG expresses an L-, and ASG-Cerm08-, and MEFRR- superfamily conotoxins, all previously considered specific for VG. We corroborate our results with the analysis of published SG and VG transcriptomes from unrelated fish-hunting C. geographus, and C. striatus, possibly fish-hunting C. rolani, and worm-hunting Conus quercinus. In spite of low expression levels of conotoxins, some other specific clusters of putative venom-related peptides are present and may be highly expressed in the SG of these species. Further functional studies are necessary to determine the role that these peptides play in envenomation. In the meantime, our results show importance of routine multi-tissue sampling both for accurate interpretation of tissue-specific venom composition in cone-snails, and for better understanding origin and evolution of venom peptides genes.

Control of postprandial hyperglycemia by oral administration of the sea anemone mucus-derived α-amylase inhibitor (magnificamide)

Diabetes mellitus is a serious threat to human health in both developed and developing countries. Optimal disease control requires the use of a diet and a combination of several medications, including oral hypoglycemic agents such as α-glucosidase inhibitors. Currently, the arsenal of available drugs is insufficient, which determines the relevance of studying new potent α-amylase inhibitors. We implemented the recombinant production of sea anemone derived α-amylase inhibitor magnificamide in Escherichia coli. Peptide was isolated by a combination of liquid chromatography techniques. Its folding and molecular weight was proved by 1H NMR and mass spectrometry. The Ki value of magnificamide against human pancreatic α-amylase is 3.1 nM according to Morrison equation for tight binding inhibitors. Our study of the thermodynamic characteristics of binding of magnificamide to human salivary and pancreatic α-amylases by isothermal titration calorimetry showed the presence of different binding mechanisms with Kd equal to 0.11 µM and 0.1 nM, respectively. Experiments in mice with streptozotocin-induced diabetes mimicking diabetes mellitus type 1 were used to study the efficiency of magnificamide against postprandial hyperglycemia. It was found that at a dose of 0.005 mg kg-1, magnificamide effectively blocks starch breakdown and prevents the development of postprandial hyperglycemia in T1D mice. Our results demonstrated the therapeutic potential of magnificamide for the control of postprandial hyperglycemia.

Venom composition and bioactive RF-amide peptide toxins of the saddleback caterpillar, Acharia stimulea (Lepidoptera: Limacodidae)

Limacodidae is a family of lepidopteran insects comprising >1500 species. More than half of these species produce pain-inducing defensive venoms in the larval stage, but little is known about their venom toxins. Recently, we characterised proteinaceous toxins from the Australian limacodid caterpillar Doratifera vulnerans, but it is unknown if the venom of this species is typical of other Limacodidae. Here, we use single animal transcriptomics and venom proteomics to investigate the venom of an iconic limacodid, the North American saddleback caterpillar Acharia stimulea. We identified 65 venom polypeptides, grouped into 31 different families. Neurohormones, knottins, and homologues of the immune signaller Diedel make up the majority of A.stimulea venom, indicating strong similarities to D. vulnerans venom, despite the large geographic separation of these caterpillars. One notable difference is the presence of RF-amide peptide toxins in A. stimulea venom. Synthetic versions of one of these RF-amide toxins potently activated the human neuropeptide FF1 receptor, displayed insecticidal activity when injected into Drosophila melanogaster, and moderately inhibited larval development of the parasitic nematode Haemonchus contortus. This study provides insights into the evolution and activity of venom toxins in Limacodidae, and provides a platform for future structure-function characterisation of A.stimulea peptide toxins.

Ancestral glycoprotein hormone-receptor pathway controls growth in C. elegans

In vertebrates, thyrostimulin is a highly conserved glycoprotein hormone that, besides thyroid stimulating hormone (TSH), is a potent ligand of the TSH receptor. Thyrostimulin is considered the most ancestral glycoprotein hormone and orthologs of its subunits, GPA2 and GPB5, are widely conserved across vertebrate and invertebrate animals. Unlike TSH, however, the functions of the thyrostimulin neuroendocrine system remain largely unexplored. Here, we identify a functional thyrostimulin-like signaling system in Caenorhabditis elegans. We show that orthologs of GPA2 and GPB5, together with thyrotropin-releasing hormone (TRH) related neuropeptides, constitute a neuroendocrine pathway that promotes growth in C. elegans. GPA2/GPB5 signaling is required for normal body size and acts through activation of the glycoprotein hormone receptor ortholog FSHR-1. C. elegans GPA2 and GPB5 increase cAMP signaling by FSHR-1 in vitro. Both subunits are expressed in enteric neurons and promote growth by signaling to their receptor in glial cells and the intestine. Impaired GPA2/GPB5 signaling causes bloating of the intestinal lumen. In addition, mutants lacking thyrostimulin-like signaling show an increased defecation cycle period. Our study suggests that the thyrostimulin GPA2/GPB5 pathway is an ancient enteric neuroendocrine system that regulates intestinal function in ecdysozoans, and may ancestrally have been involved in the control of organismal growth.

Identification of three elevenin receptors and roles of elevenin disulfide bond and residues in receptor activation in Aplysia californica

Neuropeptides are ubiquitous intercellular signaling molecules in the CNS and play diverse roles in modulating physiological functions by acting on specific G-protein coupled receptors (GPCRs). Among them, the elevenin signaling system is now believed to be present primarily in protostomes. Although elevenin was first identified from the L11 neuron of the abdominal ganglion in mollusc Aplysia californica, no receptors have been described in Aplysia, nor in any other molluscs. Here, using two elevenin receptors in annelid Platynereis dumerilii, we found three putative elevenin GPCRs in Aplysia. We cloned the three receptors and tentatively named them apElevR1, apElevR2, and apElevR3. Using an inositol monophosphate (IP1) accumulation assay, we demonstrated that Aplysia elevenin with the disulfide bond activated the three putative receptors with low EC50 values (ranging from 1.2 to 25 nM), supporting that they are true receptors for elevenin. In contrast, elevenin without the disulfide bond could not activate the receptors, indicating that the disulfide bond is required for receptor activity. Using alanine substitution of individual conserved residues other than the two cysteines, we showed that these residues appear to be critical to receptor activity, and the three different receptors had different sensitivities to the single residue substitution. Finally, we examined the roles of those residues outside the disulfide bond ring by removing these residues and found that they also appeared to be important to receptor activity. Thus, our study provides an important basis for further study of the functions of elevenin and its receptors in Aplysia and other molluscs.

