Insights into the origins of fish hunting in venomous cone snails from studies of Conus tessulatus

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.

Prey specificity of predatory venoms

Venom represents a key adaptation of many venomous predators, allowing them to immobilise prey quickly through chemical rather than physical warfare. Evolutionary arms races between prey and a predator are believed to be the main factor influencing the potency and composition of predatory venoms. Predators with narrowly restricted diets are expected to evolve specifically potent venom towards their focal prey, with lower efficacy on alternative prey. Here, we evaluate hypotheses on the evolution of prey-specific venom, focusing on the effect of restricted diet, prey defences, and prey resistance. Prey specificity as a potential evolutionary dead end is also discussed. We then provide an overview of the current knowledge on venom prey specificity, with emphasis on snakes, cone snails, and spiders. As the current evidence for venom prey specificity is still quite limited, we also overview the best approaches and methods for its investigation and provide a brief summary of potential model groups. Finally, possible applications of prey-specific toxins are discussed.

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.

Comparative Analysis of Alpha-1 Orthosteric-Site Binding by a Clade of Central American Pit Vipers (Genera Atropoides, Cerrophidion, Metlapilcoatlus, and Porthidium)

The distribution and relative potency of post-synaptic neurotoxic activity within Crotalinae venoms has been the subject of less investigation in comparison with Elapidae snake venoms. No previous studies have investigated post-synaptic neurotoxic activity within the Atropoides, Metlapilcoatlus, Cerrophidion, and Porthidium clade. Given the specificity of neurotoxins to relevant prey types, we aimed to uncover any activity present within this clade of snakes that may have been overlooked due to lower potency upon humans and thus not appearing as a clinical feature. Using biolayer interferometry, we assessed the relative binding of crude venoms to amphibian, lizard, bird, rodent and human α-1 nAChR orthosteric sites. We report potent alpha-1 orthosteric site binding in venoms from Atropoides picadoi, Metlapilcoatlus occiduus, M. olmec, M. mexicanus, M. nummifer. Lower levels of binding, but still notable, were evident for Cerrophidion godmani, C. tzotzilorum and C. wilsoni venoms. No activity was observed for Porthidium venoms, which is consistent with significant alpha-1 orthosteric site neurotoxicity being a trait that was amplified in the last common ancestor of Atropoides/Cerrophidion/Metlapilcoatlus subsequent to the split by Porthidium. We also observed potent taxon-selective activity, with strong selection for non-mammalian targets (amphibian, lizard, and bird). As these are poorly studied snakes, much of what is known about them is from clinical reports. The lack of affinity towards mammalian targets may explain the knowledge gap in neurotoxic activity within these species, since symptoms would not appear in bite reports. This study reports novel venom activity, which was previously unreported, indicating toxins that bind to post-synaptic receptors may be more widespread in pit vipers than previously considered. While these effects appear to not be clinically significant due to lineage-specific effects, they are of significant evolutionary novelty and of biodiscovery interest. This work sets the stage for future research directions, such as the use of in vitro and in vivo models to determine whether the alpha-1 orthosteric site binding observed within this study confers neurotoxic venom activity.

Coordinated adaptations define the ontogenetic shift from worm- to fish-hunting in a venomous cone snail

Marine cone snails have attracted researchers from all disciplines but early life stages have received limited attention due to difficulties accessing or rearing juvenile specimens. Here, we document the culture of Conus magus from eggs through metamorphosis to reveal dramatic shifts in predatory feeding behaviour between post-metamorphic juveniles and adult specimens. Adult C. magus capture fish using a set of paralytic venom peptides combined with a hooked radular tooth used to tether envenomed fish. In contrast, early juveniles feed exclusively on polychaete worms using a unique "sting-and-stalk" foraging behaviour facilitated by short, unbarbed radular teeth and a distinct venom repertoire that induces hypoactivity in prey. Our results demonstrate how coordinated morphological, behavioural and molecular changes facilitate the shift from worm- to fish-hunting in C. magus, and showcase juvenile cone snails as a rich and unexplored source of novel venom peptides for ecological, evolutionary and biodiscovery studies.

Historical Perspective of the Characterization of Conotoxins Targeting Voltage-Gated Sodium Channels

Marine toxins have potent actions on diverse sodium ion channels regulated by transmembrane voltage (voltage-gated ion channels) or by neurotransmitters (nicotinic acetylcholine receptor channels). Studies of these toxins have focused on varied aspects of venom peptides ranging from evolutionary relationships of predator and prey, biological actions on excitable tissues, potential application as pharmacological intervention in disease therapy, and as part of multiple experimental approaches towards an understanding of the atomistic characterization of ion channel structure. This review examines the historical perspective of the study of conotoxin peptides active on sodium channels gated by transmembrane voltage, which has led to recent advances in ion channel research made possible with the exploitation of the diversity of these marine toxins.

