Solution structure of hanatoxin1, a gating modifier of voltage-dependent K(+) channels: common surface features of gating modifier toxins

An optimized CT-dense agent perfusion and micro-CT imaging protocol for chick embryo developmental stages

Compared to classical techniques of morphological analysis, micro-CT (μ-CT) has become an effective approach allowing rapid screening of morphological changes. In the present work, we aimed to provide an optimized micro-CT dense agent perfusion protocol and μ-CT guidelines for different stages of chick embryo cardiogenesis. Our study was conducted over a period of 10 embryonic days (Hamburger-Hamilton HH36) in chick embryo hearts. During the perfusion of the micro-CT dense agent at different developmental stages (HH19, HH24, HH27, HH29, HH31, HH34, HH35, and HH36), we demonstrated that durations and volumes of the injected contrast agent gradually increased with the heart developmental stages contrary to the flow rate that was unchanged during the whole experiment. Analysis of the CT imaging confirmed the efficiency of the optimized parameters of the heart perfusion.

Structural Conformation and Activity of Spider-Derived Inhibitory Cystine Knot Peptide Pn3a Are Modulated by pH

Numerous spider venom-derived gating modifier toxins exhibit conformational heterogeneity during purification by reversed-phase high-performance liquid chromatography (RP-HPLC). This conformational exchange is especially peculiar for peptides containing an inhibitor cystine knot motif, which confers excellent structural stability under conditions that are not conducive to disulfide shuffling. This phenomenon is often attributed to proline cis/trans isomerization but has also been observed in peptides that do not contain a proline residue. Pn3a is one such peptide forming two chromatographically distinguishable peaks that readily interconvert following the purification of either conformer. The nature of this exchange was previously uncharacterized due to the fast rate of conversion in solution, making isolation of the conformers impossible. In the present study, an N-terminal modification of Pn3a enabled the isolation of the individual conformers, allowing activity assays to be conducted on the individual conformers using electrophysiology. The conformers were analyzed separately by nuclear magnetic resonance spectroscopy (NMR) to study their structural differences. RP-HPLC and NMR were used to study the mechanism of exchange. The later-eluting conformer was the active conformer with a rigid structure that corresponds to the published structure of Pn3a, while NMR analysis revealed the earlier-eluting conformer to be inactive and disordered. The exchange was found to be pH-dependent, arising in acidic solutions, possibly due to reversible disruption and formation of intramolecular salt bridges. This study reveals the nature of non-proline conformational exchange observed in Pn3a and possibly other disulfide-rich peptides, highlighting that the structure and activity of some disulfide-stabilized peptides can be dramatically susceptible to disruption.

An optimized CT-dense agent perfusion and micro-CT imaging protocol for chick embryo developmental stages.. [DOI: 10.21203/rs.3.rs-2541863/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Compared to classical techniques of morphological analysis, micro-CT (µ-CT) has become an effective approach allowing rapid screening of morphological changes. In the present work, we aimed to provide an optimized µ-CT dense agent perfusion protocol and µ-CT guidelines for different stages of chick embryo cardiogenesis. Our study was conducted over a period of 10 embryonic days (Hamburger-Hamilton HH36) in chick embryo hearts. During the perfusion of the µ-CT dense agent at different developmental stages (HH19, HH24, HH27, HH29, HH31, HH34, HH35, and HH36), we demonstrated that durations and volumes of the injected contrast agent gradually increased with the heart developmental stages contrary to the flow rate that was unchanged during the whole experiment. Analysis of the CT imaging confirmed the efficiency of the optimized parameters of the heart perfusion.

In Silico Analysis of a Drosophila Parasitoid Venom Peptide Reveals Prevalence of the Cation-Polar-Cation Clip Motif in Knottin Proteins

As generalist parasitoid wasps, Leptopilina heterotoma are highly successful on many species of fruit flies of the genus Drosophila. The parasitoids produce specialized multi-strategy extracellular vesicle (EV)-like structures in their venom. Proteomic analysis identified several immunity-associated proteins, including the knottin peptide, LhKNOT, containing the structurally conserved inhibitor cysteine knot (ICK) fold, which is present in proteins from diverse taxa. Our structural and docking analysis of LhKNOT's 36-residue core knottin fold revealed that in addition to the knottin motif itself, it also possesses a Cation-Polar-Cation (CPC) clip. The CPC clip motif is thought to facilitate antimicrobial activity in heparin-binding proteins. Surprisingly, a majority of ICKs tested also possess the CPC clip motif, including 75 bona fide plant and arthropod knottin proteins that share high sequence and/or structural similarity with LhKNOT. Like LhKNOT and these other 75 knottin proteins, even the Drosophila Drosomycin antifungal peptide, a canonical target gene of the fly's Toll-NF-kappa B immune pathway, contains this CPC clip motif. Together, our results suggest a possible defensive function for the parasitoid LhKNOT. The prevalence of the CPC clip motif, intrinsic to the cysteine knot within the knottin proteins examined here, suggests that the resultant 3D topology is important for their biochemical functions. The CPC clip is likely a highly conserved structural motif found in many diverse proteins with reported heparin binding capacity, including amyloid proteins. Knottins are targets for therapeutic drug development, and insights into their structure-function relationships will advance novel drug design.

Scalable Biosynthetic Production of Knotted Peptides Enables ADME and Thermodynamic Folding Studies

Knotted peptides present a wealth of structurally diverse, biologically active molecules, with the inhibitor cystine knot/knottin class among the most ecologically common ones. Many of these natural products interact with extracellular targets such as voltage-gated ion channels with exquisite selectivity and potency, making them intriguing therapeutic modalities. Such compounds are often produced in low concentrations by intractable organisms, making structural and biological characterization challenging, which is frequently overcome by various expression strategies. Here, we sought to test a biosynthetic route for the expression and study of knotted peptides. We screened expression constructs for a biosynthesized knotted peptide to determine the most influential parameters for successful disulfide folding and used NMR spectroscopic fingerprinting to validate topological structures. We performed pharmacokinetic characterization, which indicated that the interlocking disulfide structure minimizes liabilities of linear peptide sequences, and propose a mechanism by which knotted peptides are cleared. We then developed an assay to monitor solution folding in real time, providing a strategy for studying the folding process during maturation, which provided direct evidence for the importance of backbone organization as the driving force for topology formation.

Chemical Synthesis of TFF3 Reveals Novel Mechanistic Insights and a Gut-Stable Metabolite

TFF3 regulates essential gastro- and neuroprotective functions, but its molecular mode of action remains poorly understood. Synthetic intractability and lack of reliable bioassays and validated receptors are bottlenecks for mechanistic and structure–activity relationship studies. Here, we report the chemical synthesis of TFF3 and its homodimer via native chemical ligation followed by oxidative folding. Correct folding was confirmed by NMR and circular dichroism, and TFF3 and its homodimer were not cytotoxic or hemolytic. TFF3, its homodimer, and the trefoil domain (TFF3_10-50) were susceptible to gastrointestinal degradation, revealing a gut-stable metabolite (TFF3_7-54; t_1/2 > 24 h) that retained its trefoil structure and antiapoptotic bioactivity. We tried to validate the putative TFF3 receptors CXCR4 and LINGO2, but neither TFF3 nor its homodimer displayed any activity up to 10 μM. The discovery of a gut-stable bioactive metabolite and reliable synthetic accessibility to TFF3 and its analogues are cornerstones for future molecular probe development and structure–activity relationship studies.

