Isolation, amino acid sequence and functional assays of SGTx1. The first toxin purified from the venom of the spider scodra griseipes

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.

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.

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.

Arthropod toxins acting on neuronal potassium channels

Arthropod venoms are a rich mixture of biologically active compounds exerting different physiological actions across diverse phyla and affecting multiple organ systems including the central nervous system. Venom compounds can inhibit or activate ion channels, receptors and transporters with high specificity and affinity providing essential insights into ion channel function. In this review, we focus on arthropod toxins (scorpions, spiders, bees and centipedes) acting on neuronal potassium channels. A brief description of the K⁺ channels classification and structure is included and a compendium of neuronal K⁺ channels and the arthropod toxins that modify them have been listed. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

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.'

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.

Computational methods of studying the binding of toxins from venomous animals to biological ion channels: theory and applications

The discovery of new drugs that selectively block or modulate ion channels has great potential to provide new treatments for a host of conditions. One promising avenue revolves around modifying or mimicking certain naturally occurring ion channel modulator toxins. This strategy appears to offer the prospect of designing drugs that are both potent and specific. The use of computational modeling is crucial to this endeavor, as it has the potential to provide lower cost alternatives for exploring the effects of new compounds on ion channels. In addition, computational modeling can provide structural information and theoretical understanding that is not easily derivable from experimental results. In this review, we look at the theory and computational methods that are applicable to the study of ion channel modulators. The first section provides an introduction to various theoretical concepts, including force-fields and the statistical mechanics of binding. We then look at various computational techniques available to the researcher, including molecular dynamics, brownian dynamics, and molecular docking systems. The latter section of the review explores applications of these techniques, concentrating on pore blocker and gating modifier toxins of potassium and sodium channels. After first discussing the structural features of these channels, and their modes of block, we provide an in-depth review of past computational work that has been carried out. Finally, we discuss prospects for future developments in the field.

Spider peptide toxins as leads for drug development

Venomous animals use a highly complex cocktails of proteins, peptides and small molecules to subdue and kill their prey. As such, venoms represent highly valuable combinatorial peptide libraries, displaying an extensive range of pharmacological activities, honed by natural selection. Modern analytical technologies enable us to take full advantage of this vast pharmacological cornucopia in the hunt for novel drug leads. Spider venoms represent a resource of several million peptides, which selectively target specific subtypes of ion channels. Structure-function studies of spider toxins are leading not only to the discovery of novel molecules, but also to novel therapeutic routes for cardiovascular diseases, cancer, neuromuscular diseases, pain and to a variety of other pathological conditions. This review presents an overview of spider peptide toxins as candidates for therapeutics and focuses on their applications in the discovery of novel mechanisms of analgesia.

Effect of gating modifier toxins on membrane thickness: implications for toxin effect on gramicidin and mechanosensitive channels

Various gating modifier toxins partition into membranes and interfere with the gating mechanisms of biological ion channels. For example, GsMTx4 potentiates gramicidin and several bacterial mechanosensitive channels whose gating kinetics are sensitive to mechanical properties of the membrane, whereas binding of HpTx2 shifts the voltage-activity curve of the voltage-gated potassium channel Kv4.2 to the right. The detailed process by which the toxin partitions into membranes has been difficult to probe using molecular dynamics due to the limited time scale accessible. Here we develop a protocol that allows the spontaneous assembly of a polypeptide toxin into membranes in atomistic molecular dynamics simulations of tens of nanoseconds. The protocol is applied to GsMTx4 and HpTx2. Both toxins, released in water at the start of the simulation, spontaneously bind into the lipid bilayer within 50 ns, with their hydrophobic patch penetrated into the bilayer beyond the phosphate groups of the lipids. It is found that the bilayer is about 2 Å thinner upon the binding of a GsMTx4 monomer. Such a thinning effect of GsMTx4 on membranes may explain its potentiation effect on gramicidin and mechanosensitive channels.