Principal Component and Structural Element Analysis Provide Insights into the Evolutionary Divergence of Conotoxins

Predatory cone snails (Conus) developed a sophisticated neuropharmacological mechanism to capture prey, escape against other predators, and deter competitors. Their venom's remarkable specificity for various ion channels and receptors is an evolutionary feat attributable to the venom's variety of peptide components (conotoxins). However, what caused conotoxin divergence remains unclear and may be related to the role of prey shift. Principal component analysis revealed clustering events within diet subgroups indicating peptide sequence similarity patterns based on the prey they subdue. Molecular analyses using multiple sequence alignment and structural element analysis were conducted to observe the events at the molecular level that caused the subgrouping. Three distinct subgroups were identified. Results showed homologous regions and conserved residues within diet subgroups but divergent between other groups. We specified that these structural elements caused subgrouping in alpha conotoxins that may play a role in function specificity. In each diet subgroup, amino acid character, length of intervening amino acids between cysteine residues, and polypeptide length influenced subgrouping. This study provides molecular insights into the role of prey shift, specifically diet preference, in conotoxin divergence.

Unconventional insulins from predators and pathogens

Insulin and its related peptides are found throughout the animal kingdom, in which they serve diverse functions. This includes regulation of glucose homeostasis, neuronal development and cognition. The surprising recent discovery that venomous snails evolved specialized insulins to capture fish demonstrated the nefarious use of this hormone in nature. Because of their streamlined role in predation, these repurposed insulins exhibit unique characteristics that have unraveled new aspects of the chemical ecology and structural biology of this important hormone. Recently, insulins were also reported in other venomous predators and pathogenic viruses, demonstrating the broader use of insulin by one organism to manipulate the physiology of another. In this Review, we provide an overview of the discovery and biomedical application of repurposed insulins and other hormones found in nature and highlight several unique insights gained from these unusual compounds.

Reconstructing the Origins of the Somatostatin and Allatostatin-C Signaling Systems Using the Accelerated Evolution of Biodiverse Cone Snail Toxins

Somatostatin and its related peptides (SSRPs) form an important family of hormones with diverse physiological roles. The ubiquitous presence of SSRPs in vertebrates and several invertebrate deuterostomes suggests an ancient origin of the SSRP signaling system. However, the existence of SSRP genes outside of deuterostomes has not been established, and the evolutionary history of this signaling system remains poorly understood. Our recent discovery of SSRP-like toxins (consomatins) in venomous marine cone snails (Conus) suggested the presence of a related signaling system in mollusks and potentially other protostomes. Here, we identify the molluscan SSRP-like signaling gene that gave rise to the consomatin family. Following recruitment into venom, consomatin genes experienced strong positive selection and repeated gene duplications resulting in the formation of a hyperdiverse family of venom peptides. Intriguingly, the largest number of consomatins was found in worm-hunting species (>400 sequences), indicating a homologous system in annelids, another large protostome phylum. Consistent with this, comprehensive sequence mining enabled the identification of SSRP-like sequences (and their corresponding orphan receptor) in annelids and several other protostome phyla. These results established the existence of SSRP-like peptides in many major branches of bilaterians and challenge the prevailing hypothesis that deuterostome SSRPs and protostome allatostatin-C are orthologous peptide families. Finally, having a large set of predator-prey SSRP sequences available, we show that although the cone snail's signaling SSRP-like genes are under purifying selection, the venom consomatin genes experience rapid directional selection to target receptors in a changing mix of prey.

Somatostatin venom analogs evolved by fish-hunting cone snails: From prey capture behavior to identifying drug leads

Somatostatin (SS) is a peptide hormone with diverse physiological roles. By investigating a deep-water clade of fish-hunting cone snails, we show that predator-prey evolution has generated a diverse set of SS analogs, each optimized to elicit specific systemic physiological effects in prey. The increased metabolic stability, distinct SS receptor activation profiles, and chemical diversity of the venom analogs make them suitable leads for therapeutic application, including pain, cancer, and endocrine disorders. Our findings not only establish the existence of SS-like peptides in animal venoms but also serve as a model for the synergy gained from combining molecular phylogenetics and behavioral observations to optimize the discovery of natural products with biomedical potential.

Venom duct origins of prey capture and defensive conotoxins in piscivorous Conus striatus

The venom duct origins of predatory and defensive venoms has not been studied for hook-and-line fish hunting cone snails despite the pharmacological importance of their venoms. To better understand the biochemistry and evolution of injected predatory and defensive venoms, we compared distal, central and proximal venom duct sections across three specimens of C. striatus (Pionoconus) using proteomic and transcriptomic approaches. A total of 370 conotoxin precursors were identified from the whole venom duct transcriptome. Milked defensive venom was enriched with a potent cocktail of proximally expressed inhibitory α-, ω- and μ-conotoxins compared to milked predatory venom. In contrast, excitatory κA-conotoxins dominated both the predatory and defensive venoms despite their distal expression, suggesting this class of conotoxin can be selectively expressed from the same duct segment in response to either a predatory or defensive stimuli. Given the high abundance of κA-conotoxins in the Pionoconus clade, we hypothesise that the κA-conotoxins have evolved through adaptive evolution following their repurposing from ancestral inhibitory A superfamily conotoxins to facilitate the dietary shift to fish hunting and species radiation in this clade.