Peptide Toxins Targeting KV Channels

A number of peptide toxins isolated from animals target potassium ion (K⁺) channels. Many of them are particularly known to inhibit voltage-gated K⁺ (K_V) channels and are mainly classified into pore-blocking toxins or gating-modifier toxins. Pore-blocking toxins directly bind to the ion permeation pores of K_V channels, thereby physically occluding them. In contrast, gating-modifier toxins bind to the voltage-sensor domains of K_V channels, modulating their voltage-dependent conformational changes. These peptide toxins are useful molecular tools in revealing the structure-function relationship of K_V channels and have potential for novel treatments for diseases related to K_V channels. This review focuses on the inhibition mechanism of pore-blocking and gating-modifier toxins that target K_V channels.

Chemical Synthesis and NMR Solution Structure of Conotoxin GXIA from Conus geographus

Conotoxins are disulfide-rich peptides found in the venom of cone snails. Due to their exquisite potency and high selectivity for a wide range of voltage and ligand gated ion channels they are attractive drug leads in neuropharmacology. Recently, cone snails were found to have the capability to rapidly switch between venom types with different proteome profiles in response to predatory or defensive stimuli. A novel conotoxin, GXIA (original name G117), belonging to the I₃-subfamily was identified as the major component of the predatory venom of piscivorous Conus geographus. Using 2D solution NMR spectroscopy techniques, we resolved the 3D structure for GXIA, the first structure reported for the I₃-subfamily and framework XI family. The 32 amino acid peptide is comprised of eight cysteine residues with the resultant disulfide connectivity forming an ICK+1 motif. With a triple stranded β-sheet, the GXIA backbone shows striking similarity to several tarantula toxins targeting the voltage sensor of voltage gated potassium and sodium channels. Supported by an amphipathic surface, the structural evidence suggests that GXIA is able to embed in the membrane and bind to the voltage sensor domain of a putative ion channel target.

Chemical synthesis of human trefoil factor 1 (TFF1) and its homodimer provides novel insights into their mechanisms of action

TFF1 is a key peptide for gastrointestinal protection and repair. Its molecular mechanism of action remains poorly understood with synthetic intractability a recognised bottleneck. Here we describe the synthesis of TFF1 and its homodimer and their interactions with mucins and Helicobacter pylori. Synthetic access to TFF1 is an important milestone for probe and therapeutic development.

Mutational analysis of ProTx-I and the novel venom peptide Pe1b provide insight into residues responsible for selective inhibition of the analgesic drug target NaV1.7

Management of chronic pain presents a major challenge, since many currently available treatments lack efficacy and have problems such as addiction and tolerance. Loss of function mutations in the SCN9A gene lead to a congenital inability to feel pain, with no other sensory deficits aside from anosmia. SCN9A encodes the voltage-gated sodium (Na_V) channel 1.7 (Na_V1.7), which has been identified as a primary pain target. However, in developing Na_V1.7-targeted analgesics, extreme care must to be taken to avoid off-target activity on other Na_V subtypes that are critical for survival. Since spider venoms are an excellent source of Na_V channel modulators, we screened a panel of spider venoms to identify selective Na_V1.7 inhibitors. This led to identification of two novel Na_V modulating venom peptides (β/μ-theraphotoxin-Pe1a and β/μ-theraphotoxin-Pe1b (Pe1b) from the arboreal tarantula Phormingochilus everetti. A third peptide isolated from the tarantula Bumba pulcherrimaklaasi was identical to the well-known ProTx-I (β/ω-theraphotoxin-Tp1a) from the tarantula Thrixopelma pruriens. A tethered toxin (t-toxin)-based alanine scanning strategy was used to determine the Na_V1.7 pharmacophore of ProTx-I. We designed several ProTx-I and Pe1b analogues, and tested them for activity and Na_V channel subtype selectivity. Several analogues had improved potency against Na_V1.7, and altered specificity against other Na_V channels. These analogues provide a foundation for development of Pe1b as a lead molecule for therapeutic inhibition of Na_V1.7.

Jingzhaotoxin-X, a gating modifier of Kv4.2 and Kv4.3 potassium channels purified from the venom of the Chinese tarantula Chilobrachys jingzhao

Background

The tarantula Chilobrachys jingzhao is one of the largest venomous spiders in China. In previous studies, we purified and characterized at least eight peptides from C. jingzhao venom. In this report, we describe the purification and characterization of Jingzhaotoxin-X (JZTX-X), which selectively blocks Kv4.2 and Kv4.3 potassium channels.

Methods

JZTX-X was purified using a combination of cation-exchange HPLC and reverse-phase HPLC. The amino-acid sequence was determined by automated Edman degradation and confirmed by mass spectrometry (MS). Voltage-gated ion channel currents were recorded in HEK293t cells transiently transfected with a variety of ion channel constructs. In addition, the hyperalgesic activity of JZTX-X and the toxin´s effect on motor function were assessed in mice.

Results

JZTX-X contained 31 amino acids, with six cysteine residues that formed three disulfide bonds within an inhibitory cysteine knot (ICK) topology. In whole-cell voltage-clamp experiments, JZTX-X inhibited Kv4.2 and Kv4.3 potassium channels in a concentration- and voltage-dependent manner, without affecting other ion channels (Kv1.1, 1.2, 1.3, 2.1, delayed rectifier potassium channels, high- and low-voltage-activated Ca2+ channels, and voltage-gated sodium channels Nav1.5 and 1.7). JZTX-X also shifted the voltage-dependent channel activation to more depolarized potentials, whereas extreme depolarization caused reversible toxin binding to Kv4.2 channels. JZTX-X shifted the Kv4.2 and Kv4.3 activities towards a resting state, since at the resting potential the toxin completely inhibited the channels, even in the absence of an applied physical stimulus. Intrathecal or intraplantar injection of JZTX-X caused a long-lasting decrease in the mechanical nociceptive threshold (hyperalgesia) but had no effect on motor function as assessed in the rotarod test.

Conclusions

JZTX-X selectively suppresses Kv4.2 and Kv4.3 potassium channel activity in a concentration- and voltage-dependent manner and causes long-lasting mechanical hyperalgesia.

