Isolation and characterization of a T-superfamily conotoxin from Conus litteratus with targeting tetrodotoxin-sensitive sodium channels

Conotoxins Targeting Voltage-Gated Sodium Ion Channels

Voltage-gated sodium (NaV) channels are intimately involved in the generation and transmission of action potentials, and dysfunction of these channels may contribute to nervous system diseases, such as epilepsy, neuropathic pain, psychosis, autism, and cardiac arrhythmia. Many venom peptides selectively act on NaV channels. These include conotoxins, which are neurotoxins secreted by cone snails for prey capture or self-defense but which are also valuable pharmacological tools for the identification and/or treatment of human diseases. Typically, conotoxins contain two or three disulfide bonds, and these internal crossbraces contribute to conotoxins having compact, well defined structures and high stability. Of the conotoxins containing three disulfide bonds, some selectively target mammalian NaV channels and can block, stimulate, or modulate these channels. Such conotoxins have great potential to serve as pharmacological tools for studying the functions and characteristics of NaV channels or as drug leads for neurologic diseases related to NaV channels. Accordingly, discovering or designing conotoxins targeting NaV channels with high potency and selectivity is important. The amino acid sequences, disulfide bond connectivity, and three-dimensional structures are key factors that affect the biological activity of conotoxins, and targeted synthetic modifications of conotoxins can greatly improve their activity and selectivity. This review examines NaV channel-targeted conotoxins, focusing on their structures, activities, and designed modifications, with a view toward expanding their applications. SIGNIFICANCE STATEMENT: NaV channels are crucial in various neurologic diseases. Some conotoxins selectively target NaV channels, causing either blockade or activation, thus enabling their use as pharmacological tools for studying the channels' characteristics and functions. Conotoxins also have promising potential to be developed as drug leads. The disulfide bonds in these peptides are important for stabilizing their structures, thus leading to enhanced specificity and potency. Together, conotoxins targeting NaV channels have both immediate research value and promising future application prospects.

The T-1 conotoxin μ-SrVA from the worm hunting marine snail Conus spurius preferentially blocks the human NaV1.5 channel

Conotoxin sr5a had previously been identified in the vermivorous cone snail Conus spurius. This conotoxin is a highly hydrophobic peptide, with the sequence IINWCCLIFYQCC, which has a cysteine pattern "CC-CC" belonging to the T-1 superfamily. It is well known that this superfamily binds to molecular targets such as calcium channels, G protein-coupled receptors (GPCR), and neuronal nicotinic acetylcholine receptors (nAChR) and exerts an effect mainly in the central nervous system. However, its effects on other molecular targets are not yet defined, suggesting the potential of newly relevant molecular interactions. To find and demonstrate a potential molecular target for conotoxin sr5a electrophysiological assays were performed on three subtypes of voltage-activated sodium channels (Na_V1.5, Na_V1.6, and Na_V1.7) expressed in HEK-293 cells with three different concentrations of sr5a(200, 400, and 600 nM). 200 nM sr5a blocked currents mediated by Na_V1.5 by 33%, Na_V1.6 by 14%, and Na_V1.7 by 7%. The current-voltage (I-V) relationships revealed that conotoxin sr5a exhibits a preferential activity on the Na_V1.5 subtype; the activation of Na_V1.5 conductance was not modified by the blocking effect of sr5a, but sr5a affected the voltage-dependence of inactivation of channels. Since peptide sr5a showed a specific activity for a sodium channel subtype, we can assign a pharmacological family and rename it as conotoxin µ-SrVA.

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.

De novo transcriptome sequencing of triton shell Charonia lampas sauliae: Identification of genes related to neurotoxins and discovery of genetic markers

