Venom variation during prey capture by the cone snail, Conus textile

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.

Biomedical Potential of the Neglected Molluscivorous and Vermivorous Conus Species

Within the Conidae family, the piscivorous Conus species have been a hotspot target for drug discovery. Here, we assess the relevance of Conus and their other feeding habits, and thus under distinctive evolutionary constraints, to highlight the potential of neglected molluscivorous and vermivorous species in biomedical research and pharmaceutical industry. By singling out the areas with inadequate Conus disquisition, such as the Tamil Nadu Coast and the Andaman Islands, research resources can be expanded and better protected through awareness. In this study, 728 Conus species and 190 species from three other genera (1 from Californiconus, 159 from Conasprella and 30 from Profundiconus) in the Conidae family are assessed. The phylogenetic relationships of the Conidae species are determined and their known feeding habits superimposed. The worm-hunting species appeared first, and later the mollusc- and fish-hunting species were derived independently in the Neogene period (around 23 million years ago). Interestingly, many Conus species in the warm and shallow waters become polyphagous, allowing them to hunt both fish and worms, given the opportunities. Such newly gained trait is multi originated. This is controversial, given the traditional idea that most Conus species are specialized to hunt certain prey categories. However, it shows the functional complexity and great potential of conopeptides from some worm-eating species. Pharmaceutical attempts and relevant omics data have been differentially obtained. Indeed, data from the fish-hunting species receive strong preference over the worm-hunting ones. Expectedly, conopeptides from the fish-hunting species are believed to include the most potential candidates for biomedical research. Our work revisits major findings throughout the Conus evolution and emphasizes the importance of increasing omics surveys complemented with further behavior observation studies. Hence, we claim that Conus species and their feeding habits are equally important, highlighting many places left for Conus exploration worldwide. We also discuss the Conotoxin drug discovery potentials and the urgency of protecting the bioresources of Conus species. In particular, some vermivorous species have demonstrated great potential in malaria therapy, while other conotoxins from several worm- and mollusc-eating species exhibited explicit correlation with SARS-CoV-2. Reclaiming idle data with new perspectives could also promote interdisciplinary studies in both virological and toxicological fields.

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.

Proteogenomic Assessment of Intraspecific Venom Variability: Molecular Adaptations in the Venom Arsenal of Conus purpurascens

Cone snails produce venom that contains diverse groups of peptides (conopeptides/conotoxins) and display a wide mass range, high rate of posttranslational modifications, and many potential pharmacological targets. Here we employ a proteogenomic approach to maximize conopeptide identification from the injected venom of Conus purpurascens. mRNA sequences from C. purpurascens venom ducts were assembled into a search database and complemented with known sequences and de novo approaches. We used a top-down peptidomic approach and tandem mass spectrometry identification to compare injected venom samples of 27 specimens. This intraspecific analysis yielded 543 unique conopeptide identifications, which included 33 base conopeptides and their toxiforms, 21 of which are novel. The results reveal two distinct venom profiles with different synergistic interactions to effectively target neural pathways aimed to immobilize prey. These venom expression patterns will aid target prediction, a significant step toward developing conotoxins into valuable drugs or neural probes.

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We analyzed the injected venom of 27 specimens of Conus purpurascens.

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We found 543 unique conopeptide identifications.

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We identified 21 novel base conopeptides.

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We found two distinct venom profiles with different synergistic interactions.

Combined Proteotranscriptomic-Based Strategy to Discover Novel Antimicrobial Peptides from Cone Snails

Despite their impressive diversity and already broad therapeutic applications, cone snail venoms have received less attention as a natural source in the investigation of antimicrobial peptides than other venomous animals such as scorpions, spiders, or snakes. Cone snails are among the largest genera (Conus sp.) of marine invertebrates, with more than seven hundred species described to date. These predatory mollusks use their sophisticated venom apparatus to capture prey or defend themselves. In-depth studies of these venoms have unraveled many biologically active peptides with pharmacological properties of interest in the field of pain management, the treatment of epilepsy, neurodegenerative diseases, and cardiac ischemia. Considering sequencing efficiency and affordability, cone snail venom gland transcriptome analyses could allow the discovery of new, promising antimicrobial peptides. We first present here the need for novel compounds like antimicrobial peptides as a viable alternative to conventional antibiotics. Secondly, we review the current knowledge on cone snails as a source of antimicrobial peptides. Then, we present the current state of the art in analytical methods applied to crude or milked venom followed by how antibacterial activity assay can be implemented for fostering cone snail antimicrobial peptides studies. We also propose a new innovative profile Hidden Markov model-based approach to annotate full venom gland transcriptomes and speed up the discovery of potentially active peptides from cone snails.

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.