Venom-derived modulators of epilepsy-related ion channels

Epilepsy is characterised by spontaneous recurrent seizures that are caused by an imbalance between neuronal excitability and inhibition. Since ion channels play fundamental roles in the generation and propagation of action potentials as well as neurotransmitter release at a subset of excitatory and inhibitory synapses, their dysfunction has been linked to a wide variety of epilepsies. Indeed, these unique proteins are the major biological targets for antiepileptic drugs. Selective targeting of a specific ion channel subtype remains challenging for small molecules, due to the high level of homology among members of the same channel family. As a consequence, there is a growing trend to target ion channels with biologics. Venoms are the best known natural source of ion channel modulators, and venom peptides are increasingly recognised as potential therapeutics due to their high selectivity and potency gained through millions of years of evolutionary selection pressure. Here we describe the major ion channel families involved in the pathogenesis of various types of epilepsy, including voltage-gated Na⁺, K⁺, Ca²⁺ channels, Cys-loop receptors, ionotropic glutamate receptors and P2X receptors, and currently available venom-derived peptides that target these channel proteins. Although only a small number of venom peptides have successfully progressed to the clinic, there is reason to be optimistic about their development as antiepileptic drugs, notwithstanding the challenges associated with development of any class of peptide drug.

Marine Toxins Targeting Kv1 Channels: Pharmacological Tools and Therapeutic Scaffolds

Toxins from marine animals provide molecular tools for the study of many ion channels, including mammalian voltage-gated potassium channels of the Kv1 family. Selectivity profiling and molecular investigation of these toxins have contributed to the development of novel drug leads with therapeutic potential for the treatment of ion channel-related diseases or channelopathies. Here, we review specific peptide and small-molecule marine toxins modulating Kv1 channels and thus cover recent findings of bioactives found in the venoms of marine Gastropod (cone snails), Cnidarian (sea anemones), and small compounds from cyanobacteria. Furthermore, we discuss pivotal advancements at exploiting the interaction of κM-conotoxin RIIIJ and heteromeric Kv1.1/1.2 channels as prevalent neuronal Kv complex. RIIIJ's exquisite Kv1 subtype selectivity underpins a novel and facile functional classification of large-diameter dorsal root ganglion neurons. The vast potential of marine toxins warrants further collaborative efforts and high-throughput approaches aimed at the discovery and profiling of Kv1-targeted bioactives, which will greatly accelerate the development of a thorough molecular toolbox and much-needed therapeutics.

Weaponisation 'on the fly': Convergent recruitment of knottin and defensin peptide scaffolds into the venom of predatory assassin flies

Many arthropod venom peptides have potential as bioinsecticides, drug leads, and pharmacological tools due to their specific neuromodulatory functions. Assassin flies (Asilidae) are a family of predaceous dipterans that produce a unique and complex peptide-rich venom for killing insect prey and deterring predators. However, very little is known about the structure and function of their venom peptides. We therefore used an E. coli periplasmic expression system to express four disulfide-rich peptides that we previously reported to exist in venom of the giant assassin fly Dolopus genitalis. After purification, each recombinant peptide eluted from a C18 column at a position closely matching its natural counterpart, strongly suggesting adoption of the native tertiary fold. Injection of purified recombinant peptides into blowflies (Lucilia cuprina) and crickets (Acheta domestica) revealed that two of the four recombinant peptides, named rDg3b and rDg12, inhibited escape behaviour in a manner that was rapid in onset (<1 min) and reversible. Homonuclear NMR solution structures revealed that rDg3b and rDg12 adopt cystine-stabilised α/ß defensin and inhibitor cystine knot folds, respectively. Although the closest known homologues of rDg3b at the level of primary structure are dipteran antimicrobial peptides such as sapecin and lucifensin, a DALI search showed that the tertiary structure of rDg3b most closely resembles the K_V11.1-specific α-potassium channel toxin CnErg1 from venom of the scorpion Centruroides noxius. This is mainly due to the deletion of a large, unstructured loop between the first and second cysteine residues present in Dg3b homologues from non-asiloid, but not existing in asiloid, species. Patch-clamp electrophysiology experiments revealed that rDg3b shifts the voltage-dependence of K_V11.1 channel activation to more depolarised potentials, but has no effect on K_V1.3, K_V2.1, K_V10.1, K_Ca1.1, or the Drosophila Shaker channel. Although rDg12 shares the inhibitor cystine knot structure of many gating modifier toxins, rDg12 did not affect any of these K_V channel subtypes. Our results demonstrate that multiple disulfide-rich peptide scaffolds have been convergently recruited into asilid and other animal venoms, and they provide insight into the molecular evolution accompanying their weaponisation.

Spider Venom: Components, Modes of Action, and Novel Strategies in Transcriptomic and Proteomic Analyses

This review gives an overview on the development of research on spider venoms with a focus on structure and function of venom components and techniques of analysis. Major venom component groups are small molecular mass compounds, antimicrobial (also called cytolytic, or cationic) peptides (only in some spider families), cysteine-rich (neurotoxic) peptides, and enzymes and proteins. Cysteine-rich peptides are reviewed with respect to various structural motifs, their targets (ion channels, membrane receptors), nomenclature, and molecular binding. We further describe the latest findings concerning the maturation of antimicrobial, and cysteine-rich peptides that are in most known cases expressed as propeptide-containing precursors. Today, venom research, increasingly employs transcriptomic and mass spectrometric techniques. Pros and cons of venom gland transcriptome analysis with Sanger, 454, and Illumina sequencing are discussed and an overview on so far published transcriptome studies is given. In this respect, we also discuss the only recently described cross contamination arising from multiplexing in Illumina sequencing and its possible impacts on venom studies. High throughput mass spectrometric analysis of venom proteomes (bottom-up, top-down) are reviewed.

Ginsentides: Cysteine and Glycine-rich Peptides from the Ginseng Family with Unusual Disulfide Connectivity

Ginseng, a popular and valuable traditional medicine, has been used for centuries to maintain health and treat disease. Here we report the discovery and characterization of ginsentides, a novel family of cysteine and glycine-rich peptides derived from the three most widely-used ginseng species: Panax ginseng, Panax quinquefolius, and Panax notoginseng. Using proteomic and transcriptomic methods, we identified 14 ginsentides, TP1-TP14 which consist of 31-33 amino acids and whose expression profiles are species- and tissues-dependent. Ginsentides have an eight-cysteine motif typical of the eight-cysteine-hevein-like peptides (8C-HLP) commonly found in medicinal herbs, but lack a chitin-binding domain. Transcriptomic analysis showed that the three-domain biosynthetic precursors of ginsentides differ from known 8C-HLP precursors in architecture and the absence of a C-terminal protein-cargo domain. A database search revealed an additional 50 ginsentide-like precursors from both gymnosperms and angiosperms. Disulfide mapping and structure determination of the ginsentide TP1 revealed a novel disulfide connectivity that differs from the 8C-HLPs. The structure of ginsentide TP1 is highly compact, with the N- and C-termini topologically fixed by disulfide bonds to form a pseudocyclic structure that confers resistance to heat, proteolysis, and acid and serum-mediated degradation. Together, our results expand the chemical space of natural products found in ginseng and highlight the occurrence, distribution, disulfide connectivity, and precursor architectures of cysteine- and glycine-rich ginsentides as a class of novel non-chitin-binding, non-cargo-carrying 8C-HLPs.