Characterization of an Aplysia vasotocin signaling system and actions of posttranslational modifications and individual residues of the ligand on receptor activity

The vasopressin/oxytocin signaling system is present in both protostomes and deuterostomes and plays various physiological roles. Although there were reports for both vasopressin-like peptides and receptors in mollusc Lymnaea and Octopus, no precursor or receptors have been described in mollusc Aplysia. Here, through bioinformatics, molecular and cellular biology, we identified both the precursor and two receptors for Aplysia vasopressin-like peptide, which we named Aplysia vasotocin (apVT). The precursor provides evidence for the exact sequence of apVT, which is identical to conopressin G from cone snail venom, and contains 9 amino acids, with two cysteines at position 1 and 6, similar to nearly all vasopressin-like peptides. Through inositol monophosphate (IP1) accumulation assay, we demonstrated that two of the three putative receptors we cloned from Aplysia cDNA are true receptors for apVT. We named the two receptors as apVTR1 and apVTR2. We then determined the roles of post-translational modifications (PTMs) of apVT, i.e., the disulfide bond between two cysteines and the C-terminal amidation on receptor activity. Both the disulfide bond and amidation were critical for the activation of the two receptors. Cross-activity with conopressin S, annetocin from an annelid, and vertebrate oxytocin showed that although all three ligands can activate both receptors, the potency of these peptides differed depending on their residue variations from apVT. We, therefore, tested the roles of each residue through alanine substitution and found that each substitution could reduce the potency of the peptide analog, and substitution of the residues within the disulfide bond tended to have a larger impact on receptor activity than the substitution of those outside the bond. Moreover, the two receptors had different sensitivities to the PTMs and single residue substitutions. Thus, we have characterized the Aplysia vasotocin signaling system and showed how the PTMs and individual residues in the ligand contributed to receptor activity.

Endogenous l- to d-amino acid residue isomerization modulates selectivity between distinct neuropeptide receptor family members

The l- to d-amino acid residue isomerization of neuropeptides is an understudied post-translational modification found in animals across several phyla. Despite its physiological importance, little information is available regarding the impact of endogenous peptide isomerization on receptor recognition and activation. As a result, the full roles peptide isomerization play in biology are not well understood. Here, we identify that the Aplysia allatotropin-related peptide (ATRP) signaling system utilizes l- to d-residue isomerization of one amino acid residue in the neuropeptide ligand to modulate selectivity between two distinct G protein-coupled receptors (GPCRs). We first identified a novel receptor for ATRP that is selective for the D2-ATRP form, which bears a single d-phenylalanine residue at position 2. Using cell-based receptor activation experiments, we then characterized the stereoselectivity of the two known ATRP receptors for both endogenous ATRP diastereomers, as well as for homologous toxin peptides from a carnivorous predator. We found that the ATRP system displayed dual signaling through both the Gαq and Gαs pathways, and each receptor was selectively activated by one naturally occurring ligand diastereomer over the other. Overall, our results provide insights into an unexplored mechanism by which nature regulates intercellular communication. Given the challenges in detecting l- to d-residue isomerization from complex mixtures de novo and in identifying receptors for novel neuropeptides, it is likely that other neuropeptide-receptor systems may also utilize changes in stereochemistry to modulate receptor selectivity in a manner similar to that discovered here.

Cone snail species off the Brazilian coast and their venoms: a review and update

The genus Conus includes over 900 species of marine invertebrates known as cone snails, whose venoms are among the most powerful described so far. This potency is mainly due to the concerted action of hundreds of small bioactive peptides named conopeptides, which target different ion channels and membrane receptors and thus interfere with crucial physiological processes. By swiftly harpooning and injecting their prey and predators with such deadly cocktails, the slow-moving cone snails guarantee their survival in the harsh, competitive marine environment. Each cone snail species produces a unique venom, as the mature sequences of conopeptides from the venoms of different species share very little identity. This biochemical diversity, added to the numerous species and conopeptides contained in their venoms, results in an immense biotechnological and therapeutic potential, still largely unexplored. That is especially true regarding the bioprospection of the venoms of cone snail species found off the Brazilian coast - a region widely known for its biodiversity. Of the 31 species described in this region so far, only four - Conus cancellatus, Conus regius, Conus villepinii, and Conus ermineus - have had their venoms partially characterized, and, although many bioactive molecules have been identified, only a few have been actually isolated and studied. In addition to providing an overview on all the cone snail species found off the Brazilian coast to date, this review compiles the information on the structural and pharmacological features of conopeptides and other molecules identified in the venoms of the four aforementioned species, paving the way for future studies.

