Two classes of channel-specific toxins from funnel web spider venom

1. The paralytic effects and neuromuscular actions of Agelenopsis aperta venom on insects were analyzed biochemically and electrophysiologically. 2. Paralysis caused by Agelenopsis venom is correlated with two effects on neuromuscular transmission: postsynaptic inhibition and presynaptic excitation. These effects are explained by the actions of two classes of toxins purified by RPLC, the alpha- and mu-agatoxins. 3. The alpha-agatoxins are low molecular weight, acylpolyamines which cause rapid, reversible paralysis correlated with use-dependent postsynaptic block of EPSPs and ionophoretic glutamate potentials. The mu-agatoxins are cysteine-rich polypeptides which cause irreversible paralysis and repetitive action potentials originating in presynaptic axons or nerve terminals. 4. The joint actions of the alpha- and mu-agatoxins lead to significantly higher rates of paralysis than are obtained by either toxin class alone, and this may relate to enhancement by excitatory mu-agatoxins of use-dependent block caused by alpha-agatoxins.     

Solution structure of Phrixotoxin 1, a specific peptide inhibitor of Kv4 potassium channels from the venom of the theraphosid spider Phrixotrichus auratus

Animal toxins block voltage-dependent potassium channels (Kv) either by occluding the conduction pore (pore blockers) or by modifying the channel gating properties (gating modifiers). Gating modifiers of Kv channels bind to four equivalent extracellular sites near the S3 and S4 segments, close to the voltage sensor. Phrixotoxins are gating modifiers that bind preferentially to the closed state of the channel and fold into the Inhibitory Cystine Knot structural motif. We have solved the solution structure of Phrixotoxin 1, a gating modifier of Kv4 potassium channels. Analysis of the molecular surface and the electrostatic anisotropy of Phrixotoxin 1 and of other toxins acting on voltage-dependent potassium channels allowed us to propose a toxin interacting surface that encompasses both the surface from which the dipole moment emerges and a neighboring hydrophobic surface rich in aromatic residues.     

omega-Aga-I: a presynaptic calcium channel antagonist from venom of the funnel web spider, Agelenopsis aperta

Spider venoms are proving to be important sources of specific ion channel toxins. Venom of Agelenopsis aperta, a funnel web spider, contains a class of polypeptide toxins which blocks neuromuscular synapses at nanomolar concentrations. Detailed physiological analyses of block caused by one of these toxins, omega-Aga-I, show that it suppresses transmitter release at insect and frog neuromuscular junctions and blocks calcium spikes in insect neuronal cell bodies. omega-Aga-I may define a binding site on neuronal calcium channels which is common to both vertebrates and invertebrates.     

Omega-agatoxins: novel calcium channel antagonists of two subtypes from funnel web spider (Agelenopsis aperta) venom

A new series of polypeptide presynaptic antagonists ("omega-agatoxins") was purified from venom of the funnel web spider Agelenopsis aperta. Physiological data indicate that all of these peptides are antagonists of voltage-sensitive calcium channels. Although all three omega-agatoxins (Aga) described here (omega-Aga-IA, omega-Aga-IB, and omega-Aga-IIA) block insect neuromuscular transmission presynaptically, biochemical data permit their subclassification as Type I and Type II toxins. Type I toxins (omega-Aga-IA and -IB) are 7.5 kDa, have closely related amino acid sequences, and exhibit characteristic tryptophan-like UV absorbance spectra. Complete Edman sequencing of omega-Aga-IA reveals it to be a 66-amino acid polypeptide containing 9 cysteines and 5 tryptophan residues. omega-Aga-IIA, a Type II toxin, is 11 kDa, shows limited amino acid sequence similarity to the Type I toxins, and exhibits mixed tryptophan- and tyrosine-like absorbance. Nanomolar concentrations of omega-Aga-IIA inhibit the specific binding of 125I-labeled omega-conotoxin GVIA to chick synaptosomal membranes while omega-Aga-IA and -IB have no effect under identical conditions. The omega-agatoxins thus are defined as two subtypes of neuronal calcium channel toxins with different structural characteristics and calcium channel binding specificities.     

An endogenous antitoxin to the lethal venom of the funnel web spider, Atrax robustus, in rabbit sera.