Investigating the interaction of Grammostola rosea venom peptides and model lipid bilayers with solid-state NMR and electron microscopy techniques

Spider venom contains a number of small peptides that can control the gating properties of a wide range of ion channels with high affinity and specificity. These ion channels are responsible for coordination and control of many bodily functions such as transducing signals into sensory functions, smooth muscle contractions as well as serving as sensors in volume regulation. Hence, these peptides have been the topic of many research efforts in hopes that they can be used as biomedical therapeutics. Several peptides are known to control the gating properties of ion channels by involving the lipid membrane. GsMTx4, originally isolated from the Chilean Rose tarantula (Grammostola rosea), is known to selectively inhibit mechanosensitive ion channels by partitioning into the lipid bilayer. To further understand this indirect gating mechanism, we investigated the interactions between native GsAF2, VsTx1 and a synthetic form of GsMTx4 with model DMPC lipid bilayers using ³¹P solid-state NMR, ¹³C CP-MAS NMR, NS-TEM and cryo-TEM. The results reveal that these inhibitor cystine knot peptides perforate the DMPC lipid vesicles similarly with some subtle differences and ultimately create small spherical vesicles and anisotropic cylindrical and discoidal vesicles at concentrations near 1.0-1.5 mol% peptide. The anisotropic components align with their long axes along the NMR static B₀ magnetic field, a property that should be useful in future NMR structural investigations of these systems. These findings move us forward in our understanding of how these peptides bind and interact with the lipid bilayer.

The Penetration Depth for Hanatoxin Partitioning into the Membrane Hydrocarbon Core Measured with Neutron Reflectivity

Hanatoxin (HaTx) from spider venom works as an inhibitor of Kv2.1 channels, most likely by interacting with the voltage sensor (VS). However, the way in which this water-soluble peptide modifies the gating remains poorly understood as the VS is deeply embedded within the bilayer, although it would change its position depending on the membrane potential. To determine whether HaTx can indeed bind to the VS, the depth at which HaTx penetrates into the POPC membranes was measured with neutron reflectivity. Our results successfully demonstrate that HaTx penetrates into the membrane hydrocarbon core (∼9 Å from the membrane surface), not lying on the membrane-water interface as reported for another voltage sensor toxin (VSTx). This difference in penetration depth suggests that the two toxins fix the voltage sensors at different positions with respect to the membrane normal, thereby explaining their different inhibitory effects on the channels. In particular, results from MD simulations constrained by our penetration data clearly demonstrate an appropriate orientation for HaTx to interact with the membranes, which is in line with the biochemical information derived from stopped-flow analysis through delineation of the toxin-VS binding interface.

Gating modifier toxins isolated from spider venom: Modulation of voltage-gated sodium channels and the role of lipid membranes

Gating modifier toxins (GMTs) are venom-derived peptides isolated from spiders and other venomous creatures and modulate activity of disease-relevant voltage-gated ion channels and are therefore being pursued as therapeutic leads. The amphipathic surface profile of GMTs has prompted the proposal that some GMTs simultaneously bind to the cell membrane and voltage-gated ion channels in a trimolecular complex. Here, we examined whether there is a relationship among spider GMT amphipathicity, membrane binding, and potency or selectivity for voltage-gated sodium (Na_V) channels. We used NMR spectroscopy and in silico calculations to examine the structures and physicochemical properties of a panel of nine GMTs and deployed surface plasmon resonance to measure GMT affinity for lipids putatively found in proximity to Na_V channels. Electrophysiology was used to quantify GMT activity on Na_V1.7, an ion channel linked to chronic pain. Selectivity of the peptides was further examined against a panel of Na_V channel subtypes. We show that GMTs adsorb to the outer leaflet of anionic lipid bilayers through electrostatic interactions. We did not observe a direct correlation between GMT amphipathicity and affinity for lipid bilayers. Furthermore, GMT-lipid bilayer interactions did not correlate with potency or selectivity for Na_Vs. We therefore propose that increased membrane binding is unlikely to improve subtype selectivity and that the conserved amphipathic GMT surface profile is an adaptation that facilitates simultaneous modulation of multiple Na_Vs.

Animal Toxins Providing Insights into TRPV1 Activation Mechanism

Beyond providing evolutionary advantages, venoms offer unique research tools, as they were developed to target functionally important proteins and pathways. As a key pain receptor in the nociceptive pathway, transient receptor potential vanilloid 1 (TRPV1) of the TRP superfamily has been shown to be a target for several toxins, as a way of producing pain to deter predators. Importantly, TRPV1 is involved in thermoregulation, inflammation, and acute nociception. As such, toxins provide tools to understand TRPV1 activation and modulation, a critical step in advancing pain research and the development of novel analgesics. Indeed, the phytotoxin capsaicin, which is the spicy chemical in chili peppers, was invaluable in the original cloning and characterization of TRPV1. The unique properties of each subsequently characterized toxin have continued to advance our understanding of functional, structural, and biophysical characteristics of TRPV1. By building on previous reviews, this work aims to provide a comprehensive summary of the advancements made in TRPV1 research in recent years by employing animal toxins, in particular DkTx, RhTx, BmP01, Echis coloratus toxins, APHCs and HCRG21. We examine each toxin’s functional aspects, behavioral effects, and structural features, all of which have contributed to our current knowledge of TRPV1. We additionally discuss the key features of TRPV1’s outer pore domain, which proves to be the target of the currently discussed toxins.

APETx4, a Novel Sea Anemone Toxin and a Modulator of the Cancer-Relevant Potassium Channel KV10.1

The human ether-à-go-go channel (hEag1 or K_V10.1) is a cancer-relevant voltage-gated potassium channel that is overexpressed in a majority of human tumors. Peptides that are able to selectively inhibit this channel can be lead compounds in the search for new anticancer drugs. Here, we report the activity-guided purification and electrophysiological characterization of a novel K_V10.1 inhibitor from the sea anemone Anthopleura elegantissima. Purified sea anemone fractions were screened for inhibitory activity on K_V10.1 by measuring whole-cell currents as expressed in Xenopus laevis oocytes using the two-microelectrode voltage clamp technique. Fractions that showed activity on Kv10.1 were further purified by RP-HPLC. The amino acid sequence of the peptide was determined by a combination of MALDI- LIFT-TOF/TOF MS/MS and CID-ESI-FT-ICR MS/MS and showed a high similarity with APETx1 and APETx3 and was therefore named APETx4. Subsequently, the peptide was electrophysiologically characterized on K_V10.1. The selectivity of the toxin was investigated on an array of voltage-gated ion channels, including the cardiac human ether-à-go-go-related gene potassium channel (hERG or Kv11.1). The toxin inhibits K_V10.1 with an IC₅₀ value of 1.1 μM. In the presence of a similar toxin concentration, a shift of the activation curve towards more positive potentials was observed. Similar to the effect of the gating modifier toxin APETx1 on hERG, the inhibition of Kv10.1 by the isolated toxin is reduced at more positive voltages and the peptide seems to keep the channel in a closed state. Although the peptide also induces inhibitory effects on other K_V and Na_V channels, it exhibits no significant effect on hERG. Moreover, APETx4 induces a concentration-dependent cytotoxic and proapoptotic effect in various cancerous and noncancerous cell lines. This newly identified K_V10.1 inhibitor can be used as a tool to further characterize the oncogenic channel K_V10.1 or as a scaffold for the design and synthesis of more potent and safer anticancer drugs.