Characterisation of Elevenin-Vc1 from the Venom of Conus victoriae: A Structural Analogue of α-Conotoxins

Elevenins are peptides found in a range of organisms, including arthropods, annelids, nematodes, and molluscs. They consist of 17 to 19 amino acid residues with a single conserved disulfide bond. The subject of this study, elevenin-Vc1, was first identified in the venom of the cone snail Conus victoriae (Gen. Comp. Endocrinol. 2017, 244, 11-18). Although numerous elevenin sequences have been reported, their physiological function is unclear, and no structural information is available. Upon intracranial injection in mice, elevenin-Vc1 induced hyperactivity at doses of 5 or 10 nmol. The structure of elevenin-Vc1, determined using nuclear magnetic resonance spectroscopy, consists of a short helix and a bend region stabilised by the single disulfide bond. The elevenin-Vc1 structural fold is similar to that of α-conotoxins such as α-RgIA and α-ImI, which are also found in the venoms of cone snails and are antagonists at specific subtypes of nicotinic acetylcholine receptors (nAChRs). In an attempt to mimic the functional motif, Asp-Pro-Arg, of α-RgIA and α-ImI, we synthesised an analogue, designated elevenin-Vc1-DPR. However, neither elevenin-Vc1 nor the analogue was active at six different human nAChR subtypes (α1β1εδ, α3β2, α3β4, α4β2, α7, and α9α10) at 1 µM concentrations.

Structural models of viral insulin-like peptides and their analogs

The insulin receptor (IR), the insulin-like growth factor-1 receptor (IGF1R), and the insulin/IGF1 hybrid receptors (hybR) are homologous transmembrane receptors. The peptide ligands, insulin and IGF1, exhibit significant structural homology and can bind to each receptor via site-1 and site-2 residues with distinct affinities. The variants of the Iridoviridae virus family show capability in expressing single-chain insulin/IGF1 like proteins, termed viral insulin-like peptides (VILPs), which can stimulate receptors from the insulin family. The sequences of VILPs lacking the central C-domain (dcVILPs) are known, but their structures in unbound and receptor-bound states have not been resolved to date. We report all-atom structural models of three dcVILPs (dcGIV, dcSGIV, and dcLCDV1) and their complexes with the receptors (μIR, μIGF1R, and μhybR), and probed the peptide/receptor interactions in each system using all-atom molecular dynamics (MD) simulations. Based on the nonbonded interaction energies computed between each residue of peptides (insulin and dcVILPs) and the receptors, we provide details on residues establishing significant interactions. The observed site-1 insulin/μIR interactions are consistent with previous experimental studies, and a residue-level comparison of interactions of peptides (insulin and dcVILPs) with the receptors revealed that, due to sequence differences, dcVILPs also establish some interactions distinct from those between insulin and IR. We also designed insulin analogs and report enhanced interactions between some analogs and the receptors.

Venomics of the Central European Myrmicine Ants Myrmica rubra and Myrmica ruginodis

Animal venoms are a rich source of novel biomolecules with potential applications in medicine and agriculture. Ants are one of the most species-rich lineages of venomous animals. However, only a fraction of their biodiversity has been studied so far. Here, we investigated the venom components of two myrmicine (subfamily Myrmicinae) ants: Myrmica rubra and Myrmica ruginodis. We applied a venomics workflow based on proteotranscriptomics and found that the venoms of both species are composed of several protein classes, including venom serine proteases, cysteine-rich secretory protein, antigen 5 and pathogenesis-related 1 (CAP) superfamily proteins, Kunitz-type serine protease inhibitors and venom acid phosphatases. Several of these protein classes are known venom allergens, and for the first time we detected phospholipase A1 in the venom of M. ruginodis. We also identified two novel epidermal growth factor (EGF) family toxins in the M. ruginodis venom proteome and an array of additional EGF-like toxins in the venom gland transcriptomes of both species. These are similar to known toxins from the related myrmicine ant, Manica rubida, and the myrmecine (subfamily Myrmeciinae) Australian red bulldog ant Myrmecia gullosa, and are possibly deployed as weapons in defensive scenarios or to subdue prey. Our work suggests that M.rubra and M. ruginodis venoms contain many enzymes and other high-molecular-weight proteins that cause cell damage. Nevertheless, the presence of EGF-like toxins suggests that myrmicine ants have also recruited smaller peptide components into their venom arsenal. Although little is known about the bioactivity and function of EGF-like toxins, their presence in myrmicine and myrmecine ants suggests they play a key role in the venom systems of the superfamily Formicoidea. Our work adds to the emerging picture of ant venoms as a source of novel bioactive molecules and highlights the need to incorporate such taxa in future venom bioprospecting programs.

Evolution, expression patterns and distribution of novel ribbon worm predatory and defensive toxins

Ribbon worms are active predators that use an eversible proboscis to inject venom into their prey and defend themselves with toxic epidermal secretions. Previous work on nemertean venom has largely focused on just a few species and has not investigated the different predatory and defensive secretions in detail. Consequently, our understanding of the composition and evolution of ribbon worm venoms is still very limited. Here, we present a comparative study of nemertean venom combining RNA-seq differential gene expression analyses of venom-producing tissues, tandem mass spectrometry-based proteomics of toxic secretions, and mass spectrometry imaging of proboscis sections, to shed light onto the composition and evolution of predatory and defensive toxic secretions in Antarctonemertes valida. Our analyses reveal a wide diversity of putative defensive and predatory toxins with tissue-specific gene expression patterns and restricted distributions to the mucus and proboscis proteomes respectively, suggesting that ribbon worms produce distinct toxin cocktails for predation and defense. Our results also highlight the presence of numerous lineage-specific toxins, indicating that venom evolution is highly divergent across nemerteans, producing toxin cocktails that might be finely tuned to subdue different prey. Our data also suggest that the hoplonemertean proboscis is a highly specialized predatory organ that seems to be involved in a variety of biological functions besides predation, including secretion and sensory perception. Overall, our results advance our knowledge into the diversity and evolution of nemertean venoms and highlight the importance of combining different types of data to characterize toxin composition in understudied venomous organisms.