Binding of hanatoxin to the voltage sensor of Kv2.1

Hanatoxin 1 (HaTx1) is a polypeptide toxin isolated from spider venoms. HaTx1 inhibits the voltage-gated potassium channel kv2.1 potently with nanomolar affinities. Its receptor site has been shown to contain the S3b-S4a paddle of the voltage sensor (VS). Here, the binding of HaTx1 to the VSs of human Kv2.1 in the open and resting states are examined using a molecular docking method and molecular dynamics. Molecular docking calculations predict two distinct binding modes for the VS in the resting state. In the two binding modes, the toxin binds the S3b-S4a from S2 and S3 helices, or from S1 and S4 helices. Both modes are found to be stable when embedded in a lipid bilayer. Only the mode in which the toxin binds the S3b-S4a paddle from S2 and S3 helices is consistent with mutagenesis experiments, and considered to be correct. The toxin is then docked to the VS in the open state, and the toxin-VS interactions are found to be less favorable. Computational mutagenesis calculations performed on F278R and E281K mutant VSs show that the mutations may reduce toxin binding affinity by weakening the non-bonded interactions between the toxin and the VS. Overall, our calculations reproduce a wide range of experimental data, and suggest that HaTx1 binds to the S3b-S4a paddle of Kv2.1 from S2 and S3 helices.

Molecular determinants for the tarantula toxin jingzhaotoxin-I interacting with potassium channel Kv2.1

With high binding affinity and distinct pharmacological functions, animal toxins are powerful ligands to investigate the structure-function relationships of voltage-gated ion channels. Jingzhaotoxin-I (JZTX-I) is an important neurotoxin from the tarantula Chilobrachys jingzhao venom that inhibits both sodium and potassium channels. In our previous work, JZTX-I, as a gating modifier, is able to inhibit activation of the potassium channel subtype Kv2.1. However, its binding site on Kv2.1 remains unknown. In this study, using Ala-scanning mutagenesis strategy, we demonstrated that four residues (I273, F274, E277, and K280) in S3b-S4 motif contributed to the formation of JZTX-I binding site. The mutations I273A, F274A, E277A, and K280A reduced toxin binding affinity by 6-, 10-, 8-, and 7-fold, respectively. Taken together with our previous data that JZTX-I accelerated channel deactivation, these results suggest that JZTX-I inhibits Kv2.1 activation by docking onto the voltage sensor paddle and trapping the voltage sensor in the closed state.

Towards therapeutic applications of arthropod venom k(+)-channel blockers in CNS neurologic diseases involving memory acquisition and storage

Potassium channels are the most heterogeneous and widely distributed group of ion channels and play important functions in all cells, in both normal and pathological mechanisms, including learning and memory processes. Being fundamental for many diverse physiological processes, K⁺-channels are recognized as potential therapeutic targets in the treatment of several Central Nervous System (CNS) diseases, such as multiple sclerosis, Parkinson's and Alzheimer's diseases, schizophrenia, HIV-1-associated dementia, and epilepsy. Blockers of these channels are therefore potential candidates for the symptomatic treatment of these neuropathies, through their neurological effects. Venomous animals have evolved a wide set of toxins for prey capture and defense. These compounds, mainly peptides, act on various pharmacological targets, making them an innumerable source of ligands for answering experimental paradigms, as well as for therapeutic application. This paper provides an overview of CNS K⁺-channels involved in memory acquisition and storage and aims at evaluating the use of highly selective K⁺-channel blockers derived from arthropod venoms as potential therapeutic agents for CNS diseases involving learning and memory mechanisms.

Solution structure of kurtoxin: a gating modifier selective for Cav3 voltage-gated Ca(2+) channels

Kurtoxin is a 63-amino acid polypeptide isolated from the venom of the South African scorpion Parabuthus transvaalicus. It is the first and only peptide ligand known to interact with Cav3 (T-type) voltage-gated Ca(2+) channels with high affinity and to modify the voltage-dependent gating of these channels. Here we describe the nuclear magnetic resonance (NMR) solution structure of kurtoxin determined using two- and three-dimensional NMR spectroscopy with dynamical simulated annealing calculations. The molecular structure of the toxin was highly similar to those of scorpion α-toxins and contained an α-helix, three β-strands, and several turns stabilized by four disulfide bonds. This so-called "cysteine-stabilized α-helix and β-sheet (CSαβ)" motif is found in a number of functionally varied small proteins. A detailed comparison of the backbone structure of kurtoxin with those of the scorpion α-toxins revealed that three regions [first long loop (Asp(8)-Ile(15)), β-hairpin loop (Gly(39)-Leu(42)), and C-terminal segment (Arg(57)-Ala(63))] in kurtoxin significantly differ from the corresponding regions in scorpion α-toxins, suggesting that these regions may be important for interacting with Cav3 (T-type) Ca(2+) channels. In addition, the surface profile of kurtoxin shows a larger and more focused electropositive patch along with a larger hydrophobic surface compared to those seen on scorpion α-toxins. These distinct surface properties of kurtoxin could explain its binding to Cav3 (T-type) voltage-gated Ca(2+) channels.