1. An endogenous antitoxin fraction was isolated from non-immune rabbit sera by affinity chromatography with robustoxin bound to the solid support. 2. Robustoxin is the sole lethal toxin in the venom of the male funnel web spider, Atrax robustus. 3. The fraction was found to contain IgG and IgM immunoglobulins. 4. This fraction prevented or reversed the lethal actions of the crude venom in newborn mice, in mouse phrenic nerve-hemidiaphragm preparations, and in anaesthetized monkeys. 5. The antitoxin fraction is of potential value in the therapy of human envenomation by A. robustus.     

Voltage-gated sodium channels are targets for toxins from the venom of the spider Heriaeus melloteei

Three novel peptides were isolated from the venom of the spider Heriaeus melloteei (Thomisidae) and characterized. The peptides named Hm-1, 2 and 3 blocked voltage-gated Na⁺ channels at concentrations in the order of 100 nM. Activity of the purified peptides was investigated in Na⁺ channel isoforms of mammals and insects. Hm-1 and 2 appeared to act as pore blockers, whereas Hm-3 modulated the channel activation process. The toxins described exhibit minor similarity with other known peptides and may therefore constitute new groups of Na⁺ channel ligands.     

Identification of a peptide toxin from Grammostola spatulata spider venom that blocks cation-selective stretch-activated channels

We have identified a 35 amino acid peptide toxin of the inhibitor cysteine knot family that blocks cationic stretch-activated ion channels. The toxin, denoted GsMTx-4, was isolated from the venom of the spider Grammostola spatulata and has <50% homology to other neuroactive peptides. It was isolated by fractionating whole venom using reverse phase HPLC, and then assaying fractions on stretch-activated channels (SACs) in outside-out patches from adult rat astrocytes. Although the channel gating kinetics were different between cell-attached and outside-out patches, the properties associated with the channel pore, such as selectivity for alkali cations, conductance ( approximately 45 pS at -100 mV) and a mild rectification were unaffected by outside-out formation. GsMTx-4 produced a complete block of SACs in outside-out patches and appeared specific since it had no effect on whole-cell voltage-sensitive currents. The equilibrium dissociation constant of approximately 630 nM was calculated from the ratio of association and dissociation rate constants. In hypotonically swollen astrocytes, GsMTx-4 produces approximately 40% reduction in swelling-activated whole-cell current. Similarly, in isolated ventricular cells from a rabbit dilated cardiomyopathy model, GsMTx-4 produced a near complete block of the volume-sensitive cation-selective current, but did not affect the anion current. In the myopathic heart cells, where the swell-induced current is tonically active, GsMTx-4 also reduced the cell size. This is the first report of a peptide toxin that specifically blocks stretch-activated currents. The toxin affect on swelling-activated whole-cell currents implicates SACs in volume regulation.     

间斑寇蛛粗毒的生物学特性

近几十年来,间斑寇蛛(Latrodectus tredecimguttatus)已引起相关研究工作者的广泛关注,因为阐明其毒液中的特异性蛋白质和多肽活性成分对蜘蛛咬伤治疗具有重要的意义,且其粗毒液中的生物学活性成分在神经生物学和药物研究方面也有着潜在的应用前景。但直到现在,尽管已有不少研究报道了包括α-latrotoxin在内的几种间斑寇蛛毒性蛋白质的生物学性质和结构,但有关毒液生物学特性的系统研究的报道还很少。本研究采用解剖分离毒囊的方法从产于我国新疆的间斑寇蛛提取粗毒,并对其理化和生物学性质进行了系统的分析。定量测定结果表明,粗毒的蛋白质含量为36.99%,对小鼠和蜚蠊的LD50分别为0.39mg/kg和2.32μg/g体重。小鼠经腹腔注射粗毒后,出现呆滞、共济失调、排汗、痉挛、食欲减退、呼吸短促、睁眼困难等中毒症状,而注射生理盐水的对照小鼠活动正常。粗毒具有透明质酸酶、碱性磷酸酶、酸性磷酸酶、脱氧核糖核酸酶、乙酰胆碱酯酶、蛋白水解酶等多种水解酶的活性。10μg/ml该粗毒可以在31min±3.05min内完全抑制电刺激引起的大鼠输精管的收缩反应。6μg/ml粗毒可在25min±2.2min内完全阻断小鼠膈神经-膈肌标本的神经肌肉接头传递。膜片钳电生理实验显示,粗毒(1g/L)对蜚蠊背侧不成对中间(Dorsal unpaired median,DUM)神经元的快瞬时钾电流、钠电流、高电压激活的钙电流和大鼠背根神经节(Dorsal root ganglion,DRG)细胞延迟整流钾电流、TTX-S型钠电流、高电压激活的钙电流均无明显作用。     

