NMR Solution Structures of δ-Conotoxin EVIA from Conus ermineus That Selectively Acts on Vertebrate Neuronal Na+ Channels

δ-Conotoxin Structure Prediction and Analysis through Large-Scale Comparative and Deep Learning Modeling Approaches

The δ-conotoxins, a class of peptides produced in the venom of cone snails, are of interest due to their ability to inhibit the inactivation of voltage-gated sodium channels causing paralysis and other neurological responses, but difficulties in their isolation and synthesis have made structural characterization challenging. Taking advantage of recent breakthroughs in computational algorithms for structure prediction that have made modeling especially useful when experimental data is sparse, this work uses both the deep-learning-based algorithm AlphaFold and comparative modeling method RosettaCM to model and analyze 18 previously uncharacterized δ-conotoxins derived from piscivorous, vermivorous, and molluscivorous cone snails. The models provide useful insights into the structural aspects of these peptides and suggest features likely to be significant in influencing their binding and different pharmacological activities against their targets, with implications for drug development. Additionally, the described protocol provides a roadmap for the modeling of similar disulfide-rich peptides by these complementary methods.

Historical Perspective of the Characterization of Conotoxins Targeting Voltage-Gated Sodium Channels

Marine toxins have potent actions on diverse sodium ion channels regulated by transmembrane voltage (voltage-gated ion channels) or by neurotransmitters (nicotinic acetylcholine receptor channels). Studies of these toxins have focused on varied aspects of venom peptides ranging from evolutionary relationships of predator and prey, biological actions on excitable tissues, potential application as pharmacological intervention in disease therapy, and as part of multiple experimental approaches towards an understanding of the atomistic characterization of ion channel structure. This review examines the historical perspective of the study of conotoxin peptides active on sodium channels gated by transmembrane voltage, which has led to recent advances in ion channel research made possible with the exploitation of the diversity of these marine toxins.

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.

Conformational dynamics in peptide toxins: Implications for receptor interactions and molecular design

Peptide toxins are potent and often exquisitely selective probes of the structure and function of ion channels and receptors, and are therefore of significant interest to the pharmaceutical and biotech industries as both pharmacological tools and therapeutic leads. The three-dimensional structures of peptide toxins are essential as a basis for understanding their structure-activity relationships and their binding to target receptors, as well as in guiding the design of analogues with modified potency and/or selectivity for key targets. NMR spectroscopy has played a key role in elucidating the structures of peptide toxins and probing their structure-function relationships. In this article, we highlight the additional important contribution of NMR to characterising the dynamics of peptide toxins. We also compare the information available from NMR measurements with that afforded by molecular dynamics simulations. We describe several examples of the importance of dynamics measurements over a range of timescales for understanding the structure-function relationships of peptide toxins and their receptor engagement. Peptide toxins that inhibit the voltage-gated potassium channel K_V1.3 with pM affinities display different degrees of conformational flexibility, even though they contain multiple disulfide bonds, and this flexibility can affect the relative orientation of residues that have been shown to be critical for channel binding. Information on the dynamic properties of peptide toxins is important in the design of analogues or mimetics where receptor-bound structures are not available.

Predicted structural mimicry of spike receptor-binding motifs from highly pathogenic human coronaviruses

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Potential coronavirus spike protein mimicry revealed by structural comparison.

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Human and non-human protein potential interactions with virus identified.

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Predicted structural mimicry corroborated by protein–protein docking.

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Epitope-based alignments may help guide vaccine efforts.