The complete mitochondrial DNA genome of a cone snail, Conus betulinus (Neogastropoda: Conidae), from the South China sea

The complete mitochondrial genome of the tubular cone snail Conus betulinus is presented in this study. The C. betulinus mitochondrial genome was 16,240 bp with 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes, and a non-coding AT-rich region (D-loop). The overall base composition was estimated to be 25.67% for A, 38.26% for T, 21.38% for G, and 14.69% for C, with a high A + T content of 63.93%. Phylogenetic analyses based on 13 PCGs showed the close relationship of vermivorous C. betulinus with the common ancestor of molluscivorous Conus textile and Conus gloriamaris, providing a basis for further studies on the phylogenetics of cone snails according to their dietary type.

Non-Peptidic Small Molecule Components from Cone Snail Venoms

Venomous molluscs (Superfamily Conoidea) comprise a substantial fraction of tropical marine biodiversity (>15,000 species). Prior characterization of cone snail venoms established that bioactive venom components used to capture prey, defend against predators and for competitive interactions were relatively small, structured peptides (10–35 amino acids), most with multiple disulfide crosslinks. These venom components (“conotoxins, conopeptides”) have been widely studied in many laboratories, leading to pharmaceutical agents and probes. In this review, we describe how it has recently become clear that to varying degrees, cone snail venoms also contain bioactive non-peptidic small molecule components. Since the initial discovery of genuanine as the first bioactive venom small molecule with an unprecedented structure, a broad set of cone snail venoms have been examined for non-peptidic bioactive components. In particular, a basal clade of cone snails (Stephanoconus) that prey on polychaetes produce genuanine and many other small molecules in their venoms, suggesting that this lineage may be a rich source of non-peptidic cone snail venom natural products. In contrast to standing dogma in the field that peptide and proteins are predominantly used for prey capture in cone snails, these small molecules also contribute to prey capture and push the molecular diversity of cone snails beyond peptides. The compounds so far characterized are active on neurons and thus may potentially serve as leads for neuronal diseases. Thus, in analogy to the incredible pharmacopeia resulting from studying venom peptides, these small molecules may provide a new resource of pharmacological agents.

Discovery of a Potent Conorfamide from Conus episcopatus Using a Novel Zebrafish Larvae Assay

Natural products such as conotoxins have tremendous potential as tools for biomedical research and for the treatment of different human diseases. Conotoxins are peptides present in the venoms of predatory cone snails that have a rich diversity of pharmacological functions. One of the major bottlenecks in natural products research is the rapid identification and evaluation of bioactive molecules. To overcome this limitation, we designed a set of light-induced behavioral assays in zebrafish larvae to screen for bioactive conotoxins. We used this screening approach to test several unique conotoxins derived from different cone snail clades and discovered that a conorfamide from Conus episcopatus, CNF-Ep1, had the most dramatic alterations in the locomotor behavior of zebrafish larvae. Interestingly, CNF-Ep1 is also bioactive in several mouse assay systems when tested in vitro and in vivo. Our novel screening platform can thus accelerate the identification of bioactive marine natural products, and the first compound discovered using this assay has intriguing properties that may uncover novel neuronal circuitry.

Reticulate evolution in Conidae: Evidence of nuclear and mitochondrial introgression

Conidae is a hyperdiverse family of marine snails that has many hallmarks of adaptive radiation. Hybridization and introgression may contribute to such instances of rapid diversification by generating novel gene combinations that facilitate exploitation of distinct niches. Here we evaluated whether or not these mechanisms may have contributed to the evolutionary history of a subgenus of Conidae (Virroconus). Several observations hint at evidence of past introgression for members of this group, including incongruence between phylogenetic relationships inferred from mitochondrial gene sequences and morphology and widespread sympatry of many Virroconus species in the Indo-West Pacific. We generated and analyzed transcriptome data of Virroconus species to (i) infer a robust nuclear phylogeny, (ii) assess mitochondrial and nuclear gene tree discordance, and (iii) formally test for introgression of nuclear loci. We identified introgression of mitochondrial genomes and nuclear gene regions between ancestors of one pair of Virroconus species, and mitochondrial introgression between another pair. We also found evidence of adaptive introgression of conotoxin venom loci between a third pair of species. Together, our results demonstrate that hybridization and introgression impacted the evolutionary history of Virroconus and hence may have contributed to the adaptive radiation of Conidae.

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.