ω-Aga-I: A presynaptic calcium channel antagonist from venom of the funnel web spider,Agelenopsis aperta

Spider venoms are proving to be important sources of specific ion channel toxins. Venom of Agelenopsis aperta, a funnel web spider, contains a class of polypeptide toxins which blocks neuromuscular synapses at nanomolar concentrations. Detailed physiological analyses of block caused by one of these toxins, ω-Aga-I show that it suppresses transmitter release at insect and frog neuromuscular junctions and blocks calcium spikes in insect neuronal cell bodies. ω-Aga-I may define a binding site on neuronal calcium channels which is common to both vertebrates and invertebrates.     

An insecticidal peptide from the theraposid Brachypelma smithi spider venom reveals common molecular features among spider species from different genera

The soluble venom of the Mexican theraposid spider Brachypelma smithi was screened for insecticidal peptides based on toxicity to house crickets. An insecticidal peptide, named Bs1 (which stands for Brachypelma smithi toxin 1) was obtained in homogeneous form after the soluble venom was fractionated using reverse-phase and cation-exchange chromatography. It contains 41 amino acids cross-linked by three disulfide bridges. Its sequence is similar to an insecticidal peptide isolated from the theraposid spider Ornithoctonus huwena from China, and another from the hexathelid spider Macrothelegigas from Japan, indicating that they are phylogenetically related. A cDNA library was prepared from the venomous glands of B. smithi and the gene that code for Bs1 was cloned. Sequence analysis of the nucleotides of Bs1 showed similarities to that of the hexathelid spider from Japan proving additional evidence for close genetic relationship between these spider peptides. The mRNAs of these toxins code for signal peptides that are processed at the segment rich in acidic and basic residues. Their C-terminal amino acids are amidated. However, they contain only a glycine residue at the most C-terminal position, without the presence of additional basic amino acid residues, normally required for post-translation processing of other toxins reported in the literature. The possible mechanism of action of Bs1 was investigated using several ion channels as putative receptors. Bs1 had minor, but significant effects on the Para/tipE insect ion channel, which could indirectly correlate with the observed lethal activity to crickets.     

ArgTX-636, a polyamine isolated from spider venom: A novel class of melanogenesis inhibitors

To discover new molecules with an inhibitory activity of melanogenesis a hundred of scorpions, snakes, spiders and amphibians venoms were screened for their capacity to inhibit mushroom tyrosinase using 3,4-l-dihydroxyphenylalanine (l-DOPA) as substrate.The Argiope lobata spider venom proved to be the most active. HPLC fraction containing Argiotoxine-636 (ArgTX-636), a polyamine known for its numerous biological activities, was found to also show a good regulation activity of melanogenesis by inhibiting DOPA and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) oxidases activities, wore by tyrosinase (TYR) and tyrosinase-related protein 1 (TRP-1), respectively. Our results demonstrate that ArgTX-636 reduced the mushroom tyrosinase activity in a dose-dependent way with a maximal half inhibitory concentration (IC₅₀) value of 8.34 μM, when l-DOPA is used as substrate. The Lineweaver–Burk study showed that ArgTX-636 is a mixed type inhibitor of the diphenolase activity. Moreover, ArgTX-636 inhibits DHICA oxydase activity of mushroom tyrosinase activity with IC₅₀ at 41.3 μM. ArgTX-636 has no cytotoxicity in B16F10 melanoma cells at concentrations up to 42.1 μM. The effect of ArgTX-636 on melanogenesis showed that melanin production in B16F10 melanoma cell decreased by approximatively 70% compared to untreated cells. ArgTX-636 displayed no significant effect on the TYR expression while the protein level of TRP-1 decreased in B16F10 cells. Thus, ArgTX-636 could have particular interest for cosmetic and/or pharmaceutical use in order to reduce important dermatoses in black and mixed skins.     

Effect of Segestria florentina spider venom on the mechanism of inactivation of sodium channels

It was shown that Segestria florentina spider venom mainly reduces the rate and amount of sodium inactivation. This effect is likely to be responsible for the prolongation of the action potential.     

