Solution conformation of alphaA-conotoxin EIVA, a potent neuromuscular nicotinic acetylcholine receptor antagonist from Conus ermineus

Cone snail species off the Brazilian coast and their venoms: a review and update

The genus Conus includes over 900 species of marine invertebrates known as cone snails, whose venoms are among the most powerful described so far. This potency is mainly due to the concerted action of hundreds of small bioactive peptides named conopeptides, which target different ion channels and membrane receptors and thus interfere with crucial physiological processes. By swiftly harpooning and injecting their prey and predators with such deadly cocktails, the slow-moving cone snails guarantee their survival in the harsh, competitive marine environment. Each cone snail species produces a unique venom, as the mature sequences of conopeptides from the venoms of different species share very little identity. This biochemical diversity, added to the numerous species and conopeptides contained in their venoms, results in an immense biotechnological and therapeutic potential, still largely unexplored. That is especially true regarding the bioprospection of the venoms of cone snail species found off the Brazilian coast - a region widely known for its biodiversity. Of the 31 species described in this region so far, only four - Conus cancellatus, Conus regius, Conus villepinii, and Conus ermineus - have had their venoms partially characterized, and, although many bioactive molecules have been identified, only a few have been actually isolated and studied. In addition to providing an overview on all the cone snail species found off the Brazilian coast to date, this review compiles the information on the structural and pharmacological features of conopeptides and other molecules identified in the venoms of the four aforementioned species, paving the way for future studies.

The 3/4- and 3/6-Subfamily Variants of α-Conotoxins GI and MI Exhibit Potent Inhibitory Activity against Muscular Nicotinic Acetylcholine Receptors

α-Conotoxins GI and MI belong to the 3/5 subfamily of α-conotoxins and potently inhibit muscular nicotinic acetylcholine receptors (nAChRs). To date, no 3/4- or 3/6-subfamily α-conotoxins have been reported to inhibit muscular nAChRs. In the present study, a series of new 3/4-, 3/6-, and 3/7-subfamily GI and MI variants were synthesized and functionally characterized by modifications of loop2. The results show that the 3/4-subfamily GI variant GI[∆8G]-II and the 3/6-subfamily variants GI[+13A], GI[+13R], and GI[+13K] displayed potent inhibition of muscular nAChRs expressed in Xenopus oocytes, with an IC₅₀ of 45.4–73.4 nM, similar to or slightly lower than that of wild-type GI (42.0 nM). The toxicity of these GI variants in mice appeared to be about a half to a quarter of that of wild-type GI. At the same time, the 3/7-subfamily GI variants showed significantly lower in vitro potency and toxicity. On the other hand, similar to the 3/6-subfamily GI variants, the 3/6-subfamily MI variants MI[+14R] and MI[+14K] were also active after the addition of a basic amino acid, Arg or Lys, in loop2, but the activity was not maintained for the 3/4-subfamily MI variant MI[∆9G]. Interestingly, the disulfide bond connectivity “C1–C4, C2–C3” in the 3/4-subfamily variant GI[∆8G]-II was significantly more potent than the “C1–C3, C2–C4” connectivity found in wild-type GI and MI, suggesting that disulfide bond connectivity is easily affected in the rigid 3/4-subfamily α-conotoxins and that the disulfide bonds significantly impact the variants’ function. This work is the first to demonstrate that 3/4- and 3/6-subfamily α-conotoxins potently inhibit muscular nAChRs, expanding our knowledge of α-conotoxins and providing new motifs for their further modifications.

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.

Snails In Silico: A Review of Computational Studies on the Conopeptides

Marine cone snails are carnivorous gastropods that use peptide toxins called conopeptides both as a defense mechanism and as a means to immobilize and kill their prey. These peptide toxins exhibit a large chemical diversity that enables exquisite specificity and potency for target receptor proteins. This diversity arises in terms of variations both in amino acid sequence and length, and in posttranslational modifications, particularly the formation of multiple disulfide linkages. Most of the functionally characterized conopeptides target ion channels of animal nervous systems, which has led to research on their therapeutic applications. Many facets of the underlying molecular mechanisms responsible for the specificity and virulence of conopeptides, however, remain poorly understood. In this review, we will explore the chemical diversity of conopeptides from a computational perspective. First, we discuss current approaches used for classifying conopeptides. Next, we review different computational strategies that have been applied to understanding and predicting their structure and function, from machine learning techniques for predictive classification to docking studies and molecular dynamics simulations for molecular-level understanding. We then review recent novel computational approaches for rapid high-throughput screening and chemical design of conopeptides for particular applications. We close with an assessment of the state of the field, emphasizing important questions for future lines of inquiry.

