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.

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

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

Contryphan sequence diversity: Messy N-terminus processing, effects on chromatographic behaviour and mass spectrometric fragmentation.

Contryphans, peptides containing a single disulfide bond, are found abundantly in cone snail venom. The analysis of a large dataset of available contryphan sequences permits a classification based on the occurrence of proline residues at positions 2 and 5 within the macrocyclic 23-membered disulfide loop. Further sequence diversity is generated by variable proteolytic processing of the contryphan precursor proteins. In the majority of contryphans, presence of Pro at position 2 and a D-residue at position 3 leads to a slow conformational dynamics, manifesting as anomalous chromatographic profiles during LC analysis. LC-MS analysis of diverse contryphans suggests that elution profiles may be used as a rapid diagnostic for the presence of the Pro2-DXxx3 motif. Natural sequences from C.inscriptus and C.frigidus together with synthetic analogs permit the delineation of the features necessary for abnormal chromatographic behaviour. A diagnostic for the presence of Pro at position 5 is obtained by the observation of non-canonical fragment ions, generated by N-Cα bond cleavage at the dehydroalanine residue formed by disulfide cleavage. Anomalous LC profiles supports Pro at position 2, while non-canonical mass spectral fragments established Pro at position 5, providing a rapid method for contryphan analysis from LC-ESI-MS/MS profiles of crude Conus venom. SIGNIFICANCE: Contryphans are peptides, widely distributed in cone snail venom, which display extensive sequence diversity. Heterogeneity of proteolytic processing of contryphan precursor proteins, together with post-translational modifications contributes to contryphan diversity. Contryphans, identified by a combination of mass spectrometry and transcriptomic analysis, are classified on the basis of sequence features, primarily the number of proline residues within the disulfide loop. Conformational diversity arises in contryphans by cis-trans isomerization of Cys-Pro bonds, resulting in characteristic chromatographic profiles, permitting identification even in crude venom mixtures. Rapid identification of contryphans in cone snail peptide libraries is also facilitated by diagnostic mass spectral fragments arising by non-canonical cleavage of the N-Cα bond at Cys(7).

Significance of D- tryptophan in Contryphan-Ar1131 Conus peptide: Oxidative folding, trypsin binding, and photostabilization activity.

Distinct differences have been observed between L-tryptophan and D-tryptophan containing contryphan-Ar1131 in oxidative folding, trypsin binding, and photostabilization activity on avobenzone. [W5] contryphan-Ar1131 and [w5] contryphan-Ar1131 were chemically synthesized and characterized using RP-HPLC and mass spectrometry. Structural differences due to the change of configuration of tryptophan were evident from the optimized structures of contryphan-Ar1131 using density functional theory (DFT). The comparison of early events of oxidative folding has revealed the role of D-tryptophan in accelerating the formation of a disulfide bond. The optimized structures of the reduced form of peptides revealed the occurrence of aromatic-aromatic and aromatic-proline interactions in [w5] contryphan-Ar1131 which may be critical in aiding the oxidative folding reaction. The presence of the Lys6-Pro7 peptide bond indicates that contryphan-Ar1131 is resistant but may bind to trypsin allowing to assign the binding affinity of peptides to the protein surface. Competitive binding studies and molecular docking along with molecular dynamic (MD) simulations have revealed that [w5] contryphan-Ar1131 has more affinity for the active site of trypsin. Given tryptophan is a photostabilizer of FDA-approved chemical UV-A filter avobenzone, the report has compared the photostabilization activity of [W5]/ [w5] contryphan-Ar1131 on avobenzone under natural sunlight. [w5] contryphan-Ar1131 has better photostabilization activity than that of [W5] contryphan-Ar1131 and also individual D-tryptophan and L-tryptophan amino acids. These biochemical studies have highlighted the significance of D-tryptophan in contryphan-Ar1131 and its photostabilization activity on avobenzone may find applications in cosmetics.

Peptide antagonists of NMDA receptors: Structure-activity relationships for potential therapeutics.

The N-methyl-D-aspartate (NMDA) receptors are heteromeric cation channels involved in memory, learning, and synaptic plasticity. The dysfunction associated with NMDA receptors results in neurodegenerative conditions. The conantokins comprise a family of Conus venom peptides that induce sleep upon intracranial injection into young mice and are known to be NMDA receptor antagonists. This work comprehensibly documents the conantokins that have been characterized to date, focusing on the biochemistry, solution structures in the presence or absence of divalent cations, functions as selective NMDA receptor antagonists, and structure-activity relationships. Furthermore, the applications of conantokins as potential therapeutics for certain neurological conditions, including neuropathic pain, epilepsy, and ischaemia that are linked to NMDA receptor dysfunction are reviewed.

