Central to the discovery of neuroactive compounds produced by predatory marine snails of the superfamily Conoidea (cone snails, terebrids, and turrids) is identifying those species with a venom apparatus. Previous analyses of western Pacific terebrid specimens has shown that some Terebridae groups have secondarily lost their venom apparatus. In order to efficiently characterize terebrid toxins, it is essential to devise a key for identifying which species have a venom apparatus. The findings presented here integrate molecular phylogeny and the evolution of character traits to infer the presence or absence of the venom apparatus in the Terebridae. Using a combined dataset of 156 western and 33 eastern Pacific terebrid samples, a phylogenetic tree was constructed based on analyses of 16S, COI and 12S mitochondrial genes. The 33 eastern Pacific specimens analyzed represent four different species: Acus strigatus, Terebra argyosia, T. ornata, and T. cf. formosa. Anatomical analysis was congruent with molecular characters, confirming that species included in the clade Acus do not have a venom apparatus, while those in the clade Terebra do. Discovery of the association between terebrid molecular phylogeny and the occurrence of a venom apparatus provides a useful tool for effectively identifying the terebrid lineages that may be investigated for novel pharmacological active neurotoxins, enhancing conservation of this important resource, while providing supplementary information towards understanding terebrid evolutionary diversification.
The Terebridae are a diverse family of tropical and subtropical marine gastropods that use a complex and modular venom apparatus to produce toxins that capture polychaete and enteropneust preys. The complexity of the terebrid venom apparatus suggests that venom apparatus development in the Terebridae could be linked to the diversification of the group and can be analyzed within a molecular phylogenetic scaffold to better understand terebrid evolution. Presented here is a molecular phylogeny of 89 terebrid species belonging to 12 of the 15 currently accepted genera, based on Bayesian inference and Maximum Likelihood analyses of amplicons of 3 mitochondrial (COI, 16S and 12S) and one nuclear (28S) genes. The evolution of the anatomy of the terebrid venom apparatus was assessed by mapping traits of six related characters: proboscis, venom gland, odontophore, accessory proboscis structure, radula, and salivary glands. A novel result concerning terebrid phylogeny was the discovery of a previously unrecognized lineage, which includes species of Euterebra and Duplicaria. The non- monophyly of most terebrid genera analyzed indicates that the current genus-level classification of the group is plagued with homoplasy and requires further taxonomic investigations. Foregut anatomy in the family Terebridae reveals an inordinate diversity of features that covers the range of variability within the entire superfamily Conoidea, and that hypodermic radulae have likely evolved independently on at least three occasions. These findings illustrate that terebrid venom apparatus evolution is not perfunctory, and involves independent and numerous changes of central features in the foregut anatomy. The multiple emergence of hypodermic marginal radular teeth in terebrids are presumably associated with variable functionalities, suggesting that terebrids have adapted to dietary changes that may have resulted from predator-prey relationships. The anatomical and phylogenetic results presented serve as a starting point to advance investigations about the role of predator-prey interactions in the diversification of the Terebridae and the impact on their peptide toxins, which are promising bioactive compounds for biomedical research and therapeutic drug development.
character evolution; key innovations; predator-prey system; radula; teretoxins; toxins
Toxoglossate marine gastropods, traditionally assigned to the families Conidae, Terebridae, and Turridae, are one of the most populous animal groups that use venom to capture their prey. These marine animals are generally characterized by a venom apparatus that consists of a muscular venom bulb and a tubular venom gland. The toxoglossan radula, often compared with a hypodermic needle for its use as a conduit to inject toxins into prey, is considered a major anatomical breakthrough that assisted in the successful initial radiation of these animals in the Cretaceous and early Tertiary. The pharmacological success of toxins from cone snails has made this group a star among biochemists and neuroscientists, but very little is known about toxins from the other Toxoglossa, and the phylogeny of these families is largely in doubt. Here we report the first molecular phylogeny for the Terebridae and use the results to infer the evolution of the venom apparatus for this group. Our findings indicate that most of the genera of terebrids are polyphyletic, and one species (“Terebra” (s.l.) jungi) is the sister group to all other terebrids. Molecular analyses combined with mapping of venom apparatus morphology indicate that the Terebridae have lost the venom apparatus at least twice during their evolution. Species in the genera Terebra and Hastula have the typical venom apparatus found in most toxoglossate gastropods, but all other terebrid species do not. For venomous organisms, the dual analysis of molecular phylogeny and toxin function is an instructive combination for unraveling the larger questions of phylogeny and speciation. The results presented here suggest a paradigm shift in the current understanding of terebrid evolution, while presenting a road map for discovering novel terebrid toxins, a largely unexplored resource for biomedical research and potential therapeutic drug development.