Viruses often encode proteins that mimic host proteins in order to facilitate infection. Little work has been done to understand the potential mimicry of the SARS-CoV-2, SARS-CoV, and MERS-CoV spike proteins, particularly the receptor-binding motifs, which could be important in determining tropism and druggability of the virus. Peptide and epitope motifs have been detected on coronavirus spike proteins using sequence homology approaches; however, comparing the three-dimensional shape of the protein has been shown as more informative in predicting mimicry than sequence-based comparisons. Here, we use structural bioinformatics software to characterize potential mimicry of the three coronavirus spike protein receptor-binding motifs. We utilize sequence-independent alignment tools to compare structurally known protein models with the receptor-binding motifs and verify potential mimicked interactions with protein docking simulations. Both human and non-human proteins were returned for all three receptor-binding motifs. For example, all three were similar to several proteins containing EGF-like domains: some of which are endogenous to humans, such as thrombomodulin, and others exogenous, such as Plasmodium falciparum MSP-1. Similarity to human proteins may reveal which pathways the spike protein is co-opting, while analogous non-human proteins may indicate shared host interaction partners and overlapping antibody cross-reactivity. These findings can help guide experimental efforts to further understand potential interactions between human and coronavirus proteins.

Human health and snails

Snails can provide a considerable variety of bioactive compounds for cosmetic and pharmaceutical industries, useful for the development of new formulations with less toxicity and post effects compared to regular compounds used for the purpose. Compounds from crude extract, mucus, slime consist of glycans, polypeptides, proteins, etc., and can be used for curing diseases like viral lesions, warts, and different dermal problems. Some particular uses of snails involve treating post-traumatic stress. Micro RNA of Lymnaea stagnalis, was known to be responsible for the development of long-term memory and treatment of Alzheimer's and Dementia like diseases. This review explores the application of various bioactive compounds from snails with its potential as new translational medicinal and cosmetic applications. Snail bioactive compounds like ω-MVIIA, μ-SIIIA, μO-MrVIB, Xen2174, δ-EVIA, α-Vc1.1, σ-GVIIA, Conantokin-G, and Contulakin-G, conopeptides can be used for the development of anti-cancer drugs. These compounds target the innate immunity and improve the defense system of humans and provide protection against these life-threatening health concerns.AbbreviationsFDA: Food and Drug Administration; UTI: urinal tract infection; nAChRs: nicotinic acetylcholine receptors; NMDA: N-methyl-D-aspartate; CNS: central nervous system; CAR T: chimeric antigen receptors therapy; Micro RNA: micro ribonucleic acid.

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.

Conotoxin Diversity in Chelyconus ermineus (Born, 1778) and the Convergent Origin of Piscivory in the Atlantic and Indo-Pacific Cones

The transcriptome of the venom duct of the Atlantic piscivorous cone species Chelyconus ermineus (Born, 1778) was determined. The venom repertoire of this species includes at least 378 conotoxin precursors, which could be ascribed to 33 known and 22 new (unassigned) protein superfamilies, respectively. Most abundant superfamilies were T, W, O1, M, O2, and Z, accounting for 57% of all detected diversity. A total of three individuals were sequenced showing considerable intraspecific variation: each individual had many exclusive conotoxin precursors, and only 20% of all inferred mature peptides were common to all individuals. Three different regions (distal, medium, and proximal with respect to the venom bulb) of the venom duct were analyzed independently. Diversity (in terms of number of distinct members) of conotoxin precursor superfamilies increased toward the distal region whereas transcripts detected toward the proximal region showed higher expression levels. Only the superfamilies A and I3 showed statistically significant differential expression across regions of the venom duct. Sequences belonging to the alpha (motor cabal) and kappa (lightning-strike cabal) subfamilies of the superfamily A were mainly detected in the proximal region of the venom duct. The mature peptides of the alpha subfamily had the α4/4 cysteine spacing pattern, which has been shown to selectively target muscle nicotinic-acetylcholine receptors, ultimately producing paralysis. This function is performed by mature peptides having a α3/5 cysteine spacing pattern in piscivorous cone species from the Indo-Pacific region, thereby supporting a convergent evolution of piscivory in cones.