Identification of Conomarphin Variants in the Conus eburneus Venom and the Effect of Sequence and PTM Variations on Conomarphin Conformations

Marine cone snails belonging to the Conidae family make use of neuroactive peptides in their venom to capture prey. Here we report the proteome profile of the venom duct of Conus eburneus, a cone snail belonging to the Tesseliconus clade. Through tandem mass spectrometry and database searching against the C. eburneus transcriptome and the ConoServer database, we identified 24 unique conopeptide sequences in the venom duct. The majority of these peptides belong to the T and M gene superfamilies and are disulfide-bonded, with cysteine frameworks V, XIV, VI/VII, and III being the most abundant. All seven of the Cys-free peptides are conomarphin variants belonging to the M superfamily that eluted out as dominant peaks in the chromatogram. These conomarphins vary not only in amino acid residues in select positions along the backbone but also have one or more post-translational modifications (PTMs) such as proline hydroxylation, C-term amidation, and γ-carboxylation of glutamic acid. Using molecular dynamics simulations, the conomarphin variants were predicted to predominantly have hairpin-like or elongated structures in acidic pH. These two structures were found to have significant differences in electrostatic properties and the inclusion of PTMs seems to complement this disparity. The presence of polar PTMs (hydroxyproline and γ-carboxyglutamic acid) also appear to stabilize hydrogen bond networks in these conformations. Furthermore, these predicted structures are pH sensitive, becoming more spherical and compact at higher pH. The subtle conformational variations observed here might play an important role in the selection and binding of the peptides to their molecular targets.

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.

Characterization of the First Conotoxin from Conus ateralbus, a Vermivorous Cone Snail from the Cabo Verde Archipelago

Conus ateralbus is a cone snail endemic to the west side of the island of Sal, in the Cabo Verde Archipelago off West Africa. We describe the isolation and characterization of the first bioactive peptide from the venom of this species. This 30AA venom peptide is named conotoxin AtVIA (δ-conotoxin-like). An excitatory activity was manifested by the peptide on a majority of mouse lumbar dorsal root ganglion neurons. An analog of AtVIA with conservative changes on three amino acid residues at the C-terminal region was synthesized and this analog produced an identical effect on the mouse neurons. AtVIA has homology with δ-conotoxins from other worm-hunters, which include conserved sequence elements that are shared with δ-conotoxins from fish-hunting Conus. In contrast, there is no comparable sequence similarity with δ-conotoxins from the venoms of molluscivorous Conus species. A rationale for the potential presence of δ-conotoxins, that are potent in vertebrate systems in two different lineages of worm-hunting cone snails, is discussed.

High-Throughput Identification and Analysis of Novel Conotoxins from Three Vermivorous Cone Snails by Transcriptome Sequencing

The venom of each Conus species consists of a diverse array of neurophysiologically active peptides, which are mostly unique to the examined species. In this study, we performed high-throughput transcriptome sequencing to extract and analyze putative conotoxin transcripts from the venom ducts of 3 vermivorous cone snails (C. caracteristicus, C. generalis, and C. quercinus), which are resident in offshore waters of the South China Sea. In total, 118, 61, and 48 putative conotoxins (across 22 superfamilies) were identified from the 3 Conus species, respectively; most of them are novel, and some possess new cysteine patterns. Interestingly, a series of 45 unassigned conotoxins presented with a new framework of C-C-C-C-C-C, and their mature regions were sufficiently distinct from any other known conotoxins, most likely representing a new superfamily. O- and M-superfamily conotoxins were the most abundant in transcript number and transcription level, suggesting their critical roles in the venom functions of these vermivorous cone snails. In addition, we identified numerous functional proteins with potential involvement in the biosynthesis, modification, and delivery process of conotoxins, which may shed light on the fundamental mechanisms for the generation of these important conotoxins within the venom duct of cone snails.

Conodipine-P1-3, the First Phospholipases A2 Characterized from Injected Cone Snail Venom

The phospholipase A₂ (PLA₂s) superfamily are ubiquitous small enzymes that catalyze the hydrolysis of phospholipids at the sn-2 ester bond. PLA₂s in the venom of cone snails (conodipines, Cdpi) are composed of two chains termed as alpha and beta subunits. Conodipines are categorized within the group IX of PLA₂s. Here we describe the purification and biochemical characterization of three conodipines (Cdpi-P1, -P2 and -P3) isolated from the injected venom of Conus purpurascens Using proteomics methods, we determined the full sequences of all three conodipines. Conodipine-P1-3 have conserved consensus catalytic domain residues, including the Asp/His dyad. Additionally, these enzymes are expressed as a mixture of proline hydroxylated isoforms. The activities of the native Conodipine-Ps were evaluated by conventional colorimetric and by MS-based methods, which provide the first detailed cone snail venom conodipine activity monitored by mass spectrometry. Conodipines can have medicinal applications such inhibition of cancer proliferation, bacterial and viral infections among others.

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.