Charonia lampas sauliae (triton snails, triton shells or tritons; Mollusca, Caenogastropoda, Littorinimorpha, Ranellidae) is a marine species with a wide distribution. In Korea, this species is listed as vulnerable and is regionally protected as an endangered species. Here, we report the first comprehensive transcriptome dataset of C. lampas sauliae obtained using the Illumina HiSeq 2500 platform. In total, 97.68% of raw read sequences were processed as clean reads. Of the 577,478 contigs obtained, 146,026 sequences were predicted to contain coding regions. About 89.34% of all annotated unigene sequences showed homologous matches to protein sequences in PANM DB (Protostome database). Further, about one-third of the unigene sequences were annotated using the UniGene, Swiss-Prot, Clusters of Orthologous Groups (COG) and Gene Ontology (GO) databases. In total, 190 enzymes were predicted under key metabolic pathways under stood through Kyoto Encyclopedia of Genes and Genomes (KEGG) database annotation. Repetitive elements such as long terminal repeats (LTRs), short interspersed nuclear elements (SINEs), long interspersed nuclear elements (LINEs), and DNA elements were enriched in the unigene sequences. Among the identified transcripts were the channel proteins, some of which were blocked by tetrodotoxin, which is thought to be synthesized by symbiotic bacteria inhabiting the shells. In addition, conotoxin superfamily peptides, such as B-conotoxin, conotoxin superfamily T and alpha-conotoxin, were identified, which may have relevance to biomedical and evolutionary research. A transcriptome-wide search for polymorphic loci identified 21,568 simple sequence repeats (SSRs) in the unigene sequences. Most SSRs were dinucleotides, among which AC/GT was the dominant SSR type. The molecular and genetic resources revealed in this study could be utilized for investigations on the fitness of the species in the marine environment and sustainability in a changing habitat.

Discovery and characterization of the novel conotoxin Lv1d from Conus lividus that presents analgesic activity

Cone snails are predatory gastropod mollusks that are distributed in all tropical marine environments and contain small peptides (conotoxins) in their venom to capture prey. However, the biochemical and molecular aspects of conotoxins remain poorly understood. In this article, a novel α4/7-conotoxin, Lv1d, was obtained from the venom duct cDNA library of the worm-hunting Conus lividus collected from the South China Sea. The cDNA of Lv1c encodes a 65 residue conopeptide precursor, which consists of a 21 residue signal peptide, a 27 residue Pro region, and 17 residues of mature peptide. The mature peptide Lv1d was chemically synthesized according to the sequence GCCSDPPCRHKHQDLCG. It was found that 10 μM Lv1d can completely inhibit frog sciatic nerve-gastrocnemius muscle contractility within 60 min. Moreover, 100 μg/kg Lv1d showed good analgesic effects in mouse hot plate model and formalin test. Patch clamp experiments showed that 5 μM Lv1d can inhibit the cholinergic microexcitatory postsynaptic currents (mEPSCs) requency and amplitude of projection neurons in Drosophila. In conclusion, the synthesis of Lv1d and its biological and physiological data might contribute to the development of this peptide as a novel potential drug for therapeutic applications. This finding also expands the knowledge of the targeting mechanism of the α4/7-subfamily conotoxins.

Diversity of Conopeptides and Their Precursor Genes of Conus Litteratus

The venom of various Conus species is composed of a rich variety of unique bioactive peptides, commonly referred to as conotoxins (conopeptides). Most conopeptides have specific receptors or ion channels as physiologically relevant targets. In this paper, high-throughput transcriptome sequencing was performed to analyze putative conotoxin transcripts from the venom duct of a vermivorous cone snail species, Conus litteratus native to the South China Sea. A total of 128 putative conotoxins were identified, most of them belonging to 22 known superfamilies, with 43 conotoxins being regarded as belonging to new superfamilies. Notably, the M superfamily was the most abundant in conotoxins among the known superfamilies. A total of 15 known cysteine frameworks were also described. The largest proportion of cysteine frameworks were VI/VII (C-C-CC-C-C), IX (C-C-C-C-C-C) and XIV (C-C-C-C). In addition, five novel cysteine patterns were also discovered. Simple sequence repeat detection results showed that di-nucleotide was the major type of repetition, and the codon usage bias results indicated that the codon usage bias of the conotoxin genes was weak, but the M, O1, O2 superfamilies differed in codon preference. Gene cloning indicated that there was no intron in conotoxins of the B1- or J superfamily, one intron with 1273-1339 bp existed in a mature region of the F superfamily, which is different from the previously reported gene structure of conotoxins from other superfamilies. This study will enhance our understanding of conotoxin diversity, and the new conotoxins discovered in this paper will provide more potential candidates for the development of pharmacological probes and marine peptide drugs.