Sodium channels and pain: from toxins to therapies

Voltage-gated sodium channels (NaV channels) are essential for the initiation and propagation of action potentials that critically influence our ability to respond to a diverse range of stimuli. Physiological and pharmacological studies have linked abnormal function of NaV channels to many human disorders, including chronic neuropathic pain. These findings, along with the description of the functional properties and expression pattern of NaV channel subtypes, are helping to uncover subtype specific roles in acute and chronic pain and revealing potential opportunities to target these with selective inhibitors. High-throughput screens and automated electrophysiology platforms have identified natural toxins as a promising group of molecules for the development of target-specific analgesics. In this review, the role of toxins in defining the contribution of NaV channels in acute and chronic pain states and their potential to be used as analgesic therapies are discussed.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

The pharmacology of voltage-gated sodium channel activators

Toxins and venom components that target voltage-gated sodium (Na_V) channels have evolved numerous times due to the importance of this class of ion channels in the normal physiological function of peripheral and central neurons as well as cardiac and skeletal muscle. Na_V channel activators in particular have been isolated from the venom of spiders, wasps, snakes, scorpions, cone snails and sea anemone and are also produced by plants, bacteria and algae. These compounds have provided key insight into the molecular structure, function and pathophysiological roles of Na_V channels and are important tools due to their at times exquisite subtype-selectivity. We review the pharmacology of Na_V channel activators with particular emphasis on mammalian isoforms and discuss putative applications for these compounds. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

δ-Conotoxins synthesized using an acid-cleavable solubility tag approach reveal key structural determinants for NaV subtype selectivity

Conotoxins are venom peptides from cone snails with multiple disulfide bridges that provide a rigid structural scaffold. Typically acting on ion channels implicated in neurotransmission, conotoxins are of interest both as tools for pharmacological studies and as potential new medicines. δ-Conotoxins act by inhibiting inactivation of voltage-gated sodium channels (Nav). Their pharmacology has not been extensively studied because their highly hydrophobic character makes them difficult targets for chemical synthesis. Here we adopted an acid-cleavable solubility tag strategy that facilitated synthesis, purification, and directed disulfide bridge formation. Using this approach we readily produced three native δ-conotoxins from Conus consors plus two rationally designed hybrid peptides. We observed striking differences in Nav subtype selectivity across this group of compounds, which differ in primary structure at only three positions: 12, 23, and 25. Our results provide new insights into the structure-activity relationships underlying the Nav subtype selectivity of δ-conotoxins. Use of the acid-cleavable solubility tag strategy should facilitate synthesis of other hydrophobic peptides with complex disulfide bridge patterns.

Solution structure and in silico binding of a cyclic peptide with hepatitis B surface antigen

A specific ligand targeting the immunodominant region of hepatitis B virus is desired in neutralizing the infectivity of the virus. In a previous study, a disulfide constrained cyclic peptide cyclo S(1) ,S(9) Cys-Glu-Thr-Gly-Ala-Lys-Pro-His-Cys (S(1) , S(9) -cyclo-CETGAKPHC) was isolated from a phage displayed cyclic peptide library using an affinity selection method against hepatitis B surface antigen. The cyclic peptide binds tightly to hepatitis B surface antigen with a relative dissociation constant (KD (rel) ) of 2.9 nm. The binding site of the peptide was located at the immunodominant region on hepatitis B surface antigen. Consequently, this study was aimed to elucidate the structure of the cyclic peptide and its interaction with hepatitis B surface antigen in silico. The solution structure of this cyclic peptide was solved using (1) H, (13) C, and (15) N NMR spectroscopy and molecular dynamics simulations with NMR-derived distance and torsion angle restraints. The cyclic peptide adopted two distinct conformations due to the isomerization of the Pro residue with one structured region in the ETGA sequence. Docking studies of the peptide ensemble with a model structure of hepatitis B surface antigen revealed that the cyclic peptide can potentially be developed as a therapeutic drug that inhibits the virus-host interactions.