Structures and interactions of insulin-like peptides from cone snail venom

The venomous insulin-like peptides released by certain cone snails stimulate hypoglycemic shock to immobilize fish and catch the prey. Compared to human insulin (hIns), the cone snail insulins (Con-Ins) are typically monomeric and shorter in sequence, yet they exhibit moderate hIns-like biological activity. We have modeled six variants of Con-Ins (G3, K1, K2, T1A, T1B, and T2) and carried out explicit-solvent molecular dynamics (MD) simulations of eight types of insulins, two with known structures (hIns and Con-Ins-G1) and six Con-Ins with modeled structures, to characterize key residues of each insulin that interact with the truncated human insulin receptor (μIR). We show that each insulin/μIR complex is stable during explicit-solvent MD simulations and hIns interactions indicate the highest affinity for the "site 1" of IR. The residue contact maps reveal that each insulin preferably interacts with the αCT peptide than the L1 domain of IR. Through analysis of the average nonbonded interaction energy contribution of every residue of each insulin for the μIR, we probe the residues establishing favorable interactions with the receptor. We compared the interaction energy of each residue of every Con-Ins to the μIR and observed that γ-carboxylated glutamate (Gla), His, Thr, Tyr, Tyr/His, and Asn in Con-Ins are favorable substitutions for GluA4, AsnA21, ValB12, LeuB15, GlyB20, and ArgB22 in hIns, respectively. The identified insulin analogs, although lacking the last eight residues of the B-chain of hIns, bind strongly to μIR. Our findings are potentially useful in designing potent fast-acting therapeutic insulin.

Comparative Venomics of the Cryptic Cone Snail Species Virroconus ebraeus and Virroconus judaeus

The venom duct transcriptomes and proteomes of the cryptic cone snail species Virroconus ebraeus and Virroconus judaeus were obtained and compared. The most abundant and shared conotoxin precursor superfamilies in both species were M, O1, and O2. Additionally, three new putative conotoxin precursor superfamilies (Virro01-03) with cysteine pattern types VI/VII and XVI were identified. The most expressed conotoxin precursor superfamilies were SF-mi2 and M in V. ebraeus, and Cerm03 and M in V. judaeus. Up to 16 conotoxin precursor superfamilies and hormones were differentially expressed between both species, and clustered into two distinct sets, which could represent adaptations of each species to different diets. Finally, we predicted, with machine learning algorithms, the 3D structure model of selected venom proteins including the differentially expressed Cerm03 and SF-mi2, an insulin type 3, a Gastridium geographus GVIA-like conotoxin, and an ortholog to the Pionoconus magus ω-conotoxin MVIIA (Ziconotide).

Bioactive Peptides: Synthesis, Sources, Applications, and Proposed Mechanisms of Action

Bioactive peptides are a group of biological molecules that are normally buried in the structure of parent proteins and become active after the cleavage of the proteins. Another group of peptides is actively produced and found in many microorganisms and the body of organisms. Today, many groups of bioactive peptides have been marketed chemically or recombinantly. This article reviews the various production methods and sources of these important/ubiquitous and useful biomolecules. Their applications, such as antimicrobial, antihypertensive, antioxidant activities, blood-lipid-lowering effect, opioid role, antiobesity, ability to bind minerals, antidiabetic, and antiaging effects, will be explored. The types of pathways proposed for bioactive applications will be in the next part of the article, and at the end, the future perspectives of bioactive peptides will be reviewed. Reading this article is recommended for researchers interested in various fields of physiology, microbiology, biochemistry, and nanotechnology and food industry professionals.

Regional expression of neuropeptides in the retina of the terrestrial slug Limax valentianus (Gastropoda, Stylommatophora, Limacidae)

Gastropods use lens-bearing eyes to detect ambient light. The retina contains photoreceptors that directly project to the brain. Here we identified the neurotransmitters that the retinal cells use for projection to the brain in the terrestrial slug Limax. We identified 12 genes encoding neuropeptides as well as a novel vesicular glutamate transporter, a marker of glutamatergic neuron, expressed in the retinal cells. Spatial expression profiles of the neuropeptide genes were determined by in situ hybridization. WWamide/MIP1/Pedal peptide2 were co-expressed in the neurons of the accessory retina. In the main retina, prohormone-4 was expressed in the ventro-lateral region. Clionin was expressed in the ventro-medial region. Pedal peptide was expressed in the anterior region of the main retina and in the accessory retina. Enterin was expressed in many neurons, including the accessory retina, but not in the dorsal region. FxRIamide1 and 2 were co-expressed in the posterior region. Prohormone-4 variant was uniformly expressed in many neurons but scarcely in the accessory retina. MIP2 was widely expressed throughout the dorso-ventral axis in the posterio-lateral region of the main retina. Myo1 was expressed in many neurons of the main retina but predominantly in the dorsal region. These expression patterns were confirmed by immunohistochemistry with specific antibodies against the neuropeptides. Projections of these peptidergic retinal neurons were confirmed by immunostaining of the optic nerve. Our present study revealed regional differentiation of the retina with respect to the neurotransmitters that the retinal cells use. neuropeptides, retina, neurotransmitter, gastropod, Lehmannia This article is protected by copyright. All rights reserved.

A drug discovery approach based on comparative transcriptomics between two toxin-secreting marine annelids: Glycera alba and Hediste diversicolor

While Glycera alba secretes neurotoxins, Hediste diversicolor may secrete fewer toxins with a broader action. Transcriptomics and human interactome-directed analysis unraveled promising candidates for biomedical applications from either annelid.