Neurobiological activity of conotoxins via sodium channel modulation

Conotoxins (CnTX) are bioactive peptides produced by marine molluscs belonging to Conus genus. The biochemical structure of these venomous peptides is characterized by a low number of amino acids linked with disulfide bonds formed by a high degree of post-translational modifications and glycosylation steps which increase the diversity and rate of evolution of these molecules. CnTX different isoforms are known to target ion channels and, in particular, voltage-gated sodium (Na⁺) channels (Na_v channels). These are transmembrane proteins fundamental in excitable cells for generating the depolarization of plasma membrane potential known as action potential which propagates electrical signals in muscles and nerves for physiological functions. Disorders in Na_v channel activity have been shown to induce neurological pathologies and pain states. Here, we describe the current knowledge of CnTX isoform modulation of the Na_v channel activity, the mechanism of action and the potential therapeutic use of these toxins in counteracting neurological dysfunctions.

Isolation and structural identification of a new T1-conotoxin with unique disulfide connectivities derived from Conus bandanus

Background:

Conopeptides are neuropharmacological peptides derived from the venomous salivary glands of cone snails. Among 29 superfamilies based on conserved signal sequences, T-superfamily conotoxins, which belong to the smallest group, include four different frameworks that contain four cysteines denominated I, V, X and XVI. In this work, the primary structure and the cysteine connectivity of novel conotoxin of Conus bandanus were determined by tandem mass spectrometry using collision-induced dissociation.

Methods:

The venom glands of C. bandanus snails were dissected, pooled, and extracted with 0.1% trifluoroacetic acid in three steps and lyophilized. The venom was fractionated and purified in an HPLC system with an analytical reversed-phase C₁₈ column. The primary peptide structure was analyzed by MALDI TOF MS/MS using collision-induced dissociation and confirmed by Edman's degradation. The peptide’s cysteine connectivity was determined by rapid partial reduction-alkylation technique.

Results:

The novel conotoxin, NGC₁C₂(I/L)VREC₃C₄, was firstly derived from de novo sequencing by MS/MS. The presence of isoleucine residues in this conotoxin was confirmed by the Edman degradation method. The conotoxin, denominated Bn5a, belongs to the T1-subfamily of conotoxins. However, the disulfide bonds (C₁-C₄/C₂-C₃) of Bn5a were not the same as found in other T1-subfamily conopeptides but shared common connectivities with T2-subfamily conotoxins. The T1-conotoxin of C. bandanus proved the complexity of the disulfide bond pattern of conopeptides. The homological analysis revealed that the novel conotoxin could serve as a valuable probe compound for the human-nervous-system norepinephrine transporter.

Conclusion:

We identified the first T1-conotoxin, denominated Bn5a, isolated from C. bandanus venom. However, Bn5a conotoxin exhibited unique C₁-C₄/C₂-C₃ disulfide connectivity, unlike other T1-conotoxins (C₁-C₃/C₂-C₄). The structural and homological analyses herein have evidenced novel conotoxin Bn5a that may require further investigation.

Structural and Functional Analyses of Cone Snail Toxins

Cone snails are marine gastropod mollusks with one of the most powerful venoms in nature. The toxins, named conotoxins, must act quickly on the cone snails´ prey due to the fact that snails are extremely slow, reducing their hunting capability. Therefore, the characteristics of conotoxins have become the object of investigation, and as a result medicines have been developed or are in the trialing process. Conotoxins interact with transmembrane proteins, showing specificity and potency. They target ion channels and ionotropic receptors with greater regularity, and when interaction occurs, there is immediate physiological decompensation. In this review we aimed to evaluate the structural features of conotoxins and the relationship with their target types.

Pharmacology of predatory and defensive venom peptides in cone snails

Cone snails are predatory gastropods whose neurotoxic venom peptides (conotoxins) have been extensively studied for pharmacological probes, venom evolution mechanisms and potential therapeutics. Conotoxins have a wide range of structural and functional classes that continue to undergo accelerated evolution that underlies the rapid expansion of the genus over their short evolutionary history. A number of pharmacological classes, driven by separately evolved defensive and predatory venoms, have been hypothesised to facilitate shifts in prey that exemplify the adaptability of cone snails. Here we provide an overview of these pharmacological families and discuss their ecological roles and evolutionary impact.

Total synthesis of μ-conotoxin lt5d

The total synthesis of μ-conotoxin lt5d is presented for the first time employing two different strategies.