[Conotoxins: from the biodiversity of gastropods to new drugs]

A review describes general trends in research of conotoxins that are peptide toxins isolated from sea gastropods of the Conus genus, since the toxins were discovered in 1970th. There are disclosed a conotoxin classification, their structure diversity and different ways of action to their molecular targets, mainly, ion channels. In the applied aspect of conotoxin research, drug discovery and development is discussed, the drugs being based on conotoxin structure. A first exemplary drug is a ziconotide, which is an analgesic of new generation.

Molecular docking study on the α3β2 neuronal nicotinic acetylcholine receptor complexed with α-conotoxin GIC

Nicotinic acetylcholine receptors (nAChRs) are a diverse family of homo- or heteropentameric ligand-gated ion channels. Understanding the physiological role of each nAChR subtype and the key residues responsible for normal and pathological states is important. α-Conotoxin neuropeptides are highly selective probes capable of discriminating different subtypes of nAChRs. In this study, we performed homology modeling to generate the neuronal α3, β2 and β4 subunits using the x-ray structure of the α1 subunit as a template. The structures of the extracellular domains containing ligand binding sites in the α3β2 and α3β4 nAChR subtypes were constructed using MD simulations and ligand docking processes in their free and ligand-bound states using α-conotoxin GIC, which exhibited the highest α3β2 vs. α3β4 discrimination ratio. The results provide a reasonable structural basis for such a discriminatory ability, supporting the idea that the present strategy can be used for future investigations on nAChR-ligand complexes.

Cone snail milked venom dynamics--a quantitative study of Conus purpurascens

Milked venom from cone snails represent a novel biological resource with a proven track record for drug discovery. To strengthen this correlation, we undertook a chromatographic and mass spectrometric study of individual milked venoms from Conus purpurascens. Milked venoms demonstrate extensive peptide differentiation amongst individual specimens and during captivity. Individual snails were found to lack a consistent set of described conopeptides, but instead demonstrated the ability to change venom expression, composition and post-translational modification incorporation; all variations contribute to an increase in chemical diversity and prey targeting strategies. Quantitative amino acid analysis revealed that milked venom peptides are expressed at ranges up to 3.51-121.01 μM within single milked venom samples. This provides for a 6.37-20,965 fold-excess of toxin to induce apparent IC₅₀ for individual conopeptides identified in this study. Comparative molecular mass analysis of duct venom, milked venom and radula tooth extracts from single C. purpurascens specimens demonstrated a level of peptide continuity. Numerous highly abundant and unique conopeptides remain to be characterized. This study strengthens the notion that approaches in conopeptide drug lead discovery programs will potentially benefit from a greater understanding of the toxinological nature of the milked venoms of Conus.

A new subfamily of conotoxins belonging to the A-superfamily

Two novel conotoxins from vermivorous cone snails Conus pulicarius and Conus tessulatus, designated as Pu14.1 and ts14a, were identified by cDNA cloning and peptide purification, respectively. The signal sequence of Pu14.1 is identical to that of α-conotoxins, while its predicted mature peptide, pu14a, shares high sequence similarity with ts14a, with only one residue different in their first intercysteine loop, which contains 10 residues and is rich in proline. Both pu14a and ts14a contain four separate cysteines in framework 14 (C-C-C-C). Peptide pu14a was chemically synthesized, air oxidized, and the connectivity of its two disulfide bonds was determined to be C1-C3, C2-C4, which is the same as found in α-conotoxins. The synthetic pu14a induced a sleeping symptom in mice and was toxic to freshwater goldfish upon intramuscular injection. Using the Xenopus oocyte heterologous expression system, 1μM of pu14a demonstrated to inhibit the rat neuronal α3β2-containing as well as the mouse neuromuscular α1β1γδ subtypes of nicotinic acetylcholine receptors, and then rapidly dissociated from the receptors. However, this toxin had no inhibitory effect on potassium channels in mouse superior cervical ganglion neurons. According to the identical signal sequence to α-conotoxins, the unique cysteine framework and molecular target of pu14a, we propose that pu14a and ts14a may represent a novel subfamily in the A-superfamily, designated as α1-conotoxins.