A Combined Transcriptomics and Proteomics Approach Reveals the Differences in the Predatory and Defensive Venoms of the Molluscivorous Cone Snail Cylinder ammiralis (Caenogastropoda: Conidae)

Venoms are complex mixtures of proteins that have evolved repeatedly in the animal kingdom. Cone snail venoms represent one of the best studied venom systems. In nature, this venom can be dynamically adjusted depending on its final purpose, whether to deter predators or hunt prey. Here, the transcriptome of the venom gland and the proteomes of the predation-evoked and defensive venoms of the molluscivorous cone snail Cylinder ammiralis were catalogued. A total of 242 venom-related transcripts were annotated. The conotoxin superfamilies presenting more different peptides were O1, O2, T, and M, which also showed high expression levels (except T). The three precursors of the J superfamily were also highly expressed. The predation-evoked and defensive venoms showed a markedly distinct profile. A total of 217 different peptides were identified, with half of them being unique to one venom. A total of 59 peptides ascribed to 23 different protein families were found to be exclusive to the predatory venom, including the cono-insulin, which was, for the first time, identified in an injected venom. A total of 43 peptides from 20 protein families were exclusive to the defensive venom. Finally, comparisons of the relative abundance (in terms of number of peptides) of the different conotoxin precursor superfamilies showed that most of them present similar abundance regardless of the diet.

Transcriptome Profiling of the Pacific Oyster Crassostrea gigas Visceral Ganglia over a Reproduction Cycle Identifies Novel Regulatory Peptides

The neuropeptides involved in the regulation of reproduction in the Pacific oyster (Crassostrea gigas) are quite diverse. To investigate this diversity, a transcriptomic survey of the visceral ganglia (VG) was carried out over an annual reproductive cycle. RNA-seq data from 26 samples corresponding to VG at different stages of reproduction were de novo assembled to generate a specific reference transcriptome of the oyster nervous system and used to identify differentially expressed transcripts. Transcriptome mining led to the identification of novel neuropeptide precursors (NPPs) related to the bilaterian Eclosion Hormone (EH), crustacean female sex hormone/Interleukin 17, Nesfatin, neuroparsin/IGFBP, prokineticins, and urotensin I; to the protostome GNQQN, pleurin, prohormones 3 and 4, prothoracotropic hormones (PTTH), and QSamide/PXXXamide; to the lophotrochozoan CCWamide, CLCCY, HFAamide, and LXRX; and to the mollusk-specific NPPs CCCGS, clionin, FYFY, GNamide, GRWRN, GSWN, GWE, IWMPxxGYxx, LXRYamide, RTLFamide, SLRFamide, and WGAGamide. Among the complete repertoire of NPPs, no sex-biased expression was observed. However, 25 NPPs displayed reproduction stage-specific expression, supporting their involvement in the control of gametogenesis or associated metabolisms.

Nemertean, brachiopod and phoronid neuropeptidomics reveals ancestral spiralian signalling systems

Neuropeptides are diverse signaling molecules in animals commonly acting through G-protein coupled receptors (GPCRs). Neuropeptides and their receptors underwent extensive diversification in bilaterians and the relationships of many peptide–receptor systems have been clarified. However, we lack a detailed picture of neuropeptide evolution in lophotrochozoans as in-depth studies only exist for mollusks and annelids. Here, we analyze peptidergic systems in Nemertea, Brachiopoda, and Phoronida. We screened transcriptomes from 13 nemertean, 6 brachiopod, and 4 phoronid species for proneuropeptides and neuropeptide GPCRs. With mass spectrometry from the nemertean Lineus longissimus, we validated several predicted peptides and identified novel ones. Molecular phylogeny combined with peptide-sequence and gene-structure comparisons allowed us to comprehensively map spiralian neuropeptide evolution. We found most mollusk and annelid peptidergic systems also in nemerteans, brachiopods, and phoronids. We uncovered previously hidden relationships including the orthologies of spiralian CCWamides to arthropod agatoxin-like peptides and of mollusk APGWamides to RGWamides from annelids, with ortholog systems in nemerteans, brachiopods, and phoronids. We found that pleurin neuropeptides previously only found in mollusks are also present in nemerteans and brachiopods. We also identified cases of gene family duplications and losses. These include a protostome-specific expansion of RFamide/Wamide signaling, a spiralian expansion of GnRH-related peptides, and duplications of vasopressin/oxytocin before the divergence of brachiopods, phoronids, and nemerteans. This analysis expands our knowledge of peptidergic signaling in spiralians and other protostomes. Our annotated data set of nearly 1,300 proneuropeptide sequences and 600 GPCRs presents a useful resource for further studies of neuropeptide signaling.

Production, composition, and mode of action of the painful defensive venom produced by a limacodid caterpillar, Doratifera vulnerans

Venoms have evolved independently several times in Lepidoptera. Limacodidae is a family with worldwide distribution, many of which are venomous in the larval stage, but the composition and mode of action of their venom is unknown. Here, we use imaging technologies, transcriptomics, proteomics, and functional assays to provide a holistic picture of the venom system of a limacodid caterpillar, Doratifera vulnerans Contrary to dogma that defensive venoms are simple in composition, D. vulnerans produces a complex venom containing 151 proteinaceous toxins spanning 59 families, most of which are peptides <10 kDa. Three of the most abundant families of venom peptides (vulnericins) are 1) analogs of the adipokinetic hormone/corazonin-related neuropeptide, some of which are picomolar agonists of the endogenous insect receptor; 2) linear cationic peptides derived from cecropin, an insect innate immune peptide that kills bacteria and parasites by disrupting cell membranes; and 3) disulfide-rich knottins similar to those that dominate spider venoms. Using venom fractionation and a suite of synthetic venom peptides, we demonstrate that the cecropin-like peptides are responsible for the dominant pain effect observed in mammalian in vitro and in vivo nociception assays and therefore are likely to cause pain after natural envenomations by D. vulnerans Our data reveal convergent molecular evolution between limacodids, hymenopterans, and arachnids and demonstrate that lepidopteran venoms are an untapped source of novel bioactive peptides.