The Venom Repertoire of Conus gloriamaris (Chemnitz, 1777), the Glory of the Sea

The marine cone snail Conus gloriamaris is an iconic species. For over two centuries, its shell was one of the most prized and valuable natural history objects in the world. Today, cone snails have attracted attention for their remarkable venom components. Many conotoxins are proving valuable as research tools, drug leads, and drugs. In this article, we present the venom gland transcriptome of C. gloriamaris, revealing this species' conotoxin repertoire. More than 100 conotoxin sequences were identified, representing a valuable resource for future drug discovery efforts.

A sleep-inducing peptide from the venom of the Indian cone snail Conus araneosus

The marine snail Conus araneosus has unusual significance due to its confined distribution to coastal regions of southeast India and Sri Lanka. Due to its relative scarceness, this species has been poorly studied. In this work, we characterized the venom of C. araneosus to identify new venom peptides. We identified 14 novel compounds. We determined amino acid sequences from chemically-modified and unmodified crude venom using liquid chromatography-electrospray ionization mass spectrometry and matrix assisted laser desorption ionization time-of-flight mass spectrometry. Ten sequences showed six Cys residues arranged in a pattern that is most commonly associated with the M-superfamily of conotoxins. Four other sequences had four Cys residues in a pattern that is most commonly associated with the T-superfamily of conotoxins. The post-translationally modified residue (pyroglutamate) was determined at the N-terminus of two sequences, ar3h and ar3i respectively. In addition, two sequences, ar3g and ar3h were C-terminally amidated. At a dose of 2 nmol, peptide ar3j elicited sleep when injected intraperitoneally into mice. To our knowledge, this is the first report of a peptide from a molluscivorous cone snail with sleep-inducing effects in mice. The novel peptides characterized herein extend the repertoire of unique peptides derived from cone snails and may add value to the therapeutic promise of conotoxins.

Conotoxin gene superfamilies

Conotoxins are the peptidic components of the venoms of marine cone snails (genus Conus). They are remarkably diverse in terms of structure and function. Unique potency and selectivity profiles for a range of neuronal targets have made several conotoxins valuable as research tools, drug leads and even therapeutics, and has resulted in a concerted and increasing drive to identify and characterise new conotoxins. Conotoxins are translated from mRNA as peptide precursors, and cDNA sequencing is now the primary method for identification of new conotoxin sequences. As a result, gene superfamily, a classification based on precursor signal peptide identity, has become the most convenient method of conotoxin classification. Here we review each of the described conotoxin gene superfamilies, with a focus on the structural and functional diversity present in each. This review is intended to serve as a practical guide to conotoxin superfamilies and to facilitate interpretation of the increasing number of conotoxin precursor sequences being identified by targeted-cDNA sequencing and more recently high-throughput transcriptome sequencing.

Novel M-Superfamily and T-Superfamily conotoxins and contryphans from the vermivorous snail Conus figulinus

The venom of Conus figulinus, a vermivorous cone snail, found in the south east coast of India, has been studied in an effort to identify novel peptide toxins. The amino acid sequences of seven peptides have been established using de novo mass spectrometric based sequencing methods. Among these, three peptides belong to the M-Superfamily conotoxins, namely, Fi3a, Fi3b, and Fi3c, and one that belongs to the T-Superfamily, namely, Fi5a. The other three peptides are contryphans, namely, contryphans fib, fic, and fid. Of these Fi3b, Fi3c, Fi5a, and contryphan fib are novel and are reported for the first time from venom of C. figulinus. The details of the sequencing methods and the relationship of these peptides with other 'M'-Superfamily conotoxins from the fish hunting and mollusk hunting clades are discussed. These novel peptides could serve as a lead compounds for the development of neuropharmacologically important drugs.

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

Observations of the mollusc-hunting cone snail Conus textile during feeding reveal that prey are often stung multiple times in succession. While studies on the venom peptides injected by fish-hunting cone snails have become common, these approaches have not been widely applied to the analysis of the injected venoms from mollusc-hunters. We have successfully obtained multiple injected venom samples from C. textile individuals, allowing us to investigate venom compositional variation during prey capture. Our studies indicate that C. textile individuals alter the composition of prey-injected venom peptides during single feeding events. The qualitative results obtained by MALDI-ToF mass spectrometry are mirrored by quantitative changes in venom composition observed by reverse-phase high performance liquid chromatography. While it is unclear why mollusc-hunting cone snails inject prey multiple times prior to engulfment, our study establishes for the first time a link between this behavior and compositional changes of the venom during prey capture. Changes in venom composition during hunting may represent a multi-step strategy utilized by these venomous animals to slow and incapacitate prey prior to engulfment.