Toxoglossa evolution; Terebridae phylogeny; venomous marine snails; peptide toxins; venom apparatus
The cone snails belong to the superfamily Conoidea, comprising ∼10,000 venomous marine gastropods. We determined the complete mitochondrial DNA sequence of Conus textile. The gene order is identical in Conus textile, Lophiotoma cerithiformis (another Conoidean gastropod), and the neogastropod Ilyanassa obsoleta, (not in the superfamily Conoidea). However, the intergenic interval between the coxI/coxII genes, was much longer in C. textile (165 bp) than in any other previously analyzed gastropod.
We used the intergenic region to evaluate evolutionary patterns. In most neogastropods and three conidean families the intergenic interval is small (<30 nucleotides). Within Conus, the variation is from 130-170 bp, and each different clade within Conus has a narrower size distribution. In Conasprella, a subgenus traditionally assigned to Conus, the intergenic regions vary between 200-500 bp, suggesting that the species in Conasprella are not congeneric with Conus. The intergenic region was used for phylogenetic analysis of a group of fish-hunting Conus, despite the short length resolution was better than using standard markers. Thus, the coxI/coxII intergenic region can be used both to define evolutionary relationships between species in a clade, and to understand broad evolutionary patterns across the large superfamily Conoidea.
Conus textile; coxI-coxII intergenic sequence; evolution; Superfamily Conoidea; Conasprella
Cone snail venoms have yielded pharmacologically-active natural products of exceptional scientific interest. However, cone snails are a small minority of venomous molluscan biodiversity, the vast majority being tiny venomous morphospecies in the family Turridae. A novel method called lumun-lumun opens access to these micromolluscs and their venoms. Old fishing nets are anchored to the sea bottom for a period of 1–6 months and marine biotas rich in small molluscs are established. In a single lumun-lumun community, we found a remarkable gastropod biodiversity (155 morphospecies). Venomous predators belonging to the superfamily Conoidea (36 morphospecies) were the largest group, the majority being micromolluscs in the family Turridae.
We carried out an initial analysis of the most abundant of the turrid morphospecies recovered, Clathurella (Lienardia) cincta (Dunker, 1871). In contrast to all cDNA clones characterized from cone snail venom ducts, one of the C. cincta clones identified encoded two different peptide precursors presumably translated from a single mRNA. The prospect of easily accessing so many different morphospecies of venomous marine snails raises intriguing toxinological possibilities: the 36 conoidean morphospecies in this one net alone have the potential to yield thousands of novel pharmacologically-active compounds.
Marine Biodiversity; turrids; venom peptides
Puillandre, N. et al. (2010) Genetic divergence and geographic variation in a deep-water cone lineage: molecular and morphological analyses of the Conus orbignyi complex (Mollusca: Conoidea).
The cone snails (family Conidae) are a hyperdiverse lineage of venomous gastropods. Two standard markers, COI and ITS2, were used to define six genetically-divergent groups within a subclade of Conidae that includes Conus orbignyi; each of these was then evaluated based on their shell morphology. We conclude that three forms, previously regarded as subspecies of Conus orbignyi are distinct species, now recognized as Conus orbignyi, Conus elokismenos and Conus coriolisi. In addition, three additional species (Conus pseudorbignyi, Conus joliveti and Conus comatosa) belong to this clade. Some of the proposed species (e.g., Conus elokismenos) are possibly in turn complexes comprising multiple species. Groups such as Conidae illustrate the challenges generally faced in species delimitation in biodiverse lineages. In the case of the Conus orbignyi complex, not only are there definable, genetically divergent lineages, but also considerable geographic variation within each group. Our study suggests that an intensive analysis of multiple specimens within a single locality helps to minimize the confounding effects of geographic variation and can be a useful starting point for circumscribing different species within such a confusing complex.