Venomics Reveals a Non-Compartmentalised Venom Gland in the Early Diverged Vermivorous Conus distans.

The defensive use of cone snail venom is hypothesised to have first arisen in ancestral worm-hunting snails and later repurposed in a compartmentalised venom duct to facilitate the dietary shift to molluscivory and piscivory. Consistent with its placement in a basal lineage, we demonstrate that the C. distans venom gland lacked distinct compartmentalisation. Transcriptomics revealed C. distans expressed a wide range of structural classes, with inhibitory cysteine knot (ICK)-containing peptides dominating. To better understand the evolution of the venom gland compartmentalisation, we compared C. distans to C. planorbis, the earliest diverging species from which a defence-evoked venom has been obtained, and fish-hunting C. geographus from the Gastridium subgenus that injects distinct defensive and predatory venoms. These comparisons support the hypothesis that venom gland compartmentalisation arose in worm-hunting species and enabled repurposing of venom peptides to facilitate the dietary shift from vermivory to molluscivory and piscivory in more recently diverged cone snail lineages.

Symmetric and asymmetric receptor conformation continuum induced by a new insulin.

Cone snail venoms contain a wide variety of bioactive peptides, including insulin-like molecules with distinct structural features, binding modes and biochemical properties. Here, we report an active humanized cone snail venom insulin with an elongated A chain and a truncated B chain, and use cryo-electron microscopy (cryo-EM) and protein engineering to elucidate its interactions with the human insulin receptor (IR) ectodomain. We reveal how an extended A chain can compensate for deletion of B-chain residues, which are essential for activity of human insulin but also compromise therapeutic utility by delaying dissolution from the site of subcutaneous injection. This finding suggests approaches to developing improved therapeutic insulins. Curiously, the receptor displays a continuum of conformations from the symmetric state to a highly asymmetric low-abundance structure that displays coordination of a single humanized venom insulin using elements from both of the previously characterized site 1 and site 2 interactions.

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.

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

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

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

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

Marine paralytic shellfish toxins: chemical properties, mode of action, newer analogues, and structure-toxicity relationship.

Up to the end of 2020Every year, the appearance of marine biotoxins causes enormous socio-economic damage worldwide. Among the major groups of biotoxins, paralytic shellfish toxins, comprising saxitoxin and its analogues (STXs), are the ones that cause the most severe effects on humans, including death. However, the knowledge that currently exists on their chemistry, properties and mode of toxicological action is disperse and partially outdated. This review intends to systematically compile the dispersed information, updating and complementing it. With this purpose, it addresses several aspects related to the molecular structure of these toxins. Special focus is given to the bioconversion reactions that may occur in the different organisms (dinoflagellates, bivalves, and humans) and the possible mediators involved. A critical review of the most recently discovered analogues, the M-series toxins, is presented. Finally, a deep discussion about the relationship between the molecular structure (e.g., effect of the substituting groups and the net charge of the molecules) and the toxic activity of these molecules is performed, proposing the concept of "toxicological traffic light" based on the toxicity equivalency factors (TEFs).

Identification of Glutamine Synthetase as a Contryphan-Bt Binding Protein by His-Tag Pull-Down.

BACKGROUND & OBJECTIVE: Contryphan-Bt is a D-tryptophan-containing disulfide-constrained decapeptide recently isolated from the venom of Conus betulinus. The molecular targets of contryphans are controversial, and the identification of its interacting proteins may be of great importance. METHODS: His-tag pull-down assays were performed to investigate intracellular binding proteins of contryphan-Bt from rat brain lysate. Bt-Acp-[His]6, a contryphan-Bt derivative containing hexahistidine tag, was synthesized and used as the bait. As a control, Acp-[His]6 was used to exclude nonspecific bindings. RESULTS: Glutamine synthetase was identified as a potential contryphan-Bt binding protein by pull-- down assays and subsequent LC-MS/MS. The binding of contryphan-Bt to glutamine synthetase was confirmed and determined using microscale thermophoresis, with a Kd of 74.02 ± 2.8 µM. The binding did not affect glutamine synthetase activity, suggesting that the interaction site was distinct from the catalytic center. CONCLUSION: Glutamine synthetase was identified as a novel contryphan-Bt binding protein. This is the first report in which the conopeptide binds to an intracellular protein.

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.

Synthesis, Structural and Pharmacological Characterizations of CIC, a Novel α-Conotoxin with an Extended N-Terminal Tail.