Small-molecule mimicry hunting strategy in the imperial cone snail, Conus imperialis

Venomous animals hunt using bioactive peptides, but relatively little is known about venom small molecules and the resulting complex hunting behaviors. Here, we explored the specialized metabolites from the venom of the worm-hunting cone snail, Conus imperialis Using the model polychaete worm Platynereis dumerilii, we demonstrate that C. imperialis venom contains small molecules that mimic natural polychaete mating pheromones, evoking the mating phenotype in worms. The specialized metabolites from different cone snails are species-specific and structurally diverse, suggesting that the cones may adopt many different prey-hunting strategies enabled by small molecules. Predators sometimes attract prey using the prey's own pheromones, in a strategy known as aggressive mimicry. Instead, C. imperialis uses metabolically stable mimics of those pheromones, indicating that, in biological mimicry, even the molecules themselves may be disguised, providing a twist on fake news in chemical ecology.

Hormone-like conopeptides - new tools for pharmaceutical design

Conopeptides are a diverse family of peptides found in the venoms of marine cone snails and are used in prey capture and host defence. Because of their potent activity on a range of mammalian targets they have attracted interest as leads in drug design. Until recently most focus had been on studying conopeptides having activity at ion channels and related neurological targets but, with recent discoveries that some conopeptides might play hormonal roles, a new area of conopeptide research has opened. In this article we first summarize the canonical pharmaceutical families of Conus venom peptides and then focus on new research relating to hormone-like conopeptides and their potential applications. Finally, we briefly examine methods of chemically stabilizing conopeptides to improve their pharmacological properties. A summary is presented of conopeptides in clinical trials and a call for future work on hormone-like conopeptides.

Neuropeptide signalling systems - An underexplored target for venom drug discovery

Neuropeptides are signalling molecules mainly secreted from neurons that act as neurotransmitters or peptide hormones to affect physiological processes and modulate behaviours. In humans, neuropeptides are implicated in numerous diseases and understanding their role in physiological processes and pathologies is important for therapeutic development. Teasing apart the (patho)physiology of neuropeptides remains difficult due to ligand and receptor promiscuity and the complexity of the signalling pathways. The current approach relies on a pharmacological toolbox of agonists and antagonists displaying high selectivity for independent receptor subtypes, with the caveat that only few selective ligands have been discovered or developed. Animal venoms represent an underexplored source for novel receptor subtype-selective ligands that could aid in dissecting human neuropeptide signalling systems. Multiple endogenous-like neuropeptides as well as peptides acting on neuropeptide receptors are present in venoms. In this review, we summarise current knowledge on neuropeptides and discuss venoms as a source for ligands targeting neuropeptide signalling systems.

Toxin-like neuropeptides in the sea anemone Nematostella unravel recruitment from the nervous system to venom

The sea anemone Nematostella vectensis (Anthozoa, Cnidaria) is a powerful model for characterizing the evolution of genes functioning in venom and nervous systems. Although venom has evolved independently numerous times in animals, the evolutionary origin of many toxins remains unknown. In this work, we pinpoint an ancestral gene giving rise to a new toxin and functionally characterize both genes in the same species. Thus, we report a case of protein recruitment from the cnidarian nervous to venom system. The ShK-like1 peptide has a ShKT cysteine motif, is lethal for fish larvae and packaged into nematocysts, the cnidarian venom-producing stinging capsules. Thus, ShK-like1 is a toxic venom component. Its paralog, ShK-like2, is a neuropeptide localized to neurons and is involved in development. Both peptides exhibit similarities in their functional activities: They provoke contraction in Nematostella polyps and are toxic to fish. Because ShK-like2 but not ShK-like1 is conserved throughout sea anemone phylogeny, we conclude that the two paralogs originated due to a Nematostella-specific duplication of a ShK-like2 ancestor, a neuropeptide-encoding gene, followed by diversification and partial functional specialization. ShK-like2 is represented by two gene isoforms controlled by alternative promoters conferring regulatory flexibility throughout development. Additionally, we characterized the expression patterns of four other peptides with structural similarities to studied venom components and revealed their unexpected neuronal localization. Thus, we employed genomics, transcriptomics, and functional approaches to reveal one venom component, five neuropeptides with two different cysteine motifs, and an evolutionary pathway from nervous to venom system in Cnidaria.

RgIA4 Accelerates Recovery from Paclitaxel-Induced Neuropathic Pain in Rats

Chemotherapeutic drugs are widely utilized in the treatment of human cancers. Painful chemotherapy-induced neuropathy is a common, debilitating, and dose-limiting side effect for which there is currently no effective treatment. Previous studies have demonstrated the potential utility of peptides from the marine snail from the genus Conus for the treatment of neuropathic pain. α-Conotoxin RgIA and a potent analog, RgIA4, have previously been shown to prevent the development of neuropathy resulting from the administration of oxaliplatin, a platinum-based antineoplastic drug. Here, we have examined its efficacy against paclitaxel, a chemotherapeutic drug that works by a mechanism of action distinct from that of oxaliplatin. Paclitaxel was administered at 2 mg/kg (intraperitoneally (IP)) every other day for a total of 8 mg/kg. Sprague Dawley rats that were co-administered RgIA4 at 80 µg/kg (subcutaneously (SC)) once daily, five times per week, for three weeks showed significant recovery from mechanical allodynia by day 31. Notably, the therapeutic effects reached significance 12 days after the last administration of RgIA4, which is suggestive of a rescue mechanism. These findings support the effects of RgIA4 in multiple chemotherapeutic models and the investigation of α9α10 nicotinic acetylcholine receptors (nAChRs) as a non-opioid target in the treatment of chronic pain.