Small Scaffolds, Big Potential: Developing Miniature Proteins as Therapeutic Agents

Preclinical Research Miniature proteins are a class of oligopeptide characterized by their short sequence lengths and ability to adopt well-folded, three-dimensional structures. Because of their biomimetic nature and synthetic tractability, miniature proteins have been used to study a range of biochemical processes including fast protein folding, signal transduction, catalysis and molecular transport. Recently, miniature proteins have been gaining traction as potential therapeutic agents because their small size and ability to fold into defined tertiary structures facilitates their development as protein-based drugs. This research overview discusses emerging developments involving the use of miniature proteins as scaffolds to design novel therapeutics for the treatment and study of human disease. Specifically, this review will explore strategies to: (i) stabilize miniature protein tertiary structure; (ii) optimize biomolecular recognition by grafting functional epitopes onto miniature protein scaffolds; and (iii) enhance cytosolic delivery of miniature proteins through the use of cationic motifs that facilitate endosomal escape. These objectives are discussed not only to address challenges in developing effective miniature protein-based drugs, but also to highlight the tremendous potential miniature proteins hold for combating and understanding human disease. Drug Dev Res 78 : 268-282, 2017. © 2017 Wiley Periodicals, Inc.

Venom-derived peptide inhibitors of voltage-gated potassium channels

Voltage-gated potassium channels play a key role in human physiology and pathology. Reflecting their importance, numerous channelopathies have been characterised that arise from mutations in these channels or from autoimmune attack on the channels. Voltage-gated potassium channels are also the target of a broad range of peptide toxins from venomous organisms, including sea anemones, scorpions, spiders, snakes and cone snails; many of these peptides bind to the channels with high potency and selectivity. In this review we describe the various classes of peptide toxins that block these channels and illustrate the broad range of three-dimensional structures that support channel blockade. The therapeutic opportunities afforded by these peptides are also highlighted. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Modulatory features of the novel spider toxin μ-TRTX-Df1a isolated from the venom of the spider Davus fasciatus

BACKGROUND AND PURPOSE

Naturally occurring dysfunction of voltage-gated sodium (Na_V ) channels results in complex disorders such as chronic pain, making these channels an attractive target for new therapies. In the pursuit of novel Na_V modulators, we investigated spider venoms for new inhibitors of Na_V channels.

EXPERIMENTAL APPROACH

We used high-throughput screens to identify a Na_V modulator in venom of the spider Davus fasciatus. Further characterization of this venom peptide was undertaken using fluorescent and electrophysiological assays, molecular modelling and a rodent pain model.

KEY RESULTS

We identified a potent Na_V inhibitor named μ-TRTX-Df1a. This 34-residue peptide fully inhibited responses mediated by Na_V 1.7 endogenously expressed in SH-SY5Y cells. Df1a also inhibited voltage-gated calcium (Ca_V 3) currents but had no activity against the voltage-gated potassium (K_V 2) channel. The modelled structure of Df1a, which contains an inhibitor cystine knot motif, is reminiscent of the Na_V channel toxin ProTx-I. Electrophysiology revealed that Df1a inhibits all Na_V subtypes tested (hNa_V 1.1-1.7). Df1a also slowed fast inactivation of Na_V 1.1, Na_V 1.3 and Na_V 1.5 and modified the voltage-dependence of activation and inactivation of most of the Na_V subtypes. Df1a preferentially binds to the domain II voltage-sensor and has additional interactions with the voltage sensors domains III and IV, which probably explains its modulatory features. Df1a was analgesic in vivo, reversing the spontaneous pain behaviours induced by the Na_V activator OD1.

CONCLUSION AND IMPLICATIONS

μ-TRTX-Df1a shows potential as a new molecule for the development of drugs to treat pain disorders mediated by voltage-gated ion channels.

Gating modifier toxin interactions with ion channels and lipid bilayers: Is the trimolecular complex real?

Spider peptide toxins have attracted attention because of their ability to target voltage-gated ion channels, which are involved in several pathologies including chronic pain and some cardiovascular conditions. A class of these peptides acts by modulating the gating mechanism of voltage-gated ion channels and are thus called gating modifier toxins (GMTs). In addition to their interactions with voltage-gated ion channels, some GMTs have affinity for lipid bilayers. This review discusses the potential importance of the cell membrane on the mode of action of GMTs. We propose that peptide-membrane interactions can anchor GMTs at the cell surface, thereby increasing GMT concentration in the vicinity of the channel binding site. We also propose that modulating peptide-membrane interactions might be useful for increasing the therapeutic potential of spider toxins. Furthermore, we explore the advantages and limitations of the methodologies currently used to examine peptide-membrane interactions. Although GMT-lipid membrane binding does not appear to be a requirement for the activity of all GMTs, it is an important feature, and future studies with GMTs should consider the trimolecular peptide-lipid membrane-channel complex. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Measurement of Hanatoxin-Induced Membrane Thinning with Lamellar X-ray Diffraction

Membrane perturbation induced by cysteine-rich peptides is a crucial biological phenomenon but scarcely investigated, in particular with effective biophysical-chemical methodologies. Hanatoxin (HaTx), a 35-residue polypeptide from spider venom, works as an inhibitor of drk1 (Kv2.1) channels, most likely by interacting with the voltage-sensor. However, how this water-soluble peptide modifies the gating remains poorly understood, as the voltage sensor was proposed to be deeply embedded within the bilayer. To see how HaTx interacts with phospholipid bilayers, we observe the toxin-induced perturbation on POPC/DOPG-membranes through measurements of the change in membrane thickness. Lamellar X-ray diffraction (LXD) was applied on stacked planar bilayers in the near-fully hydrated state. The results provide quantitative evidence for the membrane thinning in a concentration-dependent manner, leading to novel and direct combinatory approaches by discovering how to investigate such a biologically relevant interaction between gating-modifier toxins and phospholipid bilayers.