Structure and orientation of a voltage-sensor toxin in lipid membranes

Amphipathic protein toxins from tarantula venom inhibit voltage-activated potassium (Kv) channels by binding to a critical helix-turn-helix motif termed the voltage sensor paddle. Although these toxins partition into membranes to bind the paddle motif, their structure and orientation within the membrane are unknown. We investigated the interaction of a tarantula toxin named SGTx with membranes using both fluorescence and NMR spectroscopy. Depth-dependent fluorescence-quenching experiments with brominated lipids suggest that Trp30 in SGTx is positioned approximately 9 A from the center of the bilayer. NMR spectra reveal that the inhibitor cystine knot structure of the toxin does not radically change upon membrane partitioning. Transferred cross-saturation NMR experiments indicate that the toxin's hydrophobic protrusion contacts the hydrophobic core of the membrane, whereas most surrounding polar residues remain at interfacial regions of the bilayer. The inferred orientation of the toxin reveals a twofold symmetry in the arrangement of basic and hydrophobic residues, a feature that is conserved among tarantula toxins. These results have important implications for regions of the toxin involved in recognizing membranes and voltage-sensor paddles, and for the mechanisms by which tarantula toxins alter the activity of different types of ion channels.

Effects and mechanism of Chinese tarantula toxins on the Kv2.1 potassium channels

Three neurotoxins, Jingzhaotoxin-I, -III, and -V (JZTX-I, -III, and -V), isolated from the venom of the Chinese tarantula Chilobrachys Jingzhao, are 29-36-amino acid peptides. Electrophysiological recordings carried out in Xenopus laevis oocytes show that these toxins acted as gating modifier of voltage-dependent K+ channels. They slow the rate of Kv2.1 channel activation and increase the tail current deactivation, suggesting that toxin-bound channels can still open but are modified. JZTX-III selectively inhibits Kv2.1 channels, and JZTX-V exhibits a higher affinity to Kv4.2 channels than to Kv2.1 channels, whereas JZTX-I inhibits Kv2.1 and Kv4.1 channels with low affinity. Structure-function analysis indicates that electrostatic interactions can benefit for toxin affinity and the feature of electrostatic anisotropy may be correlated with the different affinity of the toxins for the Kv2.1 and Kv4.1 channels. Furthermore, phylogenetic analysis of these and other gating modifiers provides clues for the exploration of toxin-channel interaction.

Tarantula toxins interacting with voltage sensors in potassium channels

Voltage-activated ion channels open and close in response to changes in membrane voltage, a process that is crucial for electrical signaling in the nervous system. The venom from many poisonous creatures contains a diverse array of small protein toxins that bind to voltage-activated channels and modify the gating mechanism. Hanatoxin and a growing number of related tarantula toxins have been shown to inhibit activation of voltage-activated potassium (K(v)) channels by interacting with their voltage-sensing domains. This review summarizes our current understanding of the mechanism by which these toxins alter gating, the location of the toxin receptor within K(v) channels and the disposition of this receptor with respect to the lipid membrane. The conservation of tarantula toxin receptors among voltage-activated ion channels will also be discussed.