The Arabidopsis peptide kiss of death is an inducer of programmed cell death

Programmed cell death (PCD) has a key role in defence and development of all multicellular organisms. In plants, there is a large gap in our knowledge of the molecular machinery involved at the various stages of PCD, especially the early steps. Here, we identify kiss of death (KOD) encoding a 25-amino-acid peptide that activates a PCD pathway in Arabidopsis thaliana. Two mutant alleles of KOD exhibited a reduced PCD of the suspensor, a single file of cells that support embryo development, and a reduced PCD of root hairs after a 55°C heat shock. KOD expression was found to be inducible by biotic and abiotic stresses. Furthermore, KOD expression was sufficient to cause death in leaves or seedlings and to activate caspase-like activities. In addition, KOD-induced PCD required light in leaves and was repressed by the PCD-suppressor genes AtBax inhibitor 1 and p35. KOD expression resulted in depolarization of the mitochondrial membrane, placing KOD above mitochondria dysfunction, an early step in plant PCD. A KOD∷GFP fusion, however, localized in the cytosol of cells and not mitochondria.

Development of a functional cis-prolyl bond biomimetic and mechanistic implications for nickel superoxide dismutase

During recent years several peptide-based Ni superoxide dismutase (NiSOD) models have been developed. These NiSOD models show an important structural difference compared to the native NiSOD enzyme, which could cause a completely different mechanism of superoxide dismutation. In the native enzyme the peptide bond between Leu4 and Pro5 is cis-configured, while the NiSOD models exhibit a trans-configured peptide bond between these two residues. To shed light on how the configuration of this single peptide bond influences the activity of the NiSOD model peptides, a new cis-prolyl bond surrogate was developed. As surrogate we chose a leucine/alanine-based disubstituted 1,2,3-triazole, which was incorporated into the NiSOD model peptide replacing residues Leu4 and Pro5. The yielded 1,5-disubstituted triazole nickel peptide exhibited high SOD activity, which was approximately the same activity as its parent trans-configured analogue. Hence, the conformation of the prolyl peptide bond apparently has of minor importance for the catalytic activity of the metallopeptides as postulated in literature. Furthermore, it is shown that the triazole metallopeptide is forming a stable cyanide adduct as a substrate analogue model complex.

Conotoxins: molecular and therapeutic targets

Marine molluscs known as cone snails produce beautiful shells and a complex array of over 50,000 venom peptides evolved for prey capture and defence. Many of these peptides selectively modulate ion channels and transporters, making them a valuable source of new ligands for studying the role these targets play in normal and disease physiology. A number of conopeptides reduce pain in animal models, and several are now in pre-clinical and clinical development for the treatment of severe pain often associated with diseases such as cancer. Less than 1% of cone snail venom peptides are pharmacologically characterised.

Conus ventricosus venom peptides profiling by HPLC-MS: a new insight in the intraspecific variation

Conus is a genus of predatory marine gastropods that poison the prey with a complex mixture of compounds active on muscle and nerve cells. An individual cone snail's venom contains a mixture of pharmacological agents, mostly short, structurally constrained peptides. This study is focused on the composition of the venom employed by Conus ventricosus Gmelin, 1791, a worm-hunting cone snail living in the Mediterranean Sea. For this purpose, LC coupled to MS techniques has been successfully used to establish qualitative and quantitative differences in conopeptides from minute amounts of venom ducts. We were able to prove variability in the venom conopeptide complement, possibly related to different trophic habits of the species in the Mediterranean Sea. Moreover, the information-rich MS techniques enabled us to identify two novel C. ventricosus peptides, here named Conotoxin-Vn and -Conotoxin-Vn. On the basis of the structural data collected so far, we suggest that Conotoxin-Vn is a conopeptide belonging to the -family that recognizes calcium channels through a specific pharmacophore. Similarly, molecular modeling data suggest that -Conotoxin-Vn should represent a competitive antagonist of neuronal nicotinic acetylcholine receptors (nAChRs).