Novel analgesic ω-conotoxins from the vermivorous cone snail Conus moncuri provide new insights into the evolution of conopeptides

Cone snails are a diverse group of predatory marine invertebrates that deploy remarkably complex venoms to rapidly paralyse worm, mollusc or fish prey. ω-Conotoxins are neurotoxic peptides from cone snail venoms that inhibit Ca_v2.2 voltage-gated calcium channel, demonstrating potential for pain management via intrathecal (IT) administration. Here, we isolated and characterized two novel ω-conotoxins, MoVIA and MoVIB from Conus moncuri, the first to be identified in vermivorous (worm-hunting) cone snails. MoVIA and MoVIB potently inhibited human Ca_v2.2 in fluorimetric assays and rat Ca_v2.2 in patch clamp studies, and both potently displaced radiolabeled ω-conotoxin GVIA (¹²⁵I-GVIA) from human SH-SY5Y cells and fish brain membranes (IC₅₀ 2–9 pM). Intriguingly, an arginine at position 13 in MoVIA and MoVIB replaced the functionally critical tyrosine found in piscivorous ω-conotoxins. To investigate its role, we synthesized MoVIB-[R13Y] and MVIIA-[Y13R]. Interestingly, MVIIA-[Y13R] completely lost Ca_v2.2 activity and MoVIB-[R13Y] had reduced activity, indicating that Arg at position 13 was preferred in these vermivorous ω-conotoxins whereas tyrosine 13 is preferred in piscivorous ω-conotoxins. MoVIB reversed pain behavior in a rat neuropathic pain model, confirming that vermivorous cone snails are a new source of analgesic ω-conotoxins. Given vermivorous cone snails are ancestral to piscivorous species, our findings support the repurposing of defensive venom peptides in the evolution of piscivorous Conidae.

Mitochondrial genome sequencing of a vermivorous cone snail Conus quercinus supports the correlative analysis between phylogenetic relationships and dietary types of Conus species

Complete mitochondrial genome (mitogenome) sequence of a worm-hunting cone snail, Conus quercinus, was reported in this study. Its mitogenome, the longest one (16,460 bp) among reported Conus specie, is composed of 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes and one D-loop region. The mitochondrial gene arrangement is highly-conserved and identical to other reported. However, the D-loop region of C. quercinus is the longest (943 bp) with the higher A+T content (71.3%) and a long AT tandem repeat stretch (68 bp). Subsequent phylogenetic analysis demonstrated that three different dietary types (vermivorous, molluscivorous and piscivorous) of cone snails are clustered separately, suggesting that the phylogenetics of cone snails is related to their dietary types. In conclusion, our current work improves our understanding of the mitogenomic structure and evolutionary status of the vermivorous C. quercinus, which support the putative hypothesis that the Conus ancestor was vermivorous.

Pharmacology of predatory and defensive venom peptides in cone snails

Cone snails are predatory gastropods whose neurotoxic venom peptides (conotoxins) have been extensively studied for pharmacological probes, venom evolution mechanisms and potential therapeutics. Conotoxins have a wide range of structural and functional classes that continue to undergo accelerated evolution that underlies the rapid expansion of the genus over their short evolutionary history. A number of pharmacological classes, driven by separately evolved defensive and predatory venoms, have been hypothesised to facilitate shifts in prey that exemplify the adaptability of cone snails. Here we provide an overview of these pharmacological families and discuss their ecological roles and evolutionary impact.

Venomics-Accelerated Cone Snail Venom Peptide Discovery

Cone snail venoms are considered a treasure trove of bioactive peptides. Despite over 800 species of cone snails being known, each producing over 1000 venom peptides, only about 150 unique venom peptides are structurally and functionally characterized. To overcome the limitations of the traditional low-throughput bio-discovery approaches, multi-omics systems approaches have been introduced to accelerate venom peptide discovery and characterisation. This “venomic” approach is starting to unravel the full complexity of cone snail venoms and to provide new insights into their biology and evolution. The main challenge for venomics is the effective integration of transcriptomics, proteomics, and pharmacological data and the efficient analysis of big datasets. Novel database search tools and visualisation techniques are now being introduced that facilitate data exploration, with ongoing advances in related omics fields being expected to further enhance venomics studies. Despite these challenges and future opportunities, cone snail venomics has already exponentially expanded the number of novel venom peptide sequences identified from the species investigated, although most novel conotoxins remain to be pharmacologically characterised. Therefore, efficient high-throughput peptide production systems and/or banks of miniaturized discovery assays are required to overcome this bottleneck and thus enhance cone snail venom bioprospecting and accelerate the identification of novel drug leads.

Isolation, structural identification and biological characterization of two conopeptides from the Conus pennaceus venom

A novel anti-mollusk conopeptide pn4c was isolated from the Conus pennaceus venom by repeated HPLC fractionation based on the activity against freshwater snails. The primary structure of pn4c was determined by the mass spectrometric de novo sequencing analysis. In addition, pn3a was isolated from the same fraction containing pn4c, as a peptide with unknown functions.