Classification of spider neurotoxins using structural motifs by primary structure features. Single residue distribution analysis and pattern analysis techniques

In recent years the data on the novel structures of spider toxins have been greatly increasing. The sequence data should be classified. We introduced two primary structure analysis techniques-single residue distribution analysis (SRDA) and pattern analysis for classifying spider polypeptide toxins with molecular weight less than 10kDa. For multiple sequence alignment, we also introduced three novel sequence representation formats named as a simple record, motif record and a pattern record, which can be useful for large-scale analysis of structures. About 300 sequences of spider toxins were analyzed and nine primary structure motifs were identified. New classification of spider toxins was proposed on the basis of previously described principal structural motif (PSM) and extra structural motif (ESM) [Kozlov, S.A., Malyavka, A.A., McCutchen, B., Lu, A., Schepers, E., Herrmann, R., Grishin, E.V., 2005. A novel strategy for the identification of toxin-like structures in spider venom. Proteins 59 (1), 131-140]. Five main structural classes were revealed, and for putative ion channel inhibitors from the most numerous classes 1, 2, and 3, five-digital personal ID numbers were introduced. A reference table with simple, motif and pattern representation sequence formats was created for all analyzed structures.

Effects of spider Macrothele raven venom on cell proliferation and cytotoxicity in HeLa cells

AIM

To examine the effect of venom from the spider Macrothele raven on cell proliferation and cytotoxicity in human cervical carcinoma, HeLa cells.

METHODS

Morphological and biochemical signs of apoptosis appeared using acridine orange-ethidium bromide (AO/EB) staining. Marked morphological changes in HeLa cells after treatment with spider venom were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cell proliferation and cytotoxicity were determined by [methyl-3H] thymidine assay ([3H]TdR) and lactate dehydrogenase (LDH) release, respectively. DNA fragmentation and cell cycle distribution were monitored using flow cytometry. In addition, Western blot analysis was used to evaluate the level of caspase-3 expression. In vivo examination of the inhibition of the size of tumors in nude mice treated with spider venom was measured.

RESULTS

Marked morphological changes were observed using AO/EB staining, SEM and TEM assay. Spider venom at concentrations of 10-40 mg/L caused dose- and time-dependent inhibition of HeLa cell proliferation. The ratio of apoptosis and necrosis increased. The activity of caspase-3 was upregulated after spider venom treatment. In vivo study of tumor size revealed that tumors significantly decreased in size from controls to tumors treated for 3 weeks with spider venom (P<0.05).

CONCLUSION

The inhibition of HeLa cells by the venom of the spider Macrothele raveni was carried out in three ways: induction of apoptosis, necrosis of toxicity damage and direct lysis. Spider venom is a novel anti-tumor material both in vitro and in vivo.

Molecular surface of tarantula toxins interacting with voltage sensors in K(v) channels

The venom from spiders, scorpions, and sea anemone contain a rich diversity of protein toxins that interact with ion channel voltage sensors. Although atomic structures have been solved for many of these toxins, the surfaces that are critical for interacting with voltage sensors are poorly defined. Hanatoxin and SGTx are tarantula toxins that inhibit activation of K(v) channels by interacting with each of the four voltage sensors. In this study we set out to identify the active surface of these toxins by alanine-scanning SGTx and characterizing the interaction of each mutant with the K(v)2.1 channel. Examination of the concentration dependence for inhibition identified 15 mutants with little effect on the concentration dependence for toxin inhibition of the K(v)2.1 channel, and 11 mutants that display moderate to dramatic perturbations. Mapping of these results onto the structure of SGTx identifies one face of the toxin where mutations with pronounced perturbations cluster together, and a backside of the toxin where mutations are well tolerated. The active surface of SGTx contains a ring-like assembly of highly polar residues, with two basic residues that are particularly critical, concentrically arranged around a hydrophobic protrusion containing critical aliphatic and aromatic residues. These results identify the active surface of the toxin and reveal the types of side chains that are important for interacting with voltage sensors.

Localization of the Voltage-Sensor Toxin Receptor on KvAP

A variety of venomous animals produce small protein toxins that impair the function of voltage-dependent cation channels by affecting the motions of the voltage-sensor domains and altering the energetics of the opening of the channel. In this study, we investigate the location of the receptor for tarantula venom voltage-sensor toxins on the voltage-dependent K+ channel from Aeropyrum pernix (KvAP), an archeabacterial channel that is functionally inhibited by members of this toxin family. We show that it is possible to purify the same set of toxins from venom of the tarantula Grammostola spatulata using either the purified KvAP voltage-sensor domain or the full-length KvAP channel. The equivalence of toxin retention profiles for the two channel proteins implies that the tarantula voltage-sensor toxin receptor resides exclusively on the voltage-sensor domain and that the pore is not required for the toxin-channel interaction. We have identified and characterized the functional properties of a subset of the tarantula toxins that bind to the KvAP voltage-sensor domain. Some of these toxins, VSTX1 and GSMTX4, have been previously isolated, while others, VSTX2 and VSTX3, are new members of the tarantula voltage-sensor toxin family. Some but not all toxins that bind to the voltage-sensor domain affect voltage-dependent gating of KvAP channels in lipid membranes.