Cone snails are venomous marine predators that rely on fast-acting venom to subdue their prey and defend against aggressors. The conotoxins produced in the venom gland are small disulfide-rich peptides with high affinity and selectivity for their pharmacological targets. A dominant group comprises α-conotoxins, targeting nicotinic acetylcholine receptors. Here, we report on the synthesis, structure determination and biological activity of a novel α-conotoxin, CIC, found in the predatory venom of the piscivorous species Conus catus and its truncated mutant Δ-CIC. CIC is a 4/7 α-conotoxin with an unusual extended N-terminal tail. High-resolution NMR spectroscopy shows a major influence of the N-terminal tail on the apparent rigidity of the three-dimensional structure of CIC compared to the more flexible Δ-CIC. Surprisingly, this effect on the structure does not alter the biological activity, since both peptides selectively inhibit α3ß2 and α6/α3ß2ß3 nAChRs with almost identical sub- to low micromolar inhibition constants. Our results suggest that the N-terminal part of α-conotoxins can accommodate chemical modifications without affecting their pharmacology.

Post-translationally modified conopeptides: Biological activities and pharmacological applications.

Conus venoms comprise a large variety of biologically active peptides (conopeptides or conotoxins) that are employed for prey capture and other biological functions. Throughout the course of evolution of the cone snails, they have developed an envenomation scheme that necessitates a potent mixture of peptides, most of which are highly post-translationally modified, that can cause rapid paralysis of their prey. The great diversity of these peptides defines the ecological interactions and evolutionary strategy of cone snails. Such scheme has led to some pharmacological applications for pain, epilepsy, and myocardial infarction, that could be further explored to ultimately find unique peptide-based therapies. This review focuses on ∼ 60 representative post-translationally modified conopeptides that were isolated from Conus venoms. Various conopeptides reveal post-translational modifications of specific amino acids, such as hydroxylation of proline and lysine, gamma-carboxylation of glutamate, formation of N-terminal pyroglutamate, isomerization of l- to d-amino acid, bromination of tryptophan, O-glycosylation of threonine or serine, sulfation of tyrosine, and cysteinylation of cysteine, other than the more common disulfide crosslinking and C-terminal amidation. Many of the post-translationally modified peptides paved the way for the characterization, by alternative analytical methods, of other pharmacologically important peptides that are classified under 27 conopeptide families denoting pharmacological classes.

Conus venom fractions inhibit the adhesion of Plasmodium falciparum erythrocyte membrane protein 1 domains to the host vascular receptors.

Using high-throughput BioPlex assays, we determined that six fractions from the venom of Conus nux inhibit the adhesion of various recombinant PfEMP-1 protein domains (PF08_0106 CIDR1α3.1, PF11_0521 DBL2ß3, and PFL0030c DBL3X and DBL5e) to their corresponding receptors (CD36, ICAM-1, and CSA, respectively). The protein domain-receptor interactions permit P. falciparum-infected erythrocytes (IE) to evade elimination in the spleen by adhering to the microvasculature in various organs including the placenta. The sequences for the main components of the fractions, determined by tandem mass spectrometry, yielded four T-superfamily conotoxins, one (CC-Loop-CC) with I-IV, II-III connectivity and three (CC-Loop-CXaaC) with a I-III, II-IV connectivity. The 3D structure for one of the latter, NuxVA = GCCPAPLTCHCVIY, revealed a novel scaffold defined by double turns forming a hairpin-like structure stabilized by the two disulfide bonds. Two other main fraction components were a miniM conotoxin, and a O2-superfamily conotoxin with cysteine framework VI/VII. This study is the first one of its kind suggesting the use of conotoxins for developing pharmacological tools for anti-adhesion adjunct therapy against malaria. Similarly, mitigation of emerging diseases like AIDS and COVID-19, can also benefit from conotoxins as inhibitors of protein-protein interactions as treatment. BIOLOGICAL SIGNIFICANCE: Among the 850+ species of cone snail species there are hundreds of thousands of diverse venom exopeptides that have been selected throughout several million years of evolution to capture prey and deter predators. They do so by targeting several surface proteins present in target excitable cells. This immense biomolecular library of conopeptides can be explored for potential use as therapeutic leads against persistent and emerging diseases affecting non-excitable systems. We aim to expand the pharmacological reach of conotoxins/conopeptides by revealing their in vitro capacity to disrupt protein-protein and protein-polysaccharide interactions that directly contribute to pathology of Plasmodium falciparum malaria. This is significant for severe forms of malaria, which might be deadly even after treated with current parasite-killing drugs because of persistent cytoadhesion of P. falciparum infected erythrocytes even when parasites within red blood cells are dead. Anti-adhesion adjunct drugs would de-sequester or prevent additional sequestration of infected erythrocytes and may significantly improve survival of malaria patients. These results provide a lead for further investigations into conotoxins and other venom peptides as potential candidates for anti-adhesion or blockade-therapies. This study is the first of its kind and it suggests that conotoxins can be developed as pharmacological tools for anti-adhesion adjunct therapy against malaria. Similarly, mitigation of emerging diseases like AIDS and COVID-19, can also benefit from conotoxins as potential inhibitors of protein-protein interactions as treatment.

