Putative gamma-conotoxins in vermivorous cone snails: the case of Conus delessertii

Proteomic analysis of the venom of Conus flavidus from Red Sea reveals potential pharmacological applications

BACKGROUND

Venomous marine cone snails produce unique neurotoxins called conopeptides or conotoxins, which are valuable for research and drug discovery. Characterizing Conus venom is important, especially for poorly studied species, as these tiny and steady molecules have considerable potential as research tools for detecting new pharmacological applications. In this study, a worm-hunting cone snail, Conus flavidus inhabiting the Red Sea coast were collected, dissected and the venom gland extraction was subjected to proteomic analysis to define the venom composition, and confirm the functional structure of conopeptides.

RESULTS

Analysis of C. flavidus venom identified 117 peptide fragments and assorted them to conotoxin precursors and non-conotoxin proteins. In this procedure, 65 conotoxin precursors were classified and identified to 16 conotoxin precursors and hormone superfamilies. In the venom of C. flavidus, the four conotoxin superfamilies T, A, O2, and M were the most abundant peptides, accounting for 75.8% of the total conotoxin diversity. Additionally, 19 non-conotoxin proteins were specified in the venom, as well as several potentially biologically active peptides with putative applications.

CONCLUSION

Our research displayed that the structure of the C. flavidus-derived proteome is similar to other Conus species and includes toxins, ionic channel inhibitors, insulin-like peptides, and hyaluronidase. This study provides a foundation for discovering new conopeptides from C. flavidus venom for pharmaceutical use.

Synthesis and evaluation of a novel analgesic conotoxin Lt7b that inhibits calcium currents and increases sodium currents

Conotoxins are promising neuropharmacological tools and drug candidates due to their high efficiency and specificity in targeting ion channels or neurotransmitter receptors. In this study, a novel O₂‐superfamily conotoxin, Lt7b, was synthesized and its pharmacological functions were evaluated. Lt7b with three modified amino acids and three disulfide bonds was successfully synthesized. CD spectra showed that Lt7b had a typical α‐helix in the secondary structure. Patch clamp experiments on rat DRG neurons showed that Lt7b could significantly inhibit calcium currents with an IC₅₀ value of 856 ± 95 nM. Meanwhile, 10 μM Lt7b could significantly increase the sodium currents by 77 ± 8%, but it had no obvious effects on the potassium currents in DRG neurons. In addition, patch clamp experiments on ion channel subtypes showed that 10 μM Lt7b could inhibit 7.0 ± 1.2%, 8.0 ± 1.5%, 4.6 ± 3.4%, and 9.5 ± 0.1% of the hCa_v1.2, hCa_v2.1, hCa_v2.2, and hCa_v3.2 currents, respectively, while it did not increase the rNa_v1.7, rNa_v1.8, hNa_v1.5, hNa_v1.7, and hNa_v1.8 currents. Lt7b had no obvious toxicity to HaCaT and ND7/23 cells up to 1 mM and significantly increased the pain threshold at the testing time of 0.5–4 h in a dose‐dependent manner in the mouse hotplate assay. This novel conotoxin Lt7b may be a useful tool for ion channel studies and analgesic drug development.

Proteomic analysis of Red Sea Conus taeniatus venom reveals potential biological applications

Background:

Diverse and unique bioactive neurotoxins known as conopeptides or conotoxins are produced by venomous marine cone snails. Currently, these small and stable molecules are of great importance as research tools and platforms for discovering new drugs and therapeutics. Therefore, the characterization of Conus venom is of great significance, especially for poorly studied species.

Methods:

In this study, we used bioanalytical techniques to determine the venom profile and emphasize the functional composition of conopeptides in Conus taeniatus, a neglected worm-hunting cone snail.