Comparative transcriptomics of the venoms of continental and insular radiations of West African cones

The transcriptomes of the venom glands of 13 closely related species of vermivorous cones endemic to West Africa from genera Africonus and Varioconus were sequenced and venom repertoires compared within a phylogenetic framework using one Kalloconus species as outgroup. The total number of conotoxin precursors per species varied between 108 and 221. Individuals of the same species shared about one-fourth of the total conotoxin precursors. The number of common sequences was drastically reduced in the pairwise comparisons between closely related species, and the phylogenetical signal was totally eroded at the inter-generic level (no sequence was identified as shared derived), due to the intrinsic high variability of these secreted peptides. A common set of four conotoxin precursor superfamilies (T, O1, O2 and M) was expanded in all studied cone species, and thus, they are considered the basic venom toolkit for hunting and defense in the West African vermivorous cone snails. Maximum-likelihood ancestral character reconstructions inferred shared conotoxin precursors preferentially at internal nodes close to the tips of the phylogeny (between individuals and between closely related species) as well as in the common ancestor of Varioconus. Besides the common toolkit, the two genera showed significantly distinct catalogues of conotoxin precursors in terms of type of superfamilies present and the abundance of members per superfamily, but had similar relative expression levels indicating functional convergence. Differential expression comparisons between vermivorous and piscivorous cones highlighted the importance of the A and S superfamilies for fish hunting and defense.

Characterising Functional Venom Profiles of Anthozoans and Medusozoans within Their Ecological Context

This review examines the current state of knowledge regarding toxins from anthozoans (sea anemones, coral, zoanthids, corallimorphs, sea pens and tube anemones). We provide an overview of venom from phylum Cnidaria and review the diversity of venom composition between the two major clades (Medusozoa and Anthozoa). We highlight that the functional and ecological context of venom has implications for the temporal and spatial expression of protein and peptide toxins within class Anthozoa. Understanding the nuances in the regulation of venom arsenals has been made possible by recent advances in analytical technologies that allow characterisation of the spatial distributions of toxins. Furthermore, anthozoans are unique in that ecological roles can be assigned using tissue expression data, thereby circumventing some of the challenges related to pharmacological screening.

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.

Evolutionary Ecology of Fish Venom: Adaptations and Consequences of Evolving a Venom System

Research on venomous animals has mainly focused on the molecular, biochemical, and pharmacological aspects of venom toxins. However, it is the relatively neglected broader study of evolutionary ecology that is crucial for understanding the biological relevance of venom systems. As fish have convergently evolved venom systems multiple times, it makes them ideal organisms to investigate the evolutionary ecology of venom on a broader scale. This review outlines what is known about how fish venom systems evolved as a result of natural enemy interactions and about the ecological consequences of evolving a venom system. This review will show how research on the evolutionary ecology of venom in fish can aid in understanding the evolutionary ecology of animal venoms more generally. Further, understanding these broad ecological questions can shed more light on the other areas of toxinology, with applications across multiple disciplinary fields.

Conus Envenomation of Humans: In Fact and Fiction

Prominent hallmarks of the widely distributed, mainly tropical marine snail genus Conus are: (1) its unusually high species diversity; it is the largest genus of animals in the sea, with more than 800 recognized species; and (2) its specialized feeding behavior of overcoming prey by injection with potent neurotoxic, paralytic venoms, and swallowing the victim whole. Including the first report of a human fatality from a Conus sting nearly 350 years ago, at least 141 human envenomations have been recorded, of which 36 were fatal. Most Conus species are quite specialized predators that can be classified in one of three major feeding guilds: they prey exclusively or nearly so on worms, primarily polychaete annelids, other gastropods, sometimes including other Conus species, or fishes. These differences are shown to relate to the severity of human envenomations, with the danger increasing generally in the order listed above and a strong likelihood that all of the known human fatalities may be attributable solely to the single piscivorous species C. geographus.

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.

Structural plasticity of mini-M conotoxins - expression of all mini-M subtypes by Conus regius

The mini-M conotoxins are peptidic scaffolds found in the venom of cones snails. These scaffolds are tightly folded structures held together by three disulfide bonds with a CC-C-C-CC arrangement (conotoxin framework III) and belong to the M Superfamily of conotoxins. Here, we describe mini-M conotoxins from the venom of Conus regius, a Western Atlantic worm-hunting cone snail species using transcriptomic and peptidomic analyses. These C. regius conotoxins belong to three different subtypes: M1, M2, and M3. The subtypes show little sequence homology, and their loop sizes (intercysteine amino acid chains) vary significantly. The mini-Ms isolated from dissected venom contains preferentially hydroxylated proline residues, thus augmenting the structural reach of this conotoxin class. Using 2D-NMR methods, we have determined the 3D structure of reg3b, an M2 subtype conotoxin, which shows a constrained multi-turn scaffold. The structural diversity found within mini-M conotoxin scaffolds of C. regius is indicative of structural hypervariability of the conotoxin M superfamily that is not seen in other superfamilies. These stable minimalistic scaffolds may be investigated for the development of engineered peptides for therapeutic applications.