Venom Diversity and Evolution in the Most Divergent Cone Snail Genus Profundiconus

Profundiconus is the most divergent cone snail genus and its unique phylogenetic position, sister to the rest of the family Conidae, makes it a key taxon for examining venom evolution and diversity. Venom gland and foot transcriptomes of Profundiconus cf. vaubani and Profundiconus neocaledonicus were de novo assembled, annotated, and analyzed for differential expression. One hundred and thirty-seven venom components were identified from P. cf. vaubani and 82 from P. neocaledonicus, with only four shared by both species. The majority of the transcript diversity was composed of putative peptides, including conotoxins, profunditoxins, turripeptides, insulin, and prohormone-4. However, there were also a significant percentage of other putative venom components such as chymotrypsin and L-rhamnose-binding lectin. The large majority of conotoxins appeared to be from new gene superfamilies, three of which are highly different from previously reported venom peptide toxins. Their low conotoxin diversity and the type of insulin found suggested that these species, for which no ecological information are available, have a worm or molluscan diet associated with a narrow dietary breadth. Our results indicate that Profundiconus venom is highly distinct from that of other cone snails, and therefore important for examining venom evolution in the Conidae family.

Conotoxins: Chemistry and Biology

The venom of the marine predatory cone snails (genus Conus) has evolved for prey capture and defense, providing the basis for survival and rapid diversification of the now estimated 750+ species. A typical Conus venom contains hundreds to thousands of bioactive peptides known as conotoxins. These mostly disulfide-rich and well-structured peptides act on a wide range of targets such as ion channels, G protein-coupled receptors, transporters, and enzymes. Conotoxins are of interest to neuroscientists as well as drug developers due to their exquisite potency and selectivity, not just against prey but also mammalian targets, thereby providing a rich source of molecular probes and therapeutic leads. The rise of integrated venomics has accelerated conotoxin discovery with now well over 10,000 conotoxin sequences published. However, their structural and pharmacological characterization lags considerably behind. In this review, we highlight the diversity of new conotoxins uncovered since 2014, their three-dimensional structures and folds, novel chemical approaches to their syntheses, and their value as pharmacological tools to unravel complex biology. Additionally, we discuss challenges and future directions for the field.

Conotoxin Diversity in the Venom Gland Transcriptome of the Magician's Cone, Pionoconus magus

The transcriptomes of the venom glands of two individuals of the magician’s cone, Pionoconus magus, from Okinawa (Japan) were sequenced, assembled, and annotated. In addition, RNA-seq raw reads available at the SRA database from one additional specimen of P. magus from the Philippines were also assembled and annotated. The total numbers of identified conotoxin precursors and hormones per specimen were 118, 112, and 93. The three individuals shared only five identical sequences whereas the two specimens from Okinawa had 30 sequences in common. The total number of distinct conotoxin precursors and hormones for P. magus was 275, and were assigned to 53 conotoxin precursor and hormone superfamilies, two of which were new based on their divergent signal region. The superfamilies that had the highest number of precursors were M (42), O1 (34), T (27), A (18), O2 (17), and F (13), accounting for 55% of the total diversity. The D superfamily, previously thought to be exclusive of vermivorous cones was found in P. magus and contained a highly divergent mature region. Similarly, the A superfamily alpha 4/3 was found in P. magus despite the fact that it was previously postulated to be almost exclusive of the genus Rhombiconus. Differential expression analyses of P. magus compared to Chelyconus ermineus, the only fish-hunting cone from the Atlantic Ocean revealed that M and A2 superfamilies appeared to be more expressed in the former whereas the O2 superfamily was more expressed in the latter.

Chemical synthesis of N-glycosylated insulin-like androgenic gland factor from the freshwater prawn Macrobrachium rosenbergii

Crustacean insulin-like androgenic gland factor (IAG) of Macrobrachium rosenbergii, a heterodimeric peptide having both four disulfide bonds and an N-linked glycan, was synthesized by the combination of solid-phase peptide synthesis and the regioselective disulfide formation reactions. The disulfide isomer of IAG could also be synthesized by the same manner. The conformational analysis of these peptides by circular dichroism (CD) spectral measurement indicated that the disulfide bond arrangement affected the peptide conformation in IAG. On the other hand, the N-linked glycan attached at A chain showed no effect on CD spectra of IAG. This is the first report for the chemical synthesis of insulin-like heterodimeric glycopeptide having three interchain disulfides, and the synthetic strategy shown here might be useful for the synthesis of other glycosylated four-disulfide insulin-like peptides.

Elevenin signaling modulates body color through the tyrosine-mediated cuticle melanism pathway

Elevenin is a newly discovered novel neuropeptide. Knockdown of either elevenin or orphan receptor NlA42 transcript expression by RNA interference caused severe cuticle melanization in the brown planthopper (BPH). Injection of a synthetic elevenin peptide not only rescued the body color phenotype in dselevenin-pretreated individuals but also suppressed melanization of black insects grown in natural conditions. Real-time quantitative PCR results revealed that elevenin expression levels were highest in the brain and salivary gland. Immunohistochemistry analysis confirmed that a precursor peptide of elevenin was generated in the salivary gland, suggesting that the salivary gland might be an important neurosecretory tissue in addition to the brain in BPH. Furthermore, double-strand RNA-mediated silencing of elevenin and NlA42 resulted in down-regulation of arylalkylamine-N-acetyltransferase and up-regulation of tyrosine hydroxylase, whereas elevenin peptide injection resulted in up-regulation of N-β-alanyldopamine synthase and aspartate 1-decarboxylase, indicating a complex regulation network for cuticle pigmentation. In addition, functional characterization demonstrated that NlA42 is a cognate receptor for elevenin, and couples to Gq and Gs proteins, triggering both PLC/Ca2+/PKC and AC/cAMP/PKA signaling pathways in response to elevenin treatment. These findings suggest that the elevenin signaling functions control BPH body color through the tyrosine-mediated cuticle melanism pathway.-Wang, S.-L., Wang, W.-W., Ma, Q., Shen, Z.-F., Zhang, M.-Q., Zhou, N.-M., Zhang, C.-X. Elevenin signaling modulates body color through the tyrosine-mediated cuticle melanism pathway.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Aplysia allatotropin-related peptide and its newly identified d-amino acid-containing epimer both activate a receptor and a neuronal target