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.

Purification and Characterization of the Pink-Floyd Drillipeptide, a Bioactive Venom Peptide from Clavus davidgilmouri (Gastropoda: Conoidea: Drilliidae).

The cone snails (family Conidae) are the best known and most intensively studied venomous marine gastropods. However, of the total biodiversity of venomous marine mollusks (superfamily Conoidea, >20,000 species), cone snails comprise a minor fraction. The venoms of the family Drilliidae, a highly diversified family in Conoidea, have not previously been investigated. In this report, we provide the first biochemical characterization of a component in a Drilliidae venom and define a gene superfamily of venom peptides. A bioactive peptide, cdg14a, was purified from the venom of Clavus davidgilmouri Fedosov and Puillandre, 2020. The peptide is small (23 amino acids), disulfide-rich (4 cysteine residues) and belongs to the J-like drillipeptide gene superfamily. Other members of this superfamily share a conserved signal sequence and the same arrangement of cysteine residues in their predicted mature peptide sequences. The cdg14a peptide was chemically synthesized in its bioactive form. It elicited scratching and hyperactivity, followed by a paw-thumping phenotype in mice. Using the Constellation Pharmacology platform, the cdg14a drillipeptide was shown to cause increased excitability in a majority of non-peptidergic nociceptors, but did not affect other subclasses of dorsal root ganglion (DRG) neurons. This suggests that the cdg14a drillipeptide may be blocking a specific molecular isoform of potassium channels. The potency and selectivity of this biochemically characterized drillipeptide suggest that the venoms of the Drilliidae are a rich source of novel and selective ligands for ion channels and other important signaling molecules in the nervous system.

A turripeptide from Polystira nobilis venom inhibits human α3ß2 and α7 nicotinic acetylcholine receptors.

Almost all marine snails within superfamily Conoidea produce venoms containing numerous neuroactive peptides. Most toxins characterized from members of this superfamily are produced by species belonging to family Conidae. These toxins (conotoxins) affect diverse membrane proteins, such as voltage- and ligand-gated ion channels, including nicotinic acetylcholine receptors (nAChRs). Family Turridae has been considerably less studied than their Conidae counterpart and, therefore, turrid toxins (turritoxins) have just been barely described. Consequently, in this work the most prominent chromatographic (RP-HPLC) fractions from the East Pacific species Polystira nobilis venom duct extract were isolated. The biological activity of six selected fractions was assayed on human (h) α7 AChRs expressed in Xenopus laevis oocytes. One of these fractions, F21, inhibited the acetylcholine-elicited response by 62 ± 12%. Therefore, this fraction was further purified and the F21-2 peptide was obtained. This peptide (at 5.6 µM) strongly and irreversibly inhibited the acetylcholine-induced response on hα7 and hα3ß2 nAChRs, by 55 ± 4 and 91 ± 1%, respectively. Electrospray mass spectrometry indicates that the average molecular mass of this toxin is 12 358.80 Da. The affinity for hα3ß2 nAChRs is high (IC50 of 566.2 nM). A partial sequence without cysteines was obtained by automated Edman degradation: WFRSFKSYYGHHGSVYRPNEPNFRSFAS…; blastp search revealed that this sequence has low similarity to some non-Cys-containing turripeptides. This is the first report of a turritoxin from a species of the American Pacific and the second description of a turripeptide inhibiting nAChRs.

Critical residue properties for potency and selectivity of α-Conotoxin RgIA towards α9α10 nicotinic acetylcholine receptors.

The α9α10 nicotinic acetylcholine receptor (nAChR) has been characterized as an effective anti-pain target that functions through a non-opioid mechanism. However, as a pentameric ion channel comprised of two different subunits, the specific targeting of α9α10 nAChRs has proven challenging. Previously the 13-amino-acid peptide, RgIA, was shown to block α9α10 nAChRs with high potency and specificity. This peptide, characterized from the venom of the carnivorous marine snail, Conus regius, produced analgesia in several rodent models of chronic pain. Despite promising pre-clinical data in behavioral assays, the number of specific α9α10 nAChR antagonists remains small and the physiological mechanisms of analgesia remain cryptic. In this study, we implement amino-acid substitutions to definitively characterize the chemical properties of RgIA that contribute to its activity against α9α10 nAChRs. Using this mutational approach, we determined the vital role of biochemical side-chain properties and amino acids in the second loop that are amenable to substitutions to further engineer next-generation analogs for the blockade of α9α10 nAChRs.