Tarantulas: eight-legged pharmacists and combinatorial chemists

Tarantula venoms represent a cornucopia of novel ligands for a variety of cell receptors and ion channels. The diversity of peptide toxin pharmacology has been barely explored as indicated by pharmacological, toxicological and mass spectrometry investigations on more than 55 tarantula venoms. MALDI-TOF MS analysis reveals that the pharmacological diversity is based on relatively small size peptides, which seem to fall into a limited number of structural patterns. Properties and biological activities of the 33 known peptide toxins from tarantula venoms are described. Most known toxins conform to the Inhibitory Cystine Knot (ICK) motif, with differences in the length of intercysteine loops. Recently described peptides show that tarantula toxins can fold according to an elaboration of the Disulfide-Directed beta-Hairpin (DDH) motif which is also the canonical motif for the ICK fold. The ICK fold itself offers many variations leading to differing toxin properties. Examination of pharmacological data gives insights on the possible conserved site of action of toxins acting on voltage-gated ion channels and other toxins acting by a pore-blocking mechanism. Structure-activity data shows the versatility of the toxin scaffolds and the importance of surface features in the selectivity and specificity of these toxins. Tarantulas appear to be a good model for the discovery of novel compounds with important therapeutic potential, and for the study of the molecular evolution of peptide toxins.

Interaction between extracellular Hanatoxin and the resting conformation of the voltage-sensor paddle in Kv channels

In voltage-activated potassium (Kv) channels, basic residues in S4 enable the voltage-sensing domain to move in response to membrane depolarization and thereby trigger the activation gate to open. In the X-ray structure of the KvAP channel, the S4 helix is located near the intracellular boundary of the membrane where it forms a "voltage-sensor paddle" motif with the S3b helix. It has been proposed that the paddle is lipid-exposed and that it translocates through the membrane as it activates. We studied the interaction of externally applied Hanatoxin with the voltage-sensor paddle in Kv channels and show that the toxin binds tightly even at negative voltages where the paddle is resting and the channel is closed. Moreover, measurements of gating charge movement suggest that Hanatoxin interacts with and stabilizes the resting paddle. These findings point to an extracellular location for the resting conformation of the voltage-sensor paddle and constrain its transmembrane movements during activation.

Huwentoxin-V, a novel insecticidal peptide toxin from the spider Selenocosmia huwena, and a natural mutant of the toxin: indicates the key amino acid residues related to the biological activity

A neurotoxin peptide (named Huwentoxin-V) was purified from the venom of the Chinese bird spider Selenocosmia huwena by a combination of ion exchange chromatography and reverse phase HPLC. HWTX-V has 35 amino acid residues, and is in perfect agreement with the molecular mass 4111.4 Da identified by mass spectrometry. A natural mutant of the toxin (called mHuwentoxin-V) was also isolated from the venom. mHWTX-V was only truncated two amino acid residues from the C-terminus of HWTX-V, and its molecular weight is 3877.1 Da determined by mass spectrometry. The six cysteine residues in each sequence of the two peptides suggest three disulfide bridges, the present of which was demonstrated by mass spectrometry after dithiothreiotol reduce and S-carboxymethylation. The primary structure of the two toxins exhibits sequence identity with other spider toxins such as ProTx-I (64%), SGTx (57%), SNX-482 (55%), and Hanatoxin (54%). HWTX-V can reversibly paralyze locusts and cockroaches for several hours with a ED50 value as 16 +/- 5 microg/g to locusts, and a larger dose of the toxin can cause death. However, mHWTX-V shows no significant effect on locusts and cockroaches. The structure-activity relationship indicates that the residues Phe34 and Ser35 in the C-terminus of HWTX-V are the key residues of the biological activity.