COI gene; Conidae; ITS2 gene; Phylogeny; Species delimitation
A novel peptide, pal9a, was purified from the venom duct extract of the turrid snail, Polystira albida (superfamily Conoidea, family Turridae), collected in the Gulf of Mexico. Its primary structure was determined by automated Edman degradation and confirmed by mass spectrometry. Turritoxin pal9a contains 34 amino acid residues, including 6 Cys residues arranged in the pattern C-C-C-C-C-C (framework IX, where “-“ represents one or more non-Cys amino acids), which characterizes the P-conotoxins. Peptide pal9a is the first P-conotoxin-like turritoxin characterized from a member of family Turridae of the Western Atlantic. The primary structure of turritoxin pal9a, NVCDGDACPDGVCRSGCTCDFNVAQRKDTCFYPQ-nh2 (-nh2, amidated C-terminus; calculated monoisotopic mass, 3679.48 Da; experimental monoisotopic mass, 3678.84 Da), shows variable degrees of low sequence similarity with framework IX-toxins from turrid (three species of Lophiotoma, and four species of Gemmula), terebrid (Hastula hectica), and Conus species of the Indo-Pacific (C. textile, C. gloriamaris, C. amadis, and C. litteratus) and of the Western Atlantic (C. regius). During the comparison of peptide pal9a with the other framework IX-toxins known to date, we realized that, in general, these peptides are hydrophilic, acidic compounds that have not been found in the fish-hunting Conus species studied thus far; we also found support for the notion that they may belong to several distinct gene superfamilies, even those from the same species. Given the broad distribution of framework IX-toxins within superfamily Conoidea, it will be interesting to identify the still-unknown molecular targets of P-conotoxins, P-conotoxin-like turritoxins, and P-conotoxin-like augertoxins.
Conoidea; Turridae; Polystira albida; turritoxin; P-conotoxin; framework IX
Venoms from cone snails (Conidae) have been extensively studied during the last decades, but those from other members of the suborder Toxoglossa, such as of Terebridae and Turridae superfamilies attracted less interest so far. Here, we report the effects of venom and gland extracts from three species of the superfamily Terebridae. By 2-electrode voltage-clamp technique the gland extracts were tested on Xenopus oocytes expressing nicotinic acetylcholine receptors (nAChRs) of rat neuronal (α3β2, α3β4, α4β2, α4β4, α7) and muscle subtypes (α1β1γδ), and expressing potassium (Kv1.2 and Kv1.3) and sodium channels (Nav1.2, 1.3, 1.4, 1.6). The extracts were shown to exhibit remarkably high inhibitory activities on almost all nAChRs tested, in particular on the α7 subtype suggesting the presence of peptides of the A-superfamily from the venom of Conus species. In contrast, no effects on the potassium and sodium channels tested were observed. The venoms of terebrid snails may offer an additional source of novel biologically active peptides.
Terebridae venom; gland extracts; acetylcholine receptors; potassium channels; sodium channels
Cone snails are venomous predatory marine neogastropods that belong to the species-rich superfamily of the Conoidea. So far, the mitochondrial genomes of two cone snail species (Conus textile and Conus borgesi) have been described, and these feed on snails and worms, respectively. Here, we report the mitochondrial genome sequence of the fish-hunting cone snail Conus consors and describe a novel putative control region (CR) which seems to be absent in the mitochondrial DNA (mtDNA) of other cone snail species. This possible CR spans about 700 base pairs (bp) and is located between the genes encoding the transfer RNA for phenylalanine (tRNA-Phe, trnF) and cytochrome c oxidase subunit III (cox3). The novel putative CR contains several sequence motifs that suggest a role in mitochondrial replication and transcription.