Hanatoxin inserts into phospholipid membranes without pore formation

Hanatoxin (HaTx), a 35-residue polypeptide from spider venom, functions as an inhibitor of Kv2.1 channels by interacting with phospholipids prior to affecting the voltage-sensor. However, how this water-soluble peptide modifies the gating remains poorly understood, as the voltage-sensor is deeply embedded within the bilayer. To determine how HaTx interacts with phospholipid bilayers, in this study, we examined the toxin-induced partitioning of liposomal membranes. HPLC-results from high-speed spin-down vesicles with HaTx demonstrated direct binding. Dynamic light scattering (DLS) and leakage assay results further indicated that neither membrane pores nor membrane fragmentations were observed in the presence of HaTx. To clarify the binding details, Langmuir trough experiments were performed with phospholipid monolayers by mimicking the external leaflet of membrane bilayers, indicating the involvement of acyl chains in such interactions between HaTx and phospholipids. Our current study thus describes the interaction pattern of HaTx with vesicle membranes, defining a membrane-partitioning mechanism for peptide insertion involving the membrane hydrocarbon core without pore formation.

Pharmacological characterisation of the highly NaV1.7 selective spider venom peptide Pn3a

Human genetic studies have implicated the voltage-gated sodium channel NaV1.7 as a therapeutic target for the treatment of pain. A novel peptide, μ-theraphotoxin-Pn3a, isolated from venom of the tarantula Pamphobeteus nigricolor, potently inhibits NaV1.7 (IC50 0.9 nM) with at least 40-1000-fold selectivity over all other NaV subtypes. Despite on-target activity in small-diameter dorsal root ganglia, spinal slices, and in a mouse model of pain induced by NaV1.7 activation, Pn3a alone displayed no analgesic activity in formalin-, carrageenan- or FCA-induced pain in rodents when administered systemically. A broad lack of analgesic activity was also found for the selective NaV1.7 inhibitors PF-04856264 and phlotoxin 1. However, when administered with subtherapeutic doses of opioids or the enkephalinase inhibitor thiorphan, these subtype-selective NaV1.7 inhibitors produced profound analgesia. Our results suggest that in these inflammatory models, acute administration of peripherally restricted NaV1.7 inhibitors can only produce analgesia when administered in combination with an opioid.

Interaction site for the inhibition of tarantula Jingzhaotoxin-XI on voltage-gated potassium channel Kv2.1

Jingzhaotoxin-XI (JZTX-XI) is a 34-residue peptide from the Chinese tarantula Chilobrachys jingzhao venom that potently inhibits both voltage-gated sodium channel Nav1.5 and voltage-gated potassium channel Kv2.1. In the present study, we further showed that JZTX-XI blocked Kv2.1 currents with the IC₅₀ value of 0.39 ± 0.06 μM. JZTX-XI significantly shifted the current-voltage (I-V) curves and normalized conductance-voltage (G-V) curves of Kv2.1 channel to more depolarized voltages. Ala-scanning mutagenesis analyses demonstrated that mutants I273A, F274A, and E277A reduced toxin binding affinity by 10-, 16-, and 18-fold, respectively, suggesting that three common residues (I273, F274, E277) in the Kv2.1 S3b segment contribute to the formation of JZTX-XI receptor site, and the acidic residue Glu at the position 277 in Kv2.1 is the most important residue for JZTX-XI sensitivity. A single replacement of E277 with Asp(D) increased toxin inhibitory activity. These results establish that JZTX-XI inhibits Kv2.1 activation by trapping the voltage sensor in the rested state through a similar mechanism to that of HaTx1, but these two toxins have small differences in the most crucial molecular determinant. Furthermore, the in-depth investigation of the subtle differences in molecular determinants may be useful for increasing our understanding of the molecular details regarding toxin-channel interactions.

Peptidomics of Acanthoscurria gomesiana spider venom reveals new toxins with potential antimicrobial activity

Acanthoscurria gomesiana is a Brazilian spider from the Theraphosidae family inhabiting regions of Southeastern Brazil. Potent antimicrobial peptides as gomesin and acanthoscurrin have been discovered from the spider hemolymph in previous works. Spider venoms are also recognized as sources of biologically active peptides, however the venom peptidome of A. gomesiana remained unexplored to date. In this work, a MS-based workflow was applied to the investigation of the spider venom peptidome. Data-independent and data-dependent LC-MS/MS acquisitions of intact peptides and of peptides submitted to multiple enzyme digestions, followed by automated chromatographic alignment, de novo analysis, database and homology searches with manual validations showed that the venom is composed by <165 features, with masses ranging from 0.4-15.8kDa. From digestions, 135 peptides were identified from 17 proteins, including three new mature peptides: U1-TRTX-Agm1a, U1-TRTX-Agm2a and U1-TRTX-Agm3a, containing 3, 4 and 3 disulfide bonds, respectively. The toxins U1-TRTX-Agm1a differed by only one amino acid from U1-TRTX-Ap1a from A. paulensis and U1-TRTX-Agm2a was derived from the genicutoxin-D1 precursor from A. geniculata. These toxins have potential applications as antimicrobial agents, as the peptide fraction of A. gomesiana showed activity against Escherichia coli, Enterobacter cloacae and Candida albicans strains. MS data are available via ProteomeXchange Consortium with identifier PXD003884.

BIOLOGICAL SIGNIFICANCE

Biological fluids of the Acanthoscurria gomesiana spider are sources of active molecules, as is the case of antimicrobial peptides and acylpolyamines found in the hemolymphs. The venom is also a potential source of toxins with pharmacological and biotechnological applications. However, to our knowledge no A. gomesiana venom toxin structure has been determined to date. Using a combination of high resolution mass spectrometry, transcriptomics and bioinformatics, we employed a workflow to fully sequence, determine the number of disulfide bonds of mature peptides and we found new potential antimicrobial peptides. This workflow is suitable for complete peptide toxin sequencing when handling limited amount of venom samples and can accelerate the discovery of peptides with potential biotechnological applications.

Engineering Highly Potent and Selective Microproteins against Nav1.7 Sodium Channel for Treatment of Pain

The prominent role of voltage-gated sodium channel 1.7 (Nav1.7) in nociception was revealed by remarkable human clinical and genetic evidence. Development of potent and subtype-selective inhibitors of this ion channel is crucial for obtaining therapeutically useful analgesic compounds. Microproteins isolated from animal venoms have been identified as promising therapeutic leads for ion channels, because they naturally evolved to be potent ion channel blockers. Here, we report the engineering of highly potent and selective inhibitors of the Nav1.7 channel based on tarantula ceratotoxin-1 (CcoTx1). We utilized a combination of directed evolution, saturation mutagenesis, chemical modification, and rational drug design to obtain higher potency and selectivity to the Nav1.7 channel. The resulting microproteins are highly potent (IC50 to Nav1.7 of 2.5 nm) and selective. We achieved 80- and 20-fold selectivity over the closely related Nav1.2 and Nav1.6 channels, respectively, and the IC50 on skeletal (Nav1.4) and cardiac (Nav1.5) sodium channels is above 3000 nm The lead molecules have the potential for future clinical development as novel therapeutics in the treatment of pain.