Novel tarantula toxins for subtypes of voltage-dependent potassium channels in the Kv2 and Kv4 subfamilies

Three novel peptides with the ability to inhibit voltage-dependent potassium channels in the shab (Kv2) and shal (Kv4) subfamilies were identified from the venom of the African tarantulas Stromatopelma calceata (ScTx1) and Heteroscodra maculata (HmTx1, HmTx2). The three toxins are 34- to 38-amino acid peptides that belong to the structural family of inhibitor cystine knot spider peptides reticulated by three disulfide bridges. Electrophysiological recordings in COS cells show that these toxins act as gating modifier of voltage-dependent K+ channels. ScTx1 is the first high-affinity inhibitor of the Kv2.2 channel subtype (IC50, 21.4 nM) to be described. ScTx1 also inhibits the Kv2.1 channels, with an IC50 of 12.7 nM, and Kv2.1/Kv9.3 heteromultimers that have been proposed to be involved in O2 sensing in pulmonary artery myocytes. In addition, it is the most effective inhibitor of Kv4.2 channels described thus far, with an IC50 of 1.2 nM. HmTx toxins share sequence similarities with both the potassium channel blocker toxins (HmTx1) and the calcium channel blocker toxin omega-GsTx SIA (HmTx2). They inhibit potassium current associated with Kv2 subtypes in the 100 to 300 nM concentration range. HmTx2 seems to be a specific inhibitor of Kv2 channels, whereas HmTx1 also inhibits Kv4 channels, including Kv4.1, with the same potency. HmTx1 is the first described peptide effector of the Kv4.1 subtype. Those novel toxins are new tools for the investigation of the physiological role of the different potassium channel subunits in cellular physiology.

Pharmacology and biochemistry of spider venoms

Spider venoms represent an incredible source of biologically active substances which selectively target a variety of vital physiological functions in both insects and mammals. Many toxins isolated from spider venoms have been invaluable in helping to determine the role and diversity of neuronal ion channels and the process of exocytosis. In addition, there is enormous potential for the use of insect specific toxins from animal sources in agriculture. For these reasons, the past 15-20 years has seen a dramatic increase in studies on the venoms of many animals, particularly scorpions and spiders. This review covers the pharmacological and biochemical activities of spider venoms and the nature of the active components. In particular, it focuses on the wide variety of ion channel toxins, novel non-neurotoxic peptide toxins, enzymes and low molecular weight compounds that have been isolated. It also discusses the intraspecific sex differences in given species of spiders.

Conformational study of a new SGTx1 neurotoxin from the spider Scodra griseipes using mass spectrometry

SGTx1 is a new neurotoxin from the venom of Scodra griseipes. Because of the small quantity of this natural peptide available, mass spectrometry was used to obtain information on its higher-order structure. The kinetics of reduction by 1,4-dithiothreitol (DTT) was monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), and showed that one of the three disulfide bridges was appreciably more accessible to the DTT. Studies based on the charge state distribution (CSD) and H/D exchange of the non-reduced peptide, under neutral and acidic conditions, were performed using electrospray mass spectrometry (ES-MS). In neutral solution, SGTx1 showed a maximum charge state of four compared with seven potentially protonated basic residues, and all labile hydrogens were exchanged. However, under acidic conditions, a maximum charge state of only five was observed, and four of the labile hydrogens could not be deuterated. These observations are interpreted in terms of a rigid structure maintained by the disulfide bridges, which can be temporarily relaxed by disulfide bridge scrambling only at higher pH values.

Purification, structure determination and synthesis of covalitoxin-II, a short insect-specific neurotoxic peptide from the venom of the Coremiocnemis validus (Singapore tarantula)

Spider venoms contain toxins that specifically immobilize and kill insects. We report the purification and characterization of a new insect-specific toxin named covalitoxin-II (Cvtx-II; mass, 3406. 24+/-0.64), from Coremiocnemis validus (Singapore tarantula) venom. The complete 31 amino acid sequence of Cvtx-II has been determined and it shows less than 40% identity with spider toxins. However, Cvtx-II has conserved cystine motif analogous to other spider and omega-conotoxins. Cvtx-II was chemically synthesized and identified with the native Cvtx-II. Synthetic Cvtx-II induced insect-specific non-lethal excitatory activity when injected into crickets, but not in cockroaches and mice.