Described herein is a general approach to identify novel compounds using the biodiversity of a megadiverse group of animals; specifically, the phylogenetic lineage of the venomous gastropods that belong to the genus Conus (“cone snails”). Cone snail biodiversity was exploited to identify three new μ-conotoxins, BuIIIA, BuIIIB and BuIIIC, encoded by the fish-hunting species Conus bullatus. BuIIIA, BuIIIB and BuIIIC are strikingly divergent in their amino acid composition compared to previous μ-conotoxins known to target the voltage-gated Na channel skeletal muscle subtype Nav1.4. Our preliminary results indicate that BuIIIB and BuIIIC are potent inhibitors of Nav1.4 (average block ~96%, at a 1 μM concentration of peptide), displaying a very slow off-rate not seen in previously characterized μ-conotoxins that block Nav1.4. In addition, the three new Conus bullatus μ-conopeptides help to define a new branch of the M-superfamily of conotoxins, namely M-5. The exogene strategy used to discover these Na channel-inhibiting peptides was based on both understanding the phylogeny of Conus, as well as the molecular genetics of venom μ-conotoxin peptides previously shown to generally target voltage-gated Na channels. The discovery of BuIIIA, BuIIIB and BuIIIC Na channel blockers expands the diversity of ligands useful in determining the structure-activity relationship of voltage-gated sodium channels.
Biodiversity-derived compounds; Sodium channel ligands; exogenes
Neuropathic pain afflicts a large percentage of the global population. This form of chronic, intractable pain arises when the peripheral or central nervous systems are damaged, either directly by lesion or indirectly through disease. The comorbidity of neuropathic pain with other diseases, including diabetes, cancer, and AIDS, contributes to a complex pathogenesis and symptom profile. Because most patients present with neuropathic pain refractory to current first-line therapeutics, pharmaceuticals with greater efficacy in pain management are highly desired. In this review we discuss the growing application of ω-conotoxins, small peptides isolated from Conus species, in the management of neuropathic pain. These toxins are synthesized by predatory cone snails as a component of paralytic venoms. The potency and selectivity with which ω-conotoxins inhibit their molecular targets, voltage-gated Ca2+ channels, is advantageous in the treatment of neuropathic pain states, in which Ca2+ channel activity is characteristically aberrant. Although ω-conotoxins demonstrate analgesic efficacy in animal models of neuropathic pain and in human clinical trials, there remains a critical need to improve the convenience of peptide drug delivery methods, and reduce the number and severity of adverse effects associated with ω-conotoxin-based therapies.
neuropathic pain; voltage-gated calcium channel; omega-conotoxin; ziconotide
Cone snails, which are predatory marine gastropods, produce a cocktail of venoms used for predation, defense and competition. The major venom component, conotoxin, has received significant attention because it is useful in neuroscience research, drug development and molecular diversity studies. In this study, we report the genomic characterization of nine conotoxin gene superfamilies from 18 Conus species and investigate the relationships among conotoxin gene structure, molecular evolution and diversity. The I1, I2, M, O2, O3, P, S, and T superfamily precursors all contain three exons and two introns, while A superfamily members contain two exons and one intron. The introns are conserved within a certain gene superfamily, and also conserved across different Conus species, but divergent among different superfamilies. The intronic sequences contain many simple repeat sequences and regulatory elements that may influence conotoxin gene expression. Furthermore, due to the unique gene structure of conotoxins, the base substitution rates and the number of positively selected sites vary greatly among exons. Many more point mutations and trinucleotide indels were observed in the mature peptide exon than in the other exons. In addition, the first example of alternative splicing in conotoxin genes was found. These results suggest that the diversity of conotoxin genes has been shaped by point mutations and indels, as well as rare gene recombination or alternative splicing events, and that the unique gene structures could have made a contribution to the evolution of conotoxin genes.