Molecular Interactions between Tarantula Toxins and Low-Voltage-Activated Calcium Channels

Few gating-modifier toxins have been reported to target low-voltage-activated (LVA) calcium channels, and the structural basis of toxin sensitivity remains incompletely understood. Studies of voltage-gated potassium (Kv) channels have identified the S3b–S4 “paddle motif,” which moves at the protein-lipid interface to drive channel opening, as the target for these amphipathic neurotoxins. Voltage-gated calcium (Cav) channels contain four homologous voltage sensor domains, suggesting multiple toxin binding sites. We show here that the S3–S4 segments within Cav3.1 can be transplanted into Kv2.1 to examine their individual contributions to voltage sensing and pharmacology. With these results, we now have a more complete picture of the conserved nature of the paddle motif in all three major voltage-gated ion channel types (Kv, Nav, and Cav). When screened with tarantula toxins, the four paddle sequences display distinct toxin binding properties, demonstrating that gating-modifier toxins can bind to Cav channels in a domain specific fashion. Domain III was the most commonly and strongly targeted, and mutagenesis revealed an acidic residue that is important for toxin binding. We also measured the lipid partitioning strength of all toxins tested and observed a positive correlation with their inhibition of Cav3.1, suggesting a key role for membrane partitioning.

Structural insights into the mechanism of activation of the TRPV1 channel by a membrane-bound tarantula toxin

Venom toxins are invaluable tools for exploring the structure and mechanisms of ion channels. Here, we solve the structure of double-knot toxin (DkTx), a tarantula toxin that activates the heat-activated TRPV1 channel. We also provide improved structures of TRPV1 with and without the toxin bound, and investigate the interactions of DkTx with the channel and membranes. We find that DkTx binds to the outer edge of the external pore of TRPV1 in a counterclockwise configuration, using a limited protein-protein interface and inserting hydrophobic residues into the bilayer. We also show that DkTx partitions naturally into membranes, with the two lobes exhibiting opposing energetics for membrane partitioning and channel activation. Finally, we find that the toxin disrupts a cluster of hydrophobic residues behind the selectivity filter that are critical for channel activation. Collectively, our findings reveal a novel mode of toxin-channel recognition that has important implications for the mechanism of thermosensation.

Membrane/Toxin Interaction Energetics via Serial Multiscale Molecular Dynamics Simulations

Computing free energies of complex biomolecular systems via atomistic (AT) molecular dynamics (MD) simulations remains a challenge due to the need for adequate sampling and convergence. Recent coarse-grained (CG) methodology allows simulations of significantly larger systems (∼10(6) to 10(8) atoms) over longer (μs/ms) time scales. Such CG models appear to be capable of making semiquantitative predictions. However, their ability to reproduce accurate thermodynamic quantities remains uncertain. We have recently used CG MD simulations to compute the potential of mean force (PMF) or free energy profile of a small peptide toxin interacting with a lipid bilayer along a 1D reaction coordinate. The toxin studied was VSTx1 (Voltage Sensor Toxin 1) from spider venom which inhibits the archeabacterial voltage-gated potassium (Kv) channel KvAP by binding to the voltage-sensor (VS) domains. Here, we re-estimate this PMF profile using (i) AT MD simulations with explicit membrane and solvent and (ii) an implicit membrane and solvent (generalized Born; GBIM) model where only the peptide was explicit. We used the CG MD free energy simulations to guide the setup of the corresponding AT MD simulations. The aim was to avoid local minima in the AT simulations which would be difficult over shorter AT time scales. A cross-comparison of the PMF profiles revealed a conserved topology, although there were differences in the magnitude of the free energies. The CG and AT simulations predicted a membrane/water interface free energy well of -27 and -23 kcal/mol, respectively (with respect to water). The GBIM model, however, gave a reduced interfacial free energy well (-12 kcal/mol). In addition, the CG and GBIM models predicted a free energy barrier of +61 and +96 kcal/mol, respectively, for positioning the toxin at the center of the bilayer, which was considerably smaller in the AT simulations (+26 kcal/mol). Thus, we present a framework for serially combining CG and AT simulations to estimate the free energy of peptide/membrane interactions. Such approaches for combining simulations at different levels of granularity will become increasingly important in future studies of complex membrane/protein systems.

Computational Studies of Venom Peptides Targeting Potassium Channels

Small peptides isolated from the venom of animals are potential scaffolds for ion channel drug discovery. This review article mainly focuses on the computational studies that have advanced our understanding of how various toxins interfere with the function of K⁺ channels. We introduce the computational tools available for the study of toxin-channel interactions. We then discuss how these computational tools have been fruitfully applied to elucidate the mechanisms of action of a wide range of venom peptides from scorpions, spiders, and sea anemone.

Structural basis for the inhibition of voltage-dependent K+ channel by gating modifier toxin

Voltage-dependent K⁺ (K_v) channels play crucial roles in nerve and muscle action potentials. Voltage-sensing domains (VSDs) of K_v channels sense changes in the transmembrane potential, regulating the K⁺-permeability across the membrane. Gating modifier toxins, which have been used for the functional analyses of K_v channels, inhibit K_v channels by binding to VSD. However, the structural basis for the inhibition remains elusive. Here, fluorescence and NMR analyses of the interaction between VSD derived from K_vAP channel and its gating modifier toxin, VSTx1, indicate that VSTx1 recognizes VSD under depolarized condition. We identified the VSD-binding residues of VSTx1 and their proximal residues of VSD by the cross-saturation (CS) and amino acid selective CS experiments, which enabled to build a docking model of the complex. These results provide structural basis for the specific binding and inhibition of K_v channels by gating modifier toxins.

Weaponization of a Hormone: Convergent Recruitment of Hyperglycemic Hormone into the Venom of Arthropod Predators

Arthropod venoms consist primarily of peptide toxins that are injected into their prey with devastating consequences. Venom proteins are thought to be recruited from endogenous body proteins and mutated to yield neofunctionalized toxins with remarkable affinity for specific subtypes of ion channels and receptors. However, the evolutionary history of venom peptides remains poorly understood. Here we show that a neuropeptide hormone has been convergently recruited into the venom of spiders and centipedes and evolved into a highly stable toxin through divergent modification of the ancestral gene. High-resolution structures of representative hormone-derived toxins revealed they possess a unique structure and disulfide framework and that the key structural adaptation in weaponization of the ancestral hormone was loss of a C-terminal α helix, an adaptation that occurred independently in spiders and centipedes. Our results raise a new paradigm for toxin evolution and highlight the value of structural information in providing insight into protein evolution.

Tarantula toxins use common surfaces for interacting with Kv and ASIC ion channels

Tarantula toxins that bind to voltage-sensing domains of voltage-activated ion channels are thought to partition into the membrane and bind to the channel within the bilayer. While no structures of a voltage-sensor toxin bound to a channel have been solved, a structural homolog, psalmotoxin (PcTx1), was recently crystalized in complex with the extracellular domain of an acid sensing ion channel (ASIC). In the present study we use spectroscopic, biophysical and computational approaches to compare membrane interaction properties and channel binding surfaces of PcTx1 with the voltage-sensor toxin guangxitoxin (GxTx-1E). Our results show that both types of tarantula toxins interact with membranes, but that voltage-sensor toxins partition deeper into the bilayer. In addition, our results suggest that tarantula toxins have evolved a similar concave surface for clamping onto α-helices that is effective in aqueous or lipidic physical environments.