Solution structure of delta-Am2766: a highly hydrophobic delta-conotoxin from Conus amadis that inhibits inactivation of neuronal voltage-gated sodium channels

The three-dimensional (3D) NMR solution structure (MeOH) of the highly hydrophobic delta-conotoxin delta-Am2766 from the molluscivorous snail Conus amadis has been determined. Fifteen converged structures were obtained on the basis of 262 distance constraints, 25 torsion-angle constraints, and ten constraints based on disulfide linkages and H-bonds. The root-mean-square deviations (rmsd) about the averaged coordinates of the backbone (N, C(alpha), C) and (all) heavy atoms were 0.62+/-0.20 and 1.12+/-0.23 A, respectively. The structures determined are of good stereochemical quality, as evidenced by the high percentage (100%) of backbone dihedral angles that occupy favorable and additionally allowed regions of the Ramachandran map. The structure of delta-Am2766 consists of a triple-stranded antiparallel beta-sheet, and of four turns. The three disulfides form the classical 'inhibitory cysteine knot' motif. So far, only one tertiary structure of a delta-conotoxin has been reported; thus, the tertiary structure of delta-Am2766 is the second such example. Another Conus peptide, Am2735 from C. amadis, has also been purified and sequenced. Am2735 shares 96% sequence identity with delta-Am2766. Unlike delta-Am2766, Am2735 does not inhibit the fast inactivation of Na+ currents in rat brain Na(v)1.2 Na+ channels at concentrations up to 200 nM.

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.

Effects of δ-Conotoxins PVIA and SVIE on Sodium Channels in the Amphibian Sympathetic Nervous System

δ-Conotoxins are a family of small, disulfide-rich peptides found in the venoms of predatory cone snails ( Conus). We examined in detail the effects of δ-conotoxin PVIA from the fish hunting cone snail Conus purpurascens on sodium currents in dissociated sympathetic neurons from the leopard frog Rana pipiens. We also compared this toxin’s effects with those of δ-conotoxin SVIE from Conus striatus, another piscivorous cone snail. d-PVIA slowed the time-course of inactivation of δ sodium currents and shifted the voltage-dependence of activation and steady-state inactivation to more hyperpolarized potentials. Similar, albeit more pronounced, effects were seen with d-SVIE. While the effects of d-PVIA were reversed by washing, those of d-SVIE were largely irreversible over the time-course of these experiments. The effects of d-PVIA could be suppressed by conditioning depolarizations in a voltage- and time-dependent manner, whereas the effects of d-SVIE were largely resistant to conditioning depolarizations. Last, in intact sympathetic nervous system preparations, d-PVIA inhibited evoked trains of compound action potentials. Many of these effects of d-PVIA and d-SVIE are remarkably similar to those of toxins that bind to site 3 on voltage-gated sodium channels.

Overexpression, purification, and pharmacological activity of a biosynthetically derived conopeptide

A high yielding fusion protein system based on the protein cytochrome b(5) has been used for the production of novel 13-residue acyclic conopeptide. This peptide, Mo1659, can be liberated from the carrier protein using CNBr cleavage and subsequent purification using RP-HPLC methods. The yield of isotopically enriched peptides is high, ranging from 3 to 4mg of purified peptide from a 500ml culture, indicating that this system can be widely used for peptide production. Biosynthetic Mo1659 is active on non-inactivating K(+) channel much like the natural Mo1659, despite the absence of C-terminal amidation. Heteronuclear NMR studies show that the peptide exists in a conformational equilibrium involving proline-10. To our knowledge this is the first report of the production of an isotopically (15)N/(13)C-enriched conopeptide.

Molecular interaction of δ-conotoxins with voltage-gated sodium channels

Various neurotoxic peptides modulate voltage-gated sodium (Na(V)) channels and thereby affect cellular excitability. Delta-conotoxins from predatory cone snails slow down inactivation of Na(V) channels, but their interaction site and mechanism of channel modulation are unknown. Here, we show that delta-conotoxin SVIE from Conus striatus interacts with a conserved hydrophobic triad (YFV) in the domain-4 voltage sensor of Na(V) channels. This site overlaps with that of the scorpion alpha-toxin Lqh-2, but not with the alpha-like toxin Lqh-3 site. Delta-SVIE functionally competes with Lqh-2, but exhibits strong cooperativity with Lqh-3, presumably by synergistically trapping the voltage sensor in its "on" position.