The gem turrids (genus Gemmula Weinkauff, 1875) are venomous snails in the family Turridae. A gene superfamily of disulfide-rich peptides expressed in Gemmula venom ducts was characterized. Gemmula speciosa (Reeve, 1843), venom duct cDNA clones revealed two different conotoxin-like prepropeptide precursors, with identical signal sequences, a largely conserved pro region, and a cysteine-rich C-terminal mature peptide region. The conserved signal sequence was used to successfully amplify homologous genes from three other Gemmula species; all had the same pattern of Cys residues in the predicted mature venom peptide. Although the signal sequence and propeptide regions were highly conserved, the mature toxin regions diverged greatly in sequence, except that the Cys residues were conserved. We designate this as the Pg-gene superfamily (Pg-superfamily) of Gemmula venom peptides. Purification of two members of the family directly from G. speciosa venom was achieved; amino acid sequence analysis revealed that these peptides are highly posttranslationally modified. With at least 10-fold as many species of turrids as cone snails, identification of rapidly diversifying gene superfamilies such as the Pg-superfamily of Gemmula is essential before the facile and systematic discovery and characterization of peptide toxins from turrid venoms can be achieved.
Conoidea; Venom peptides; Exogene superfamilies; Turrids; Drug discovery
Cone snails produce a distinctive repertoire of venom peptides that are used both as a defense mechanism and also to facilitate the immobilization and digestion of prey. These peptides target a wide variety of voltage- and ligand-gated ion channels, which make them an invaluable resource for studying the properties of these ion channels in normal and diseased states, as well as being a collection of compounds of potential pharmacological use in their own right. Examples include the United States Food and Drug Administration (FDA) approved pharmaceutical drug, Ziconotide (Prialt®; Elan Pharmaceuticals, Inc.) that is the synthetic equivalent of the naturally occurring ω-conotoxin MVIIA, whilst several other conotoxins are currently being used as standard research tools and screened as potential therapeutic drugs in pre-clinical or clinical trials. These developments highlight the importance of driving conotoxin-related research. A PubMed query from 1 January 2007 to 31 August 2011 combined with hand-curation of the retrieved articles allowed for the collation of 98 recently identified conotoxins with therapeutic potential which are selectively discussed in this review. Protein sequence similarity analysis tentatively assigned uncharacterized conotoxins to predicted functional classes. Furthermore, conotoxin therapeutic potential for neurodegenerative disorders (NDD) was also inferred.
Conus; cone snail; peptide; neuropeptide; conotoxin; nicotinic acetylcholine receptor; sodium channel; calcium channel; potassium channel
Conus species are characterized by their hyperdiverse toxins, encoded by a few gene superfamilies. Our phylogenies of the genus, based on mitochondrial genes, confirm previous results that C. californicus is highly divergent from all other species. Genetic and biochemical analysis of their venom peptides comprise the fifteen most abundant conopeptides and over 50 mature cDNA transcripts from the venom duct. Although C. californicus venom retains many of the general properties of other Conus species, they share only half of the toxin gene superfamilies found in other Conus species. Thus, in these two lineages, approximately half of the rapidly diversifying gene superfamilies originated after an early Tertiary split. Such results demonstrate that, unlike endogenously acting gene families, these genes are likely to be significantly more restricted in their phylogenetic distribution. In concordance with the evolutionary duistance of C. californicus from other species, there are aspects of prey-capture behavior and prey preferences of this species that diverges significantly from all other Conus.
biodiversity; accelerated evolution; gene superfamilies; cone snail; exogenomics; phylogenetic relationships
The venomous marine gastropods, cone snails (genus Conus), inject prey with a lethal cocktail of conopeptides, small cysteine-rich peptides, each with a high affinity for its molecular target, generally an ion channel, receptor or transporter. Over the last decade, conopeptides have proven indispensable reagents for the study of vertebrate neurotransmission. Conus bullatus belongs to a clade of Conus species called Textilia, whose pharmacology is still poorly characterized. Thus the genomics analyses presented here provide the first step toward a better understanding the enigmatic Textilia clade.