Results:

The proteomic analysis revealed that 84.0% of the venom proteins were between 500 and 4,000 Da, and 16.0% were > 4,000 Da. In C. taeniatus venom, 234 peptide fragments were identified and classified as conotoxin precursors or non-conotoxin proteins. In this process, 153 conotoxin precursors were identified and matched to 23 conotoxin precursors and hormone superfamilies. Notably, the four conotoxin superfamilies T (22.87%), O1 (17.65%), M (13.1%) and O2 (9.8%) were the most abundant peptides in C. taeniatus venom, accounting for 63.40% of the total conotoxin diversity. On the other hand, 48 non-conotoxin proteins were identified in the venom of C. taeniatus. Moreover, several possibly biologically active peptide matches were identified, and putative applications of the peptides were assigned.

Conclusion:

Our study showed that the composition of the C. taeniatus-derived proteome is comparable to that of other Conus species and contains an effective mix of toxins, ionic channel inhibitors and antimicrobials. Additionally, it provides a guidepost for identifying novel conopeptides from the venom of C. taeniatus and discovering conopeptides of potential pharmaceutical importance.

Marine Natural Products from the Yucatan Peninsula

Mexico is one of the three areas of the world with the greatest terrestrial and cultural biological diversity. The diversity of Mexican medicinal flora has been studied for a long time and several bioactive compounds have been isolated. The investigation of marine resources, and particularly the potential of Mexican marine resources, has not been intensively investigated, even though the Yucatan Peninsula occupies 17.4% of the total of the Mexican coast, with great biological diversity in its coasts and the ocean. There are very few studies on the chemistry of natural products from marine organisms that were collected along the coasts of the Yucatan Peninsula and most of them are limited to the evaluation of the biological activity of their organic extracts. The investigations carried out on marine species from the Yucatan Peninsula resulted in the identification of a wide structural variety of natural products that include polyketides, terpenoids, nitrogen compounds, and biopolymers with cytotoxic, antibacterial, antifouling, and neurotoxic activities. This review describes the literature of bioprospecting and the exploration of the natural product diversity of marine organisms from the coasts of the Yucatan Peninsula up to mid-2019.

Characterization of the venom of the vermivorous cone snail Conus fulgetrum

Over 200 components with molecular mass ranging mainly from 400 to 4000 Da were characterized from the venom of the vermivorous cone snail Conus fulgetrum that inhabit Egyptian Red Sea. One major component having a molecular mass of 2946 Da was purified by HPLC, and its primary structure was determined by a combination of Edman degradation and MS/MS analysis.

A New Member of Gamma-Conotoxin Family Isolated from Conus princeps Displays a Novel Molecular Target

A novel conotoxin, named as PiVIIA, was isolated from the venom of Conus princeps, a marine predatory cone snail collected in the Pacific Southern Coast of Mexico. Chymotryptic digest of the S-alkylated peptide in combination with liquid chromatography coupled to tandem mass spectrometry, were used to define the sequencing of this peptide. Eleven N-terminal amino acids were verified by automated Edman degradation. PiVIIA is a 25-mer peptide (CDAOTHYCTNYWγCCSGYCγHSHCW) with six cysteine residues forming three disulphide bonds, a hydroxyproline (O) and two gamma carboxyglutamic acid (γ) residues. Based on the arrangement of six Cys residues (C-C-CC-C-C), this conotoxin might belong to the O2-superfamily. Moreover, PiVIIA has a conserved motif (-γCCS-) that characterizes γ-conotoxins from molluscivorous Conus. Peptide PiVIIA has 45% sequence identity with γ-PnVIIA—the prototype of this family. Biological activity of PiVIIA was assessed by voltage-clamp recording in rat dorsal root ganglion neurons. Perfusion of PiVIIA in the µM range produces a significant increase in the Ca²⁺ currents, without significantly modifying the Na⁺, K⁺ or proton-gated acid sensing ionic currents. These results indicate that PiVIIA is a new conotoxin whose activity deserves further studies to define its potential use as a positive modulator of neuronal activity.