l- to d-residue isomerization is a post-translational modification (PTM) present in neuropeptides, peptide hormones, and peptide toxins from several animals. In most cases, the d-residue is critical for the biological function of the resulting d-amino acid-containing peptide (DAACP). Here, we provide an example in native neuropeptides in which the DAACP and its all-l-amino acid epimer are both active at their newly identified receptor in vitro and at a neuronal target associated with feeding behavior. On the basis of sequence similarity to a known DAACP from cone snail venom, we hypothesized that allatotropin-related peptide (ATRP), a neuropeptide from the neuroscience model organism Aplysia californica, may form multiple diastereomers in the Aplysia central nervous system. We determined that ATRP exists as a d-amino acid-containing peptide (d2-ATRP) and identified a specific G protein-coupled receptor as an ATRP receptor. Interestingly, unlike many previously reported DAACPs and their all-l-residue analogs, both l-ATRP and d2-ATRP were potent agonists of this receptor and active in electrophysiological experiments. Finally, d2-ATRP was much more stable than its all-l-residue counterpart in Aplysia plasma, suggesting that in the case of ATRP, the primary role of the l- to d-residue isomerization may be to protect this peptide from aminopeptidase activity in the extracellular space. Our results indicate that l- to d-residue isomerization can occur even in an all-l-residue peptide with a known biological activity and that in some cases, this PTM may help modulate peptide signal lifetime in the extracellular space rather than activity at the cognate receptor.

Chemical synthesis of the crustacean insulin-like peptide with four disulfide bonds

Among the insulin-family peptides, two additional cysteine residues other than six conserved cysteines are sometimes found in invertebrate insulin-like peptides (ILPs), although the synthetic method for such four disulfide ILPs has not yet been well established. In this study, we synthesized a crustacean insulin-like androgenic gland factor with four disulfides by the regioselective disulfide bond formation reactions using four orthogonal Cys-protecting groups. Its disulfide isomer could be also synthesized by the same method, indicating that the synthetic strategy developed in this study might be useful for the synthesis of other four disulfide ILPs.

Conotoxin Diversity in Chelyconus ermineus (Born, 1778) and the Convergent Origin of Piscivory in the Atlantic and Indo-Pacific Cones

The transcriptome of the venom duct of the Atlantic piscivorous cone species Chelyconus ermineus (Born, 1778) was determined. The venom repertoire of this species includes at least 378 conotoxin precursors, which could be ascribed to 33 known and 22 new (unassigned) protein superfamilies, respectively. Most abundant superfamilies were T, W, O1, M, O2, and Z, accounting for 57% of all detected diversity. A total of three individuals were sequenced showing considerable intraspecific variation: each individual had many exclusive conotoxin precursors, and only 20% of all inferred mature peptides were common to all individuals. Three different regions (distal, medium, and proximal with respect to the venom bulb) of the venom duct were analyzed independently. Diversity (in terms of number of distinct members) of conotoxin precursor superfamilies increased toward the distal region whereas transcripts detected toward the proximal region showed higher expression levels. Only the superfamilies A and I3 showed statistically significant differential expression across regions of the venom duct. Sequences belonging to the alpha (motor cabal) and kappa (lightning-strike cabal) subfamilies of the superfamily A were mainly detected in the proximal region of the venom duct. The mature peptides of the alpha subfamily had the α4/4 cysteine spacing pattern, which has been shown to selectively target muscle nicotinic-acetylcholine receptors, ultimately producing paralysis. This function is performed by mature peptides having a α3/5 cysteine spacing pattern in piscivorous cone species from the Indo-Pacific region, thereby supporting a convergent evolution of piscivory in cones.

Shotgun Proteomics Analysis of Saliva and Salivary Gland Tissue from the Common Octopus Octopus vulgaris

The salivary apparatus of the common octopus ( Octopus vulgaris) has been the subject of biochemical study for over a century. A combination of bioassays, behavioral studies and molecular analysis on O. vulgaris and related species suggests that its proteome should contain a mixture of highly potent neurotoxins and degradative proteins. However, a lack of genomic and transcriptomic data has meant that the amino acid sequences of these proteins remain almost entirely unknown. To address this, we assembled the posterior salivary gland transcriptome of O. vulgaris and combined it with high resolution mass spectrometry data from the posterior and anterior salivary glands of two adults, the posterior salivary glands of six paralarvae and the saliva from a single adult. We identified a total of 2810 protein groups from across this range of salivary tissues and age classes, including 84 with homology to known venom protein families. Additionally, we found 21 short secreted cysteine rich protein groups of which 12 were specific to cephalopods. By combining protein expression data with phylogenetic analysis we demonstrate that serine proteases expanded dramatically within the cephalopod lineage and that cephalopod specific proteins are strongly associated with the salivary apparatus.

The role of thyrostimulin and its potential clinical significance

Thyrostimulin is a glycoprotein heterodimer of GPA2 and GPB5, first described in 2002. It is involved in the physiological function of several tissues. Moreover, evidence points towards the ability of thyrostimulin's individual monomers to induce a biological effect, which could denote the circulatory/systemic effects of the molecule when found in higher concentrations. From the evolutionary point of view, thyrostimulin shares a binding epitope with the thyroid-stimulating hormone for the thyroid stimulating hormone receptor, whilst possessing affinity for another unique binding site on the same receptor. Although thyrostimulin can be involved in the hypothalamicpituitary- thyroid axis, its presence in various tissues in an eclectic array of different species renders it multifunctional. From weight loss via increasing metabolic rate to progression of cancer in human ovaries, it is certainly not a signaling molecule to overlook. Furthermore, thyrostimulin has been implicated in bone metabolism, acute illness, and reproductive function. In summary, to our knowledge, this is the first review dealing with the physiological role of thyrostimulin and its potential applications in the clinical practice.