We have carried out a sequencing survey of the Conus bullatus genome and venom-duct transcriptome. We find that conopeptides are highly expressed within the venom-duct, and describe an in silico pipeline for their discovery and characterization using RNA-seq data. We have also carried out low-coverage shotgun sequencing of the genome, and have used these data to determine its size, genome-wide base composition, simple repeat, and mobile element densities.
Our results provide the first global view of venom-duct transcription in any cone snail. A notable feature of Conus bullatus venoms is the breadth of A-superfamily peptides expressed in the venom duct, which are unprecedented in their structural diversity. We also find SNP rates within conopeptides are higher compared to the remainder of C. bullatus transcriptome, consistent with the hypothesis that conopeptides are under diversifying selection.
N-type Ca2+ channels (Cav2.2) play an important role in the transmission of pain signals to the central nervous system. ω-Conotoxin (CTx)-MVIIA, also called ziconotide (Prialt®), effectively alleviates pain, without causing addiction, by blocking the pores of these channels. Unfortunately, CTx-MVIIA has a narrow therapeutic window and produces serious side effects due to the poor reversibility of its binding to the channel. It would thus be desirable to identify new analgesic blockers with binding characteristics that lead to fewer adverse side effects.
Here we identify a new CTx, FVIA, from the Korean Conus Fulmen and describe its effects on pain responses and blood pressure. The inhibitory effect of CTx-FVIA on N-type Ca2+ channel currents was dose-dependent and similar to that of CTx-MVIIA. However, the two conopeptides exhibited markedly different degrees of reversibility after block. CTx-FVIA effectively and dose-dependently reduced nociceptive behavior in the formalin test and in neuropathic pain models, and reduced mechanical and thermal allodynia in the tail nerve injury rat model. CTx-FVIA (10 ng) also showed significant analgesic effects on writhing in mouse neurotransmitter- and cytokine-induced pain models, though it had no effect on acute thermal pain and interferon-γ induced pain. Interestingly, although both CTx-FVIA and CTx-MVIIA depressed arterial blood pressure immediately after administration, pressure recovered faster and to a greater degree after CTx-FVIA administration.
The analgesic potency of CTx-FVIA and its greater reversibility could represent advantages over CTx-MVIIA for the treatment of refractory pain and contribute to the design of an analgesic with high potency and low side effects.
Highly selective N-type voltage-gated calcium (CaV) channel inhibitors from cone snail venom (the ω-conotoxins) have emerged as a new class of therapeutics for the treatment of chronic and neuropathic pain. Earlier in 2005, Prialt (Elan) or synthetic ω-conotoxin MVIIA, was the first ω-conotoxin to be approved by Food and Drug Administration for human use. This review compares the action of three ω-conotoxins, GVIA, MVIIA and CVID, describing their structure-activity relationships and potential as leads for the design of improved N-type therapeutics that are more useful in the treatment of chronic pain.
ω-conotoxin; Structure-Activity relationship; pain
Most Kunitz proteins like BPTI and α-dendrotoxin are stabilized by three disulfide bonds. The crystal structure shows how subtle repacking of non-covalent interactions may compensate for disulfide bond loss in a naturally occurring two-disulfide variant, conkunitzin-S1, the first discovered member of a new conotoxin family.
Cone snails (Conus) are predatory marine mollusks that immobilize prey with venom containing 50–200 neurotoxic polypeptides. Most of these polypeptides are small disulfide-rich conotoxins that can be classified into families according to their respective ion-channel targets and patterns of cysteine–cysteine disulfides. Conkunitzin-S1, a potassium-channel pore-blocking toxin isolated from C. striatus venom, is a member of a newly defined conotoxin family with sequence homology to Kunitz-fold proteins such as α-dendrotoxin and bovine pancreatic trypsin inhibitor (BPTI). While conkunitzin-S1 and α-dendrotoxin are 42% identical in amino-acid sequence, conkunitzin-S1 has only four of the six cysteines normally found in Kunitz proteins. Here, the crystal structure of conkunitzin-S1 is reported. Conkunitzin-S1 adopts the canonical 310–β–β–α Kunitz fold complete with additional distinguishing structural features including two completely buried water molecules. The crystal structure, although completely consistent with previously reported NMR distance restraints, provides a greater degree of precision for atomic coordinates, especially for S atoms and buried solvent molecules. The region normally cross-linked by cysteines II and IV in other Kunitz proteins retains a network of hydrogen bonds and van der Waals interactions comparable to those found in α-dendrotoxin and BPTI. In conkunitzin-S1, glycine occupies the sequence position normally reserved for cysteine II and the special steric properties of glycine allow additional van der Waals contacts with the glutamine residue substituting for cysteine IV. Evolution has thus defrayed the cost of losing a disulfide bond by augmenting and optimizing weaker yet nonetheless effective non-covalent interactions.