DATABASES

Sequences are available in GenBank under accession numbers MF588935-MF588952. Structural data are available in the RCSB protein database under the accession code 6BX9.

Ecological venomics: How genomics, transcriptomics and proteomics can shed new light on the ecology and evolution of venom

Animal venom is a complex cocktail of bioactive chemicals that traditionally drew interest mostly from biochemists and pharmacologists. However, in recent years the evolutionary and ecological importance of venom is realized as this trait has direct and strong influence on interactions between species. Moreover, venom content can be modulated by environmental factors. Like many other fields of biology, venom research has been revolutionized in recent years by the introduction of systems biology approaches, i.e., genomics, transcriptomics and proteomics. The employment of these methods in venom research is known as 'venomics'. In this review we describe the history and recent advancements of venomics and discuss how they are employed in studying venom in general and in particular in the context of evolutionary ecology. We also discuss the pitfalls and challenges of venomics and what the future may hold for this emerging scientific field.

Intraspecific variations in Conus purpurascens injected venom using LC/MALDI-TOF-MS and LC-ESI-TripleTOF-MS

The venom of cone snails is composed of highly modified peptides (conopeptides) that target a variety of ion channels and receptors. The venom of these marine gastropods represents a largely untapped resource of bioactive compounds of potential pharmaceutical value. Here, we use a combination of bioanalytical techniques to uncover the extent of venom expression variability in Conus purpurascens, a fish-hunting cone snail species. The injected venom of nine specimens of C. purpurascens was separated by reversed-phase high-performance liquid chromatography (RP-HPLC), and fractions were analyzed using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) in parallel with liquid chromatography-electrospray ionization (LC-ESI)-TripleTOF-MS to compare standard analytical protocols used in preparative bioassay-guided fractionations with a deeper peptidomic analysis. Here, we show that C. purpurascens exhibits pronounced intraspecific venom variability. RP-HPLC fractionation followed by MALDI-TOF-MS analysis of the injected venom of these nine specimens identified 463 distinct masses, with none common to all specimens. Using LC-ESI-TripleTOF-MS, the injected venom of these nine specimens yielded a total of 5517 unique masses. We also compare the injected venom of two specimens with their corresponding dissected venom. We found 2566 and 1990 unique masses for the dissected venom compared to 941 and 1959 masses in their corresponding injected venom. Of these, 742 and 1004 masses overlapped between the dissected and injected venom, respectively. The results indicate that larger conopeptide libraries can be assessed by studying multiple individuals of a given cone snail species. This expanded library of conopeptides enhances the opportunities for discovery of molecular modulators with direct relevance to human therapeutics. Graphical Abstract The venom of cone snails are extraordinarily complex mixtures of highly modified peptides. Venom analysis requires separation through RP-HPLC followed by MALDI-TOF mass spectrometry or direct analysis using LC-ESI-TripleTOF-MS. Using these techniques, venom intraspecific variability and comparison between injected and dissected were assessed.

Production and packaging of a biological arsenal: evolution of centipede venoms under morphological constraint

Venom represents one of the most extreme manifestations of a chemical arms race. Venoms are complex biochemical arsenals, often containing hundreds to thousands of unique protein toxins. Despite their utility for prey capture, venoms are energetically expensive commodities, and consequently it is hypothesized that venom complexity is inversely related to the capacity of a venomous animal to physically subdue prey. Centipedes, one of the oldest yet least-studied venomous lineages, appear to defy this rule. Although scutigeromorph centipedes produce less complex venom than those secreted by scolopendrid centipedes, they appear to rely heavily on venom for prey capture. We show that the venom glands are large and well developed in both scutigerid and scolopendrid species, but that scutigerid forcipules lack the adaptations that allow scolopendrids to inflict physical damage on prey and predators. Moreover, we reveal that scolopendrid venom glands have evolved to accommodate a much larger number of secretory cells and, by using imaging mass spectrometry, we demonstrate that toxin production is heterogeneous across these secretory units. We propose that the differences in venom complexity between centipede orders are largely a result of morphological restrictions of the venom gland, and consequently there is a strong correlation between the morphological and biochemical complexity of this unique venom system. The current data add to the growing body of evidence that toxins are not expressed in a spatially homogenous manner within venom glands, and they suggest that the link between ecology and toxin evolution is more complex than previously thought.