Total chemical synthesis and oxidative folding of delta-conotoxin PVIA containing an N-terminal propeptide

Small disulfide-rich peptides are translated as larger precursors typically containing an N-terminal prepro sequence. In this study, we investigated the role of a propeptide in the oxidative folding of an extremely hydrophobic delta-conotoxin, PVIA. delta-Conotoxin PVIA (delta-PVIA) is a 29-amino acid neurotoxin stabilized by three disulfide bridges. Previous folding studies on delta-conotoxins revealed that their poor folding properties resulted from their hydrophobicity. However, low folding yields of delta-PVIA could be improved by the presence of a nonionic detergent, which acted as a chemical chaperone. delta-PVIA provided an attractive model to investigate whether the hydrophilic propeptide region could function as an intramolecular chaperone. A 58-amino acid precursor for delta-PVIA (pro-PVIA), containing the N-terminal propeptide covalently attached to the mature conotoxin, was synthesized using native chemical ligation. Oxidative folding of pro-PVIA resulted in a very low accumulation of the correctly folded form, comparable to that for the mature conotoxin delta-PVIA. Our results are in accord with the relevant data previously observed for alpha- and omega-conotoxins, indicating that conotoxin prepro sequences are so-called class II propeptides, which are not directly involved in the oxidative folding. We hypothesize that these propeptide regions may be important for interactions with protein folding catalysts and sorting receptors during the secretory process.

Oxidative folding of conotoxins sharing an identical disulfide bridging framework

Conotoxins are short, disulfide-rich peptide neurotoxins produced in the venom of predatory marine cone snails. It is generally accepted that an estimated 100,000 unique conotoxins fall into only a handful of structural groups, based on their disulfide bridging frameworks. This unique molecular diversity poses a protein folding problem of relationships between hypervariability of amino acid sequences and mechanism(s) of oxidative folding. In this study, we present a comparative analysis of the folding properties of four conotoxins sharing an identical pattern of cysteine residues forming three disulfide bridges, but otherwise differing significantly in their primary amino acid sequence. Oxidative folding properties of M-superfamily conotoxins GIIIA, PIIIA, SmIIIA and RIIIK varied with respect to kinetics and thermodynamics. Based on rates for establishing the steady-state distribution of the folding species, two distinct folding mechanisms could be distinguished: first, rapid-collapse folding characterized by very fast, but low-yield accumulation of the correctly folded form; and second, slow-rearrangement folding resulting in higher accumulation of the properly folded form via the reshuffling of disulfide bonds within folding intermediates. Effects of changing the folding conditions indicated that the rapid-collapse and the slow-rearrangement mechanisms were mainly determined by either repulsive electrostatic or productive noncovalent interactions, respectively. The differences in folding kinetics for these two mechanisms were minimized in the presence of protein disulfide isomerase. Taken together, folding properties of conotoxins from the M-superfamily presented in this work and from the O-superfamily published previously suggest that conotoxin sequence diversity is also reflected in their folding properties, and that sequence information rather than a cysteine pattern determines the in vitro folding mechanisms of conotoxins.

A case study of 2,2-dimethylthiazolidine as locked cis proline amide bond: synthesis, NMR and molecular modeling studies of a δ-conotoxin EVIA peptide analog

The delta-conotoxin EVIA from the Conus ermineus venom, a recently characterized toxin, exhibits cis-trans isomerism of the Leu12-Pro13 bond associated with the triggering of its biological activity. In this paper we use the pseudoproline concept to target the presumed bioactive cis conformation. We report the design and the synthesis of loop 2 analogs from residue 8 to 18 containing either the cis-inducing Cys(PsiMe,MePro)13 unit or the natural proline residue. NMR studies in water and molecular modeling allowed us to identify the amide bond "locked" in a cis conformation for as in the suggested bioactive form of the natural toxin.