conotoxin; BPTI; α-dendroxin; native chemical ligation; conus
The peptides in the venoms of predatory marine snails belonging to the genus Conus (‘cone snails’) have well-established therapeutic applications for the treatment of pain and epilepsy. This review discusses the neuroprotective and cardioprotective potential of four families of Conus peptides (conopeptides), including ω-conotoxins that target voltage-gated Ca2+ channels, conantokins that target NMDA receptors, μ-conotoxins that target voltage-gated Na+ channels, and κ- and κM-conotoxins that target K+ channels. The diversity of Conus peptides that have already been shown to exhibit neuroprotective/cardioprotective activity suggests that marine snail venoms are a potentially rich source of drug leads with diverse mechanisms.
conopeptide; conotoxin; neuroprotection; cardioprotection; analgesic
An impressive biodiversity (>10,000 species) of marine snails (suborder Toxoglossa or superfamily Conoidea) have complex venoms, containing ca. 100 biologically active, disulfide-rich peptides. In the genus Conus, the most intensively investigated toxoglossan lineage (~500 species), a small set of venom gene superfamilies undergo rapid sequence hyperdiversification within their mature toxin regions. Each major lineage of Toxoglossa has its own distinct set of venom gene superfamilies. Two recently identified venom gene superfamilies are expressed in the large Turridae clade, but not in Conus. Thus, as major venomous molluscan clades expand, a small set of lineage specific venom gene superfamilies undergo accelerated evolution. The juxtaposition of extremely conserved signal sequences with hypervariable mature peptide regions is unprecedented and raises the possibility that in these gene superfamilies, the signal sequences are conserved as a result of an essential role they play in enabling rapid sequence evolution of the region of the gene that encodes the active toxin.
venom peptides; accelerated evolution; Conidae; Turridae
Members of the predatory gastropod genus Conus use a venom comprised of a cocktail of peptide neurotoxins, termed conotoxins or conopeptides, to paralyze prey and conotoxin gene family members diversify via strong positive selection. Because Conus venoms are used primarily to subdue prey, the evolution of venoms is likely affected by predator-prey interactions.
To identify the selective forces that drive the differentiation of venoms within species of Conus, we examined the distribution of alleles of a polymorphic O-superfamily conotoxin locus of Conus ebraeus at Okinawa, Guam and Hawaii. Previous analyses of mitochondrial cytochrome oxidase I gene sequences suggest that populations of C. ebraeus, a worm-eating Conus, are not structured genetically in the western and central Pacific. Nonetheless, because the sample size from Guam was relatively low, we obtained additional data from this location and reexamined patterns of genetic variation at the mitochondrial gene at Okinawa, Guam and Hawaii. We also utilized a DNA-based approach to identify prey items of individuals of C. ebraeus from Guam and compared this information to published data on diets at Okinawa and Hawaii. Our results show that conotoxin allelic frequencies differ significantly among all three locations, with strongest differentiation at Hawaii. We also confirm previous inferences that C. ebraeus exhibits no genetic differentiation between Okinawa, Guam and Hawaii at the mitochondrial locus. Finally, DNA-based analyses show that eunicid polychaetes comprise the majority of the prey items of C. ebraeus at Guam; while this results compares well with observed diet of this species at Okinawa, C. ebraeus preys predominantly on nereid polychaetes at Hawaii.