Soluble expression, purification and functional identification of the framework XV conotoxins derived from different Conus species

The conotoxin cysteine framework XV (-C-C-CC-C-C-C-C-), which was named Lt15a, was firstly identified from the cDNA library of Conus litteratus. After that, 18 new framework XV conotoxin sequences were cloned from nine Conus species. Like other conopeptides, the XV-conotoxins have the conserved signal peptide and propeptide, and there are also some conserved residues in their mature peptide. All the framework XV conotoxins were apparently converged into two branches, because of the indel and point mutations occurred in their mature peptides. By fused with thioredoxin and 6×His tag, six XV-conotoxins were successfully expressed in Escherichia coli and purified. Different framework XV conotoxins have distinct biological activities on mice and frogs, and that may be related to the diversity of the toxin sequences. All the six XV-conotoxins had no obvious effects on the sodium currents of DRG neuron cells of Sprague-Dawley (SD) rats. The identification of this framework of conotoxins enriches our understanding of the structural and functional diversity of conotoxin.

Diversity of conotoxin gene superfamilies in the venomous snail, Conus victoriae

Animal venoms represent a vast library of bioactive peptides and proteins with proven potential, not only as research tools but also as drug leads and therapeutics. This is illustrated clearly by marine cone snails (genus Conus), whose venoms consist of mixtures of hundreds of peptides (conotoxins) with a diverse array of molecular targets, including voltage- and ligand-gated ion channels, G-protein coupled receptors and neurotransmitter transporters. Several conotoxins have found applications as research tools, with some being used or developed as therapeutics. The primary objective of this study was the large-scale discovery of conotoxin sequences from the venom gland of an Australian cone snail species, Conus victoriae. Using cDNA library normalization, high-throughput 454 sequencing, de novo transcriptome assembly and annotation with BLASTX and profile hidden Markov models, we discovered over 100 unique conotoxin sequences from 20 gene superfamilies, the highest diversity of conotoxins so far reported in a single study. Many of the sequences identified are new members of known conotoxin superfamilies, some help to redefine these superfamilies and others represent altogether new classes of conotoxins. In addition, we have demonstrated an efficient combination of methods to mine an animal venom gland and generate a library of sequences encoding bioactive peptides.

Identification, structural and pharmacological characterization of τ-CnVA, a conopeptide that selectively interacts with somatostatin sst3 receptor

Conopeptides are a diverse array of small linear and reticulated peptides that interact with high potency and selectivity with a large diversity of receptors and ion channels. They are used by cone snails for prey capture or defense. Recent advances in venom gland transcriptomic and venom peptidomic/proteomic technologies combined with bioactivity screening approaches lead to the identification of new toxins with original pharmacological profiles. Here, from transcriptomic/proteomic analyses of the Conus consors cone snail, we identified a new conopeptide called τ-CnVA, which displays the typical cysteine framework V of the T1-conotoxin superfamily. This peptide was chemically synthesized and its three-dimensional structure was solved by NMR analysis and compared to that of TxVA belonging to the same family, revealing very few common structural features apart a common orientation of the intercysteine loop. Because of the lack of a clear biological function associated with the T-conotoxin family, τ-CnVA was screened against more than fifty different ion channels and receptors, highlighting its capacity to interact selectively with the somatostatine sst3 receptor. Pharmacological and functional studies show that τ-CnVA displays a micromolar (Ki of 1.5μM) antagonist property for the sst3 receptor, being currently the only known toxin to interact with this GPCR subfamily.

Conotoxins targeting neuronal voltage-gated sodium channel subtypes: potential analgesics?

Voltage-gated sodium channels (VGSC) are the primary mediators of electrical signal amplification and propagation in excitable cells. VGSC subtypes are diverse, with different biophysical and pharmacological properties, and varied tissue distribution. Altered VGSC expression and/or increased VGSC activity in sensory neurons is characteristic of inflammatory and neuropathic pain states. Therefore, VGSC modulators could be used in prospective analgesic compounds. VGSCs have specific binding sites for four conotoxin families: μ-, μO-, δ- and ί-conotoxins. Various studies have identified that the binding site of these peptide toxins is restricted to well-defined areas or domains. To date, only the μ- and μO-family exhibit analgesic properties in animal pain models. This review will focus on conotoxins from the μ- and μO-families that act on neuronal VGSCs. Examples of how these conotoxins target various pharmacologically important neuronal ion channels, as well as potential problems with the development of drugs from conotoxins, will be discussed.