Proteogenomics from a bioinformatics angle: A growing field

Proteogenomics is a research area that combines areas as proteomics and genomics in a multi-omics setup using both mass spectrometry and high-throughput sequencing technologies. Currently, the main goals of the field are to aid genome annotation or to unravel the proteome complexity. Mass spectrometry based identifications of matching or homologues peptides can further refine gene models. Also, the identification of novel proteoforms is also made possible based on detection of novel translation initiation sites (cognate or near-cognate), novel transcript isoforms, sequence variation or novel (small) open reading frames in intergenic or un-translated genic regions by analyzing high-throughput sequencing data from RNAseq or ribosome profiling experiments. Other proteogenomics studies using a combination of proteomics and genomics techniques focus on antibody sequencing, the identification of immunogenic peptides or venom peptides. Over the years, a growing amount of bioinformatics tools and databases became available to help streamlining these cross-omics studies. Some of these solutions only help in specific steps of the proteogenomics studies, e.g. building custom sequence databases (based on next generation sequencing output) for mass spectrometry fragmentation spectrum matching. Over the last few years a handful integrative tools also became available that can execute complete proteogenomics analyses. Some of these are presented as stand-alone solutions, whereas others are implemented in a web-based framework such as Galaxy. In this review we aimed at sketching a comprehensive overview of all the bioinformatics solutions that are available for this growing research area. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:584-599, 2017.

Linking neuroethology to the chemical biology of natural products: interactions between cone snails and their fish prey, a case study

From a biological perspective, a natural product can be defined as a compound evolved by an organism for chemical interactions with another organism including prey, predator, competitor, pathogen, symbiont or host. Natural products hold tremendous potential as drug leads and have been extensively studied by chemists and biochemists in the pharmaceutical industry. However, the biological purpose for which a natural product evolved is rarely addressed. By focusing on a well-studied group of natural products-venom components from predatory marine cone snails-this review provides a rationale for why a better understanding of the evolution, biology and biochemistry of natural products will facilitate both neuroscience and the potential for drug leads. The larger goal is to establish a new sub-discipline in the broader field of neuroethology that we refer to as "Chemical Neuroethology", linking the substantial work carried out by chemists on natural products with accelerating advances in neuroethology.

Coagulating Colubrids: Evolutionary, Pathophysiological and Biodiscovery Implications of Venom Variations between Boomslang (Dispholidus typus) and Twig Snake (Thelotornis mossambicanus)

Venoms can deleteriously affect any physiological system reachable by the bloodstream, including directly interfering with the coagulation cascade. Such coagulopathic toxins may be anticoagulants or procoagulants. Snake venoms are unique in their use of procoagulant toxins for predatory purposes. The boomslang (Dispholidus typus) and the twig snakes (Thelotornis species) are iconic African snakes belonging to the family Colubridae. Both species produce strikingly similar lethal procoagulant pathologies. Despite these similarities, antivenom is only produced for treating bites by D. typus, and the mechanisms of action of both venoms have been understudied. In this study, we investigated the venom of D. typus and T. mossambicanus utilising a range of proteomic and bioactivity approaches, including determining the procoagulant properties of both venoms in relation to the human coagulation pathways. In doing so, we developed a novel procoagulant assay, utilising a Stago STA-R Max analyser, to accurately detect real time clotting in plasma at varying concentrations of venom. This approach was used to assess the clotting capabilities of the two venoms both with and without calcium and phospholipid co-factors. We found that T. mossambicanus produced a significantly stronger coagulation response compared to D. typus. Functional enzyme assays showed that T. mossambicanus also exhibited a higher metalloprotease and phospholipase activity but had a much lower serine protease activity relative to D. typus venom. The neutralising capability of the available boomslang antivenom was also investigated on both species, with it being 11.3 times more effective upon D. typus venom than T. mossambicanus. In addition to being a faster clotting venom, T. mossambicanus was revealed to be a much more complex venom composition than D. typus. This is consistent with patterns seen for other snakes with venom complexity linked to dietary complexity. Consistent with the external morphological differences in head shape between the two species, CT and MRI analyses revealed significant internal structural differences in skull architecture and venom gland anatomy. This study increases our understanding of not only the biodiscovery potential of these medically important species but also increases our knowledge of the pathological relationship between venom and the human coagulation cascade.

The Snake with the Scorpion's Sting: Novel Three-Finger Toxin Sodium Channel Activators from the Venom of the Long-Glanded Blue Coral Snake (Calliophis bivirgatus)