These results imply that strong selection pressures affect conotoxin allelic frequencies. Based on the dietary information, the selection may derive from geographic variation in dietary specialization and local coevolutionary arms races between Conus and their prey.
The venom of cone snails (ssp. Conus), a genus of predatory mollusks, is a vast source of bioactive peptides. Conus venom expression is complex, and venom composition can vary considerably depending upon the method of extraction and the species of cone snail in question. The injected venom from Conus ermineus, the only fish-hunting cone snail species that inhabits the Atlantic Ocean, was characterized using nanoNMR spectroscopy, MALDI-TOF mass spectrometry, RP-HPLC and nanoLC–ESI-MS. These methods allowed us to evaluate the variability of the venom within this species. Single specimens of C. ermineus show unchanged injected venom mass spectra and HPLC profiles over time. However, there was significant variability of the injected venom composition from specimen to specimen, in spite of their common biogeographic origin. Using nanoLC–ESI-MS, we determined that over 800 unique conopeptides are expressed by this reduced set of C. ermineus specimens. This number is considerably larger than previous estimates of the molecular repertoire available to cone snails to immobilize prey. These results support the idea of the existence of a complex regulatory mechanism to express specific venom peptides for injection into prey. These intraspecies differences can be a result of a combination of genetic and environmental factors. The differential expression of venom components represents a neurochemical paradigm that warrants further investigation.
Cone snails; Conus ermineus; Injected venom; Intraspecies variability; Molecular fingerprint; NanoNMR; LC–ESI-MS; Conopeptides
Conus species of marine snails deliver a potent collection of toxins from the venom duct via a long proboscis attached to a harpoon tooth. Conotoxins are known to possess powerful neurological effects and some have been developed for therapeutic uses. Using mass-spectrometry based proteomics, qualitative and quantitative differences in conotoxin components were found in the proximal, central and distal sections of the C. textile venom duct suggesting specialization of duct sections for biosynthesis of particular conotoxins. Reversed phase HPLC followed by Orbitrap mass spectrometry and data analysis using SEQUEST and ProLuCID identified 31 conotoxin sequences and 25 post-translational modification (PTM) variants with King-Kong 2 peptide being the most abundant. Several previously unreported variants of known conopeptides and were found and this is the first time that HyVal is reported for a disulfide rich Conus peptide. Differential expression along the venom duct, production of PTM variants, alternative proteolytic cleavage sites, and venom processing enroute to the proboscis all appear to contribute to enriching the combinatorial pool of conopeptides and producing the appropriate formulation for a particular hunting situation. The complimentary tools of mass spectrometry-based proteomics and molecular biology can greatly accelerate the discovery of Conus peptides and provide insights on envenomation and other biological strategies of cone snails.
conotoxin; conopeptides; proteomics; differential expression; post-translational modification; Orbitrap
To date, studies conducted on cone snail venoms have attributed the origins of this complex mixture of neuroactive peptides entirely to gene expression by the secretory cells lining the lumen of the venom duct. However, specialized tissues such as the salivary glands also secrete their contents into the anterior gut and could potentially contribute some venom components injected into target animals; evidence supporting this possibility is reported here. Sequence analysis of a cDNA library created from a salivary gland of Conus pulicarius revealed the expression of two transcripts whose predicted gene products, after post-translational processing, strikingly resemble mature conopeptides belonging to the α-conotoxin family. These two transcripts, like α-conotoxin transcripts, putatively encode mature peptides containing the conserved A-superfamily cysteine pattern (CC-C-C) but, the highly conserved A-superfamily signal sequences were not present. Analysis of A-superfamily members expressed in the venom duct of the same C. pulicarius specimens revealed three putative α-conotoxin sequences; the salivary gland transcripts were not found in the venom duct cDNA library, suggesting that these α-conotoxins are salivary gland-specific. Therefore, expression of conotoxin-like gene products by the salivary gland could potentially add to the complexity of Conus venoms.
Conus pulicarius; α-conotoxins; cDNA libraries; salivary gland; alpha4/7; conopeptide; exogenomics