Unraveling the peptidome of the South African cone snails Conus pictus and Conus natalis

Venoms from cone snails (genus Conus) can be seen as an untapped cocktail of biologically active compounds, being increasingly recognized as an emerging source of peptide-based therapeutics. Cone snails are considered to be specialized predators that have evolved the most sophisticated peptide chemistry and neuropharmacology system for their own biological purposes by producing venoms which contains a structural and functional diversity of neurotoxins. These neurotoxins or conotoxins are often small cysteine-rich peptides which have shown to be highly selective ligands for a wide range of ion channels and receptors. Local habitat conditions have constituted barriers preventing the spreading of Conus species occurring along the coast of South Africa. Due to their scarceness, these species remain, therefore, extremely poorly studied. In this work, the venoms of two South African cone snails, Conus pictus, a vermivorous snail and Conus natalis, a molluscivorous snail, have been characterized in depth. In total, 26 novel peptides were identified. Comparing the venoms of both snails, interesting differences were observed regarding venom composition and molecular characteristics of these components.

Structural characterization of five post-translationally modified isomorphs of a novel putative delta-conotoxin from the vermivorous snail Conus delessertii from the Mexican Caribbean Sea

A novel peptide, de7b, was isolated from the venom of Conus delessertii, a worm-hunting species collected in the Caribbean Sea off the Yucatan Peninsula. Its primary structure was determined by automated Edman degradation and confirmed by mass spectrometry: it contains 28 amino acids, including six Cys residues. Peptide de7b is the second, O-conotoxin-like peptide isolated from the venom of this species, and it exists in different post-translationally modified isomorphs, some of which contain gamma-carboxy-glutamate (gamma) and/or 4-hydroxy-proline (O) at positions 4, 7, and/or 14. Its primary structure is DCI(P/O)GG(E/gamma)NCDVFR(O/P)YRCCSGYCILLLCA, with molecular masses varying from 3078.6 to 3154.6Da, depending on the number and kind of modified amino acid residues. Peptide de7b shows significant sequence identity with several O-conotoxins purified and biologically characterized from molluscivorous and piscivorous cone snails of the Indo-Pacific region, the tropical Atlantic and Eastern Pacific Oceans, especially with the delta-conotoxins but also with the omega-conotoxins from molluscivorous species, which suggests that it might affect voltage-gated Na(+) or Ca(2+)channels. Peptide de7b has 32% sequence identity with putative gamma-conotoxin de7a, previously characterized from the same species; both peptides contain the same number of amino acid residues and of non-Cys residues between the pairs of consecutive Cys residues. However, these peptides have charge differences at seven positions within the N-terminal half indicating that they might have distinct molecular targets that remain to be identified.

Vitamin K-dependent gamma-glutamylcarboxylation: an ancient posttranslational modification

The vitamin K-dependent carboxylase carries out the posttranslational modification of specific glutamate residues in proteins to gamma-carboxy glutamic acid (Gla) in the presence of reduced vitamin K, molecular oxygen, and carbon dioxide. In the process, reduced vitamin K is converted to vitamin K epoxide, which is subsequently reduced to vitamin K, by vitamin K epoxide reductase (VKOR) for use in the carboxylation reaction. The modification has a wide range of physiological implications, including hemostasis, bone calcification, and signal transduction. The enzyme interacts with a high affinity gamma-carboxylation recognition sequence (gamma-CRS) of the substrate and carries out multiple modifications of the substrate before the product is released. This mechanism ensures complete carboxylation of the Gla domain of the coagulation factors, which is essential for their biological activity. gamma-Carboxylation, originally discovered in mammals, is widely distributed in the animal kingdom. It has been characterized in sea squirt (Ciona intestinalis), in flies (Drosophila melanogaster), and in marine snails (Conus textile), none of which have a blood coagulation system similar to mammals. The cone snails express a large array of gamma-carboxylated peptides that modulate the activity of ion channels. These findings have led to the suggestion that gamma-carboxylation is an extracellular posttranslational modification that antedates the divergence of molluscs, arthropods, and chordates. I will first summarize recent understanding of gamma-carboxylase and gamma-carboxylation gleaned from experiments using the mammalian enzyme, and then I will briefly describe the available information on gamma-carboxylation in D. melanogaster and C. textile.