Millions of years of evolution have fine-tuned the ability of venom peptides to rapidly incapacitate both prey and potential predators. Toxicofera reptiles are characterized by serous-secreting mandibular or maxillary glands with heightened levels of protein expression. These glands are the core anatomical components of the toxicoferan venom system, which exists in myriad points along an evolutionary continuum. Neofunctionalisation of toxins is facilitated by positive selection at functional hotspots on the ancestral protein and venom proteins have undergone dynamic diversification in helodermatid and varanid lizards as well as advanced snakes. A spectacular point on the venom system continuum is the long-glanded blue coral snake (Calliophis bivirgatus), a specialist feeder that preys on fast moving, venomous snakes which have both a high likelihood of prey escape but also represent significant danger to the predator itself. The maxillary venom glands of C. bivirgatus extend one quarter of the snake's body length and nestle within the rib cavity. Despite the snake's notoriety its venom has remained largely unstudied. Here we show that the venom uniquely produces spastic paralysis, in contrast to the flaccid paralysis typically produced by neurotoxic snake venoms. The toxin responsible, which we have called calliotoxin (δ-elapitoxin-Cb1a), is a three-finger toxin (3FTx). Calliotoxin shifts the voltage-dependence of NaV1.4 activation to more hyperpolarised potentials, inhibits inactivation, and produces large ramp currents, consistent with its profound effects on contractile force in an isolated skeletal muscle preparation. Voltage-gated sodium channels (NaV) are a particularly attractive pharmacological target as they are involved in almost all physiological processes including action potential generation and conduction. Accordingly, venom peptides that interfere with NaV function provide a key defensive and predatory advantage to a range of invertebrate venomous species including cone snails, scorpions, spiders, and anemones. Enhanced activation or delayed inactivation of sodium channels by toxins is associated with the extremely rapid onset of tetanic/excitatory paralysis in envenomed prey animals. A strong selection pressure exists for the evolution of such toxins where there is a high chance of prey escape. However, despite their prevalence in other venomous species, toxins causing delay of sodium channel inhibition have never previously been described in vertebrate venoms. Here we show that NaV modulators, convergent with those of invertebrates, have evolved in the venom of the long-glanded coral snake. Calliotoxin represents a functionally novel class of 3FTx and a structurally novel class of NaV toxins that will provide significant insights into the pharmacology and physiology of NaV. The toxin represents a remarkable case of functional convergence between invertebrate and vertebrate venom systems in response to similar selection pressures. These results underscore the dynamic evolution of the Toxicofera reptile system and reinforces the value of using evolution as a roadmap for biodiscovery.

Venom Peptides From Cone Snails: Pharmacological Probes for Voltage-Gated Sodium Channels

The venoms of cone snails provide a rich source of neuroactive peptides (conotoxins). Several venom peptide families have been identified that are either agonists (ι- and δ-conotoxins) or antagonists (μ- and μO-conotoxins) of voltage-gated sodium channels (VGSCs). Members of these conotoxin classes have been integral in identifying and characterizing specific neurotoxin binding sites on the channel. Furthermore, given the specificity of some of these peptides for one sodium channel subtype over another, conotoxins have also proven useful in exploring differences between VGSC subtypes. This chapter summarizes the current knowledge of the structure and function based on the results of conotoxin interactions with VGSCs and correlates the peptides with the phylogeny of the Conus species from which they were derived.

Dietary breadth is positively correlated with venom complexity in cone snails

BACKGROUND

Although diet is believed to be a major factor underlying the evolution of venom, few comparative studies examine both venom composition and diet across a radiation of venomous species. Cone snails within the family, Conidae, comprise more than 700 species of carnivorous marine snails that capture their prey by using a cocktail of venomous neurotoxins (conotoxins or conopeptides). Venom composition across species has been previously hypothesized to be shaped by (a) prey taxonomic class (i.e., worms, molluscs, or fish) and (b) dietary breadth. We tested these hypotheses under a comparative phylogenetic framework using ecological data from past studies in conjunction with venom duct transcriptomes sequenced from 12 phylogenetically disparate cone snail species, including 10 vermivores (worm-eating), one molluscivore, and one generalist.

RESULTS

We discovered 2223 unique conotoxin precursor peptides that encoded 1864 unique mature toxins across all species, >90 % of which are new to this study. In addition, we identified two novel gene superfamilies and 16 novel cysteine frameworks. Each species exhibited unique venom profiles, with venom composition and expression patterns among species dominated by a restricted set of gene superfamilies and mature toxins. In contrast with the dominant paradigm for interpreting Conidae venom evolution, prey taxonomic class did not predict venom composition patterns among species. We also found a significant positive relationship between dietary breadth and measures of conotoxin complexity.

CONCLUSIONS

The poor performance of prey taxonomic class in predicting venom components suggests that cone snails have either evolved species-specific expression patterns likely as a consequence of the rapid evolution of conotoxin genes, or that traditional means of categorizing prey type (i.e., worms, mollusc, or fish) and conotoxins (i.e., by gene superfamily) do not accurately encapsulate evolutionary dynamics between diet and venom composition. We also show that species with more generalized diets tend to have more complex venoms and utilize a greater number of venom genes for prey capture. Whether this increased gene diversity confers an increased capacity for evolutionary change remains to be tested. Overall, our results corroborate the key role of diet in influencing patterns of venom evolution in cone snails and other venomous radiations.

δ-Conotoxin SuVIA suggests an evolutionary link between ancestral predator defence and the origin of fish-hunting behaviour in carnivorous cone snails

Some venomous cone snails feed on small fishes using an immobilizing combination of synergistic venom peptides that target Kv and Nav channels. As part of this envenomation strategy, δ-conotoxins are potent ichtyotoxins that enhance Nav channel function. δ-Conotoxins belong to an ancient and widely distributed gene superfamily, but any evolutionary link from ancestral worm-eating cone snails to modern piscivorous species has not been elucidated. Here, we report the discovery of SuVIA, a potent vertebrate-active δ-conotoxin characterized from a vermivorous cone snail (Conus suturatus). SuVIA is equipotent at hNaV1.3, hNaV1.4 and hNaV1.6 with EC50s in the low nanomolar range. SuVIA also increased peak hNaV1.7 current by approximately 75% and shifted the voltage-dependence of activation to more hyperpolarized potentials from -15 mV to -25 mV, with little effect on the voltage-dependence of inactivation. Interestingly, the proximal venom gland expression and pain-inducing effect of SuVIA in mammals suggest that δ-conotoxins in vermivorous cone snails play a defensive role against higher order vertebrates. We propose that δ-conotoxins originally evolved in ancestral vermivorous cones to defend against larger predators including fishes have been repurposed to facilitate a shift to piscivorous behaviour, suggesting an unexpected underlying mechanism for this remarkable evolutionary transition.