Structural interactions of a voltage sensor toxin with lipid membranes

Protein toxins from tarantula venom alter the activity of diverse ion channel proteins, including voltage, stretch, and ligand-activated cation channels. Although tarantula toxins have been shown to partition into membranes, and the membrane is thought to play an important role in their activity, the structural interactions between these toxins and lipid membranes are poorly understood. Here, we use solid-state NMR and neutron diffraction to investigate the interactions between a voltage sensor toxin (VSTx1) and lipid membranes, with the goal of localizing the toxin in the membrane and determining its influence on membrane structure. Our results demonstrate that VSTx1 localizes to the headgroup region of lipid membranes and produces a thinning of the bilayer. The toxin orients such that many basic residues are in the aqueous phase, all three Trp residues adopt interfacial positions, and several hydrophobic residues are within the membrane interior. One remarkable feature of this preferred orientation is that the surface of the toxin that mediates binding to voltage sensors is ideally positioned within the lipid bilayer to favor complex formation between the toxin and the voltage sensor.

Structure of membrane-active toxin from crab spider Heriaeus melloteei suggests parallel evolution of sodium channel gating modifiers in Araneomorphae and Mygalomorphae

We present a structural and functional study of a sodium channel activation inhibitor from crab spider venom. Hm-3 is an insecticidal peptide toxin consisting of 35 amino acid residues from the spider Heriaeus melloteei (Thomisidae). We produced Hm-3 recombinantly in Escherichia coli and determined its structure by NMR spectroscopy. Typical for spider toxins, Hm-3 was found to adopt the so-called "inhibitor cystine knot" or "knottin" fold stabilized by three disulfide bonds. Its molecule is amphiphilic with a hydrophobic ridge on the surface enriched in aromatic residues and surrounded by positive charges. Correspondingly, Hm-3 binds to both neutral and negatively charged lipid vesicles. Electrophysiological studies showed that at a concentration of 1 μm Hm-3 effectively inhibited a number of mammalian and insect sodium channels. Importantly, Hm-3 shifted the dependence of channel activation to more positive voltages. Moreover, the inhibition was voltage-dependent, and strong depolarizing prepulses attenuated Hm-3 activity. The toxin is therefore concluded to represent the first sodium channel gating modifier from an araneomorph spider and features a "membrane access" mechanism of action. Its amino acid sequence and position of the hydrophobic cluster are notably different from other known gating modifiers from spider venom, all of which are described from mygalomorph species. We hypothesize parallel evolution of inhibitor cystine knot toxins from Araneomorphae and Mygalomorphae suborders.

Normal mode dynamics of voltage-gated K(+) channels: gating principle, opening mechanism, and inhibition

Voltage-dependent potassium channels open in response to changes in membrane potential and become partially inactivated upon binding of inhibitors. Here we calculate normal mode motion of two voltage-dependent K(+) channels, KvAP and Shaker, and their complexes with inhibitors and address the gating principle, opening mechanism, and inhibition. The normal modes indicate that pore expansion and channel opening is correlated with a displacement of the arginine gating charges and a tilting of the voltage-sensor paddles. Normal modes of Shaker in complex with agitoxin, which blocks the central pore, do not display significantly altered paddle tilting and pore expansion. In contrast, normal modes of Shaker in complex with hanatoxin, which binds to the voltage sensor paddle, display decreased paddle tilting and pore expansion. This study presents a unified motion for the gating principle and channel opening, and offers insight into the voltage sensor paddle motion and its inhibition.

Pathogen-inspired drug delivery to the central nervous system

For as long as the human blood-brain barrier (BBB) has been evolving to exclude bloodborne agents from the central nervous system (CNS), pathogens have adopted a multitude of strategies to bypass it. Some pathogens, notably viruses and certain bacteria, enter the CNS in whole form, achieving direct physical passage through endothelial or neuronal cells to infect the brain. Other pathogens, including bacteria and multicellular eukaryotic organisms, secrete toxins that preferentially interact with specific cell types to exert a broad range of biological effects on peripheral and central neurons. In this review, we will discuss the directed mechanisms that viruses, bacteria, and the toxins secreted by higher order organisms use to enter the CNS. Our goal is to identify ligand-mediated strategies that could be used to improve the brain-specific delivery of engineered nanocarriers, including polymers, lipids, biologically sourced materials, and imaging agents.

From foe to friend: using animal toxins to investigate ion channel function

Ion channels are vital contributors to cellular communication in a wide range of organisms, a distinct feature that renders this ubiquitous family of membrane-spanning proteins a prime target for toxins found in animal venom. For many years, the unique properties of these naturally occurring molecules have enabled researchers to probe the structural and functional features of ion channels and to define their physiological roles in normal and diseased tissues. To illustrate their considerable impact on the ion channel field, this review will highlight fundamental insights into toxin-channel interactions and recently developed toxin screening methods and practical applications of engineered toxins.

Isolation, synthesis and characterization of ω-TRTX-Cc1a, a novel tarantula venom peptide that selectively targets L-type Cav channels

Spider venoms are replete with peptidic ion channel modulators, often with novel subtype selectivity, making them a rich source of pharmacological tools and drug leads. In a search for subtype-selective blockers of voltage-gated calcium (CaV) channels, we isolated and characterized a novel 39-residue peptide, ω-TRTX-Cc1a (Cc1a), from the venom of the tarantula Citharischius crawshayi (now Pelinobius muticus). Cc1a is 67% identical to the spider toxin ω-TRTX-Hg1a, an inhibitor of CaV2.3 channels. We assembled Cc1a using a combination of Boc solid-phase peptide synthesis and native chemical ligation. Oxidative folding yielded two stable, slowly interconverting isomers. Cc1a preferentially inhibited Ba(2+) currents (IBa) mediated by L-type (CaV1.2 and CaV1.3) CaV channels heterologously expressed in Xenopus oocytes, with half-maximal inhibitory concentration (IC50) values of 825nM and 2.24μM, respectively. In rat dorsal root ganglion neurons, Cc1a inhibited IBa mediated by high voltage-activated CaV channels but did not affect low voltage-activated T-type CaV channels. Cc1a exhibited weak activity at NaV1.5 and NaV1.7 voltage-gated sodium (NaV) channels stably expressed in mammalian HEK or CHO cells, respectively. Experiments with modified Cc1a peptides, truncated at the N-terminus (ΔG1-E5) or C-terminus (ΔW35-V39), demonstrated that the N- and C-termini are important for voltage-gated ion channel modulation. We conclude that Cc1a represents a novel pharmacological tool for probing the structure and function of L-type CaV channels.