Conotoxins that confer therapeutic possibilities

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.

Identification, by RT-PCR, of four novel T-1-superfamily conotoxins from the vermivorous snail Conus spurius from the Gulf of Mexico

cDNA was prepared from the venom duct of a single Conus spurius specimen collected near the coast of Campeche, Mexico. From it, PCR products were generated, sequenced, and predicted to encode eight distinct precursors of T-1-conotoxins. These precursors contain five different mature toxins, of which four are novel and one (sr5a) has been previously purified and characterized from the venom of this species. Three of the novel toxins are very similar to sr5a: two have one amino acid substitution at position 8, whereas the other is predicted to have one additional residue at the C-terminus; the fourth toxin has five amino acid substitutions and is predicted to have two additional residues at the C-terminus. In general, the precursors include a 22-residue signal peptide, a 24-residue "pro" region, and a 13- to 16-residue mature toxin region; however, the C-termini of two mature toxin regions are predicted to be altered by post-translational processing. Three precursors lack, in the same positions, 15 amino acid residues included in the "pre" (one residue) and "pro" (14 residues) regions, which suggests the existence of an exon encoding the last signal peptide residue and the first 14 residues of the "pro" region. Phylogenetic analysis indicates that the T-1-conotoxin precursors and mature toxins of C. spurius are more similar to certain precursors and toxins from molluscivorous Conus species than to any precursors and toxins from vermivorous cones. The results reported here will be useful for synthesizing the novel toxins in order to identify their molecular targets.

Identification of a novel M-superfamily conotoxin with the ability to enhance tetrodotoxin sensitive sodium currents

In this work, a novel M-superfamily conotoxin, designated lt3a, was purified from the crude venom of Conus litteratus. Combined with peptide sequencing, MALDI-TOF mass spectrometry and cDNA cloning techniques, the amino acid sequence of lt3a was supposed to be DgammaCCgamma OQWCDGACDCCS, where O is hydroxyproline and gamma is carboxyglutamate. The Cys framework of lt3a (-CC-C-C-CC-) is similar to that of psi-, mu-, kappaM-conotoxins, which are representatives of M-conotoxins. Peptide lt3a is categorized into M1 branch based on the number of residues in the last Cys loop. Whole cell patch-clamp study on adult rat dorsal root ganglion neurons indicated that lt3a could enhance tetrodotoxin-sensitive sodium currents. This is a previously unknown function of M-superfamily conotoxins.

Marine natural products

This review covers the literature published in 2007 for marine natural products, with 948 citations(627 for the period January to December 2007) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, cnidarians,bryozoans, molluscs, tunicates, echinoderms and true mangrove plants. The emphasis is on new compounds (961 for 2007), together with the 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.1 Introduction, 2 Reviews, 3 Marine microorganisms and phytoplankton, 4 Green algae, 5 Brown algae, 6 Red algae, 7 Sponges, 8 Cnidarians, 9 Bryozoans, 10 Molluscs, 11 Tunicates (ascidians),12 Echinoderms, 13 Miscellaneous, 14 Conclusion, 15 References.

Identification and characterization of a novel O-superfamily conotoxin from Conus litteratus

A novel conotoxin named lt6c, an O-superfamily conotoxin, was identified from the cDNA library of venom duct of Conus litteratus. The full-length cDNA contains an open reading frame encoding a predicted 22-residue signal peptide, a 22-residue proregion and a mature peptide of 28 amino acids. The signal peptide sequence of lt6c is highly conserved in O-superfamily conotoxins and the mature peptide consists of six cysteines arranged in the pattern of C-C-CC-C-C that is defined the O-superfamily of conotoxins. The mature peptide fused with thioredoxin, 6-His tag, and a Factor Xa cleavage site was successfully expressed in Escherichia coli. About 12 mg lt6c was purified from 1L culture. Under whole-cell patch-clamp mode, lt6c inhibited sodium currents on adult rat dorsal root ganglion neurons. Therefore, lt6c is a novel O-superfamily conotoxin that is able to block sodium channels.