The first report on coagulation and phospholipase A2 activities of Persian Gulf lionfish, Pterois russelli, an Iranian venomous fish

Pterois russelli is a venomous fish belonging to scorpionidae family. Regarding to high significance value for tracing potential therapeutic molecules and special agents from venomous marine creatures, the present study was aimed to characterization of the Persian Gulf lionfish venom. Proteolytic, phospholipase, hemolytic, coagulation, edematogenic and dermonecrotic activities were determined for extracted venom. The LD50 of P. russelli venom was determined by intravenous injection in white Balb/c mice. Phospholipase A2 activity was recorded at 20 μg of total venom. Coagulation activity on human plasma was shown by Prothrombin Time (PT) and activated Partial Thromboplastin Time (APTT) assays and coagulation visualized after 7 and 14 s respectively for 60 μg of crude venom. LD50 was calculated as 10.5 mg/kg. SDS-PAGE revealed the presence of major and minor protein bands between 6 and 205 kDa. Different amounts of crude venom ranged from 1.87 to 30 μg showed proteolytic activity on casein. The highest edematic activity was detected at 20 μg. Our findings showed that the edematic activity was dose dependent and persisted for 48 h after injection. The crude venom did not induce dermonecrotic activity on rabbit skin and showed no hemolytic activity on human, mouse and rabbit erythrocytes. This is the first report for phospholipase A2 and coagulation activity in venomous fish and venomous marine animals respectively. Proteolytic activity of P. russelli venom is in accordance with the other genara of scorpionidae family. According to venom activity on intrinsic and extrinsic coagulation pathways, lionfish venom would be contained an interesting pharmaceutical agent. This study is pending to further characterization of phospholipase A2, coagulation, and protease activities and also in vivo activity on animal model of surface and internal bleeding.

Conotoxins That Could Provide Analgesia through Voltage Gated Sodium Channel Inhibition

Chronic pain creates a large socio-economic burden around the world. It is physically and mentally debilitating, and many sufferers are unresponsive to current therapeutics. Many drugs that provide pain relief have adverse side effects and addiction liabilities. Therefore, a great need has risen for alternative treatment strategies. One rich source of potential analgesic compounds that has emerged over the past few decades are conotoxins. These toxins are extremely diverse and display selective activity at ion channels. Voltage gated sodium (Na_V) channels are one such group of ion channels that play a significant role in multiple pain pathways. This review will explore the literature around conotoxins that bind Na_V channels and determine their analgesic potential.

Prey-Capture Strategies of Fish-Hunting Cone Snails: Behavior, Neurobiology and Evolution

The venomous fish-hunting cone snails (Conus) comprise eight distinct lineages evolved from ancestors that preyed on worms. In this article, we attempt to reconstruct events resulting in this shift in food resource by closely examining patterns of behavior, biochemical agents (toxins) that facilitate prey capture and the combinations of toxins present in extant species. The first sections introduce three different hunting behaviors associated with piscivory: 'taser-and-tether', 'net-engulfment' and 'strike-and-stalk'. The first two fish-hunting behaviors are clearly associated with distinct groups of venom components, called cabals, which act in concert to modify the behavior of prey in a specific manner. Derived fish-hunting behavior clearly also correlates with physical features of the radular tooth, the device that injects these biochemical components. Mapping behavior, biochemical components and radular tooth features onto phylogenetic trees shows that fish-hunting behavior emerged at least twice during evolution. The system presented here may be one of the best examples where diversity in structure, physiology and molecular features were initially driven by particular pathways selected through behavior.

Constellation pharmacology: a new paradigm for drug discovery

Constellation pharmacology is a cell-based high-content phenotypic-screening platform that utilizes subtype-selective pharmacological agents to elucidate the cell-specific combinations (constellations) of key signaling proteins that define specific cell types. Heterogeneous populations of native cells, in which the different individual cell types have been identified and characterized, are the foundation for this screening platform. Constellation pharmacology is useful for screening small molecules or for deconvoluting complex mixtures of biologically active natural products. This platform has been used to purify natural products and discover their molecular mechanisms. In the ongoing development of constellation pharmacology, there is a positive feedback loop between the pharmacological characterization of cell types and screening for new drug candidates. As constellation pharmacology is used to discover compounds with novel targeting-selectivity profiles, those new compounds then further help to elucidate the constellations of specific cell types, thereby increasing the content of this high-content platform.