NMR structure determination of alpha-conotoxin BuIA, a novel neuronal nicotinic acetylcholine receptor antagonist with an unusual 4/4 disulfide scaffold

We have determined a high-resolution three-dimensional structure of alpha-conotoxin BuIA, a 13-residue peptide toxin isolated from Conus bullatus. Despite its unusual 4/4 disulfide bond layout alpha-conotoxin BuIA exhibits strong antagonistic activity at alpha6/alpha3beta2beta3, alpha3beta2, and alpha3beta4 nAChR subtypes like some alpha4/7 conotoxins. alpha-Conotoxin BuIA lacks the C-terminal beta-turn present within the second disulfide loop of alpha4/7 conotoxins, having only a "pseudo omega-shaped" molecular topology. Nevertheless, it contains a functionally critical two-turn helix motif, a feature ubiquitously found in alpha4/7 conotoxins. Such an aspect seems mainly responsible for similarities in the receptor recognition profile of alpha-conotoxin BuIA to alpha4/7 conotoxins. Structural comparison of alpha-conotoxin BuIA with alpha4/7 conotoxins and alpha4/3 conotoxin ImI suggests that presence of the second helical turn portion of the two-turn helix motif in alpha4/7 and alpha4/4 conotoxins may be important for binding to the alpha3 and/or alpha6 subunit of nAChR.

Conotoxins down under

In the four decades since toxinologists in Australia and elsewhere started to investigate the active constituents of venomous cone snails, a wealth of information has emerged on the various classes of peptides and proteins that make their venoms such potent bioactive cocktails. This article provides an overview of the current state of knowledge of these venom constituents, several of which are of interest as potential human therapeutics as a consequence of their high potency and exquisite target specificity. With the promise of as many as 50,000 venom components across the entire Conus genus, many more interesting peptides can be anticipated.

Solution conformation of a neuronal nicotinic acetylcholine receptor antagonist α-conotoxin OmIA that discriminates α3 vs. α6 nAChR subtypes

alpha-Conotoxin OmIA from Conus omaria is the only alpha-conotoxin that shows a approximately 20-fold higher affinity to the alpha3beta2 over the alpha6beta2 subtype of nicotinic acetylcholine receptor. We have determined a three-dimensional structure of alpha-conotoxin OmIA by nuclear magnetic resonance spectroscopy. alpha-Conotoxin OmIA has an "omega-shaped" overall topology with His(5)-Asn(12) forming an alpha-helix. Structural features of alpha-conotoxin OmIA responsible for its selectivity are suggested by comparing its surface characteristics with other functionally related alpha4/7 subfamily conotoxins. Reduced size of the hydrophilic area in alpha-conotoxin OmIA seems to be associated with the reduced affinity towards the alpha6beta2 nAChR subtype.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) 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 (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.

Solution conformation of alpha-conotoxin GIC, a novel potent antagonist of alpha3beta2 nicotinic acetylcholine receptors

Alpha-conotoxin GIC is a 16-residue peptide isolated from the venom of the cone snail Conus geographus. Alpha-conotoxin GIC potently blocks the alpha3beta2 subtype of human nicotinic acetylcholine receptor, showing a high selectivity for neuronal versus muscle subtype [McIntosh, Dowell, Watkins, Garrett, Yoshikami, and Olivera (2002) J. Biol. Chem. 277, 33610-33615]. We have now determined the three-dimensional solution structure of alpha-conotoxin GIC by NMR spectroscopy. The structure of alpha-conotoxin GIC is well defined with backbone and heavy atom root mean square deviations (residues 2-16) of 0.53 A and 0.96 A respectively. Structure and surface comparison of alpha-conotoxin GIC with the other alpha4/7 subfamily conotoxins reveals unique structural aspects of alpha-conotoxin GIC. In particular, the structural comparison between alpha-conotoxins GIC and MII indicates molecular features that may confer their similar receptor specificity profile, as well as those that provide the unique binding characteristics of alpha-conotoxin GIC.