Marine natural products

This review covers the literature published in 2005 for marine natural products, with 704 citations (493 for the period January to December 2005) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (812 for 2005), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

An O-conotoxin from the vermivorous Conus spurius active on mice and mollusks

Here, we report the purification, amino acid sequence and a preliminary biological characterization of a peptide, sr7a, from the venom of Conus spurius, a vermivorous species collected in the Yucatan Channel, Mexico. The peptide consists of 32 amino acid residues (CLQFGSTCFLGDDDICCSGECFYSGGTFGICS&; &, amidated C-terminus) and contains six cysteines arranged in the pattern (C-C-CC-C-C) that characterizes the O-superfamily of conotoxins. This superfamily includes several pharmacological families (omega-, kappa-, muO-, delta- and gamma-conotoxins) that target Ca(2+), K(+), Na(+) and pacemaker voltage-gated ion channels. Compared with other O-conotoxins that were purified from venoms, this peptide displays sequence similarity with omega-SVIA (from Conus striatus), delta-TxVIA/B (from Conus textile), omega-CVID (from Conus catus) and kappa-PVIIA (from Conus purpurascens). At a dose of 250 pmol, peptide sr7a elicited hyperactivity when injected intracranially into mice and produced paralysis when injected into the pedal muscle of freshwater snails, Pomacea paludosa, but it had no apparent effect after intramuscular injection into the limpet Patella opea or the freshwater fish Lebistes reticulatus.

A Novel Conotoxin Inhibitor of Kv1.6 Channel and nAChR Subtypes Defines a New Superfamily of Conotoxins,

Using assay-directed fractionation of the venom from the vermivorous cone snail Conus planorbis, we isolated a new conotoxin, designated pl14a, with potent activity at both nicotinic acetylcholine receptors and a voltage-gated potassium channel subtype. pl14a contains 25 amino acid residues with an amidated C-terminus, an elongated N-terminal tail (six residues), and two disulfide bonds (1-3, 2-4 connectivity) in a novel framework distinct from other conotoxins. The peptide was chemically synthesized, and its three-dimensional structure was demonstrated to be well-defined, with an alpha-helix and two 3(10)-helices present. Analysis of a cDNA clone encoding the prepropeptide precursor of pl14a revealed a novel signal sequence, indicating that pl14a belongs to a new gene superfamily, the J-conotoxin superfamily. Five additional peptides in the J-superfamily were identified. Intracranial injection of pl14a in mice elicited excitatory symptoms that included shaking, rapid circling, barrel rolling, and seizures. Using the oocyte heterologous expression system, pl14a was shown to inhibit both a K+ channel subtype (Kv1.6, IC50 = 1.59 microM) and neuronal (IC50 = 8.7 microM for alpha3beta4) and neuromuscular (IC50 = 0.54 microM for alpha1beta1 epsilondelta) subtypes of the nicotinic acetylcholine receptor (nAChR). Similarities in sequence and structure are apparent between the middle loop of pl14a and the second loop of a number of alpha-conotoxins. This is the first conotoxin shown to affect the activity of both voltage-gated and ligand-gated ion channels.

Amino acid sequence and biological activity of a gamma-conotoxin-like peptide from the worm-hunting snail Conus austini

A novel 31-residue toxin, named as7a, was isolated and characterized from the venom of Conus austini, a vermivorous cone snail collected in the western Gulf of Mexico. The complete amino acid sequence, TCKQKGEGCSLDVgammaCCSSSCKPGGPLFDFDC, was determined by automatic Edman sequencing after reduction and alkylation. The sequence shows six Cys residues arranged in the pattern that defines the O-superfamily of conotoxins, and the sequence motif -gammaCCS-, which has only been found in the gamma-conotoxin family. The molecular mass of the native peptide was determined by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, which confirmed the chemical analyses and suggested a free C-terminus. The purified peptide elicited toxic effects in the freshwater snail Pomacea paludosa after intramuscular injection, but it had no effect when injected intracerebrally into mice. The structural similarity of peptide as7a to other gamma-conotoxins suggests that modulation of pacemaker channels could be responsible for its biological activity.