Tunable calcium current through TRPV1 receptor channels

TRPV1 receptors are polymodal cation channels that open in response to diverse stimuli including noxious heat, capsaicin, and protons. Because Ca2+ is vital for TRPV1 signaling, we sought to precisely measure its contribution to TRPV1 responses and discovered that the Ca2+ current was tuned by the mode of activation. Using patch clamp photometry, we found that the fraction of the total current carried by Ca2+ (called the Pf%) was significantly smaller for TRPV1 currents evoked by protons than for those evoked by capsaicin. Using site-directed mutagenesis, we discovered that the smaller Pf% was due to protonation of three acidic amino acids (Asp646, Glu648, and Glu651) that are located in the mouth of the pore. Thus, in keeping with recent reports of time-dependent changes in the ionic permeability of some ligand-gated ion channels, we now show for the first time that the physiologically important Ca2+ current of the TRPV1 receptor is also dynamic and depends on the mode of activation. This current is significantly smaller when the receptor is activated by a change in pH, owing to atomic scale interactions of H+ and Ca2+ with the fixed negative charge of side chains in the pore.     

Molecular diversity of spider venom

Spider venom, a factor that has played a decisive role in the evolution of one of the most successful groups of living organisms, is reviewed. Unique molecular diversity of venom components including substances of variable structure (from simple low molecular weight compounds to large multidomain proteins) with different functions is considered. Special attention is given to the structure, properties, and biosynthesis of toxins of polypeptide nature.     

Electrophysiological properties of heteromeric TRPV4-C1 channels

We previously reported that TRPV4 and TRPC1 can co-assemble to form heteromeric TRPV4-C1 channels [12]. In the present study, we characterized some basic electrophysiological properties of heteromeric TRPV4-C1 channels. 4α-Phorbol 12,13-didecanoate (4α-PDD, a TRPV4 agonist) activated a single channel current in HEK293 cells co-expressing TRPV4 and TRPC1. The activity of the channels was abrogated by a TRPC1-targeting blocking antibody T1E3. Conductance of the channels was ~95pS for outward currents and ~83pS for inward currents. The channels with similar conductance were also recorded in cells expressing TRPV4-C1 concatamers, in which assembled channels were expected to be mostly 2V4:2C1. Fluorescence Resonance Energy Transfer (FRET) experiments confirmed the formation of a protein complex with 2V4:2C1 stoichiometry while suggesting an unlikeliness of 3V4:1C1 or 1V4:3C1 stoichiometry. Monovalent cation permeability profiles were compared between heteromeric TRPV4-C1 and homomeric TRPV4 channels. For heteromeric TRPV4-C1 channels, their permeation profile was found to fit to Eisenman sequence VI, indicative of a strong field strength cation binding site, whereas for homomeric TRPV4 channels, their permeation profile corresponded to Eisenman sequence IV for a weak field strength binding site. Compared to homomeric TRPV4 channels, heteromeric TRPV4-C1 channels were slightly more permeable to Ca2+ and had a reduced sensitivity to extracellular Ca2+ inhibition. In summary, we found that, when TRPV4 and TRPC1 were co-expressed in HEK293 cells, the predominate assembly type was 2V4:2C1. The heteromeric TRPV4-C1 channels display distinct electrophysiological properties different from those of homomeric TRPV4 channels.     

Bisandrographolide from Andrographis paniculata activates TRPV4 channels

Many transient receptor potential (TRP) channels are activated or blocked by various compounds found in plants; two prominent examples include the activation of TRPV1 channels by capsaicin and the activation of TRPM8 channels by menthol. We sought to identify additional plant compounds that are active on other types of TRP channels. We screened a library of extracts from 50 Chinese herbal plants using a calcium-imaging assay to find compounds active on TRPV3 and TRPV4 channels. An extract from the plant Andrographis paniculata potently activated TRPV4 channels. The extract was fractionated further, and the active compound was identified as bisandrographolide A (BAA). We used purified compound to characterize the activity of BAA on certain TRPV channel subtypes. Although BAA activated TRPV4 channels with an EC(50) of 790-950 nm, it did not activate or block activation of TRPV1, TRPV2, or TRPV3 channels. BAA activated a large TRPV4-like current in immortalized mouse keratinocytes (308 cells) that have been shown to express TRPV4 protein endogenously. This compound also activated TRPV4 currents in cell-free outside-out patches from HEK293T cells overexpressing TRPV4 cDNA, suggesting that BAA can activate the channel in a membrane-delimited manner. Another related compound, andrographolide, found in abundance in the plant Andrographis was unable to activate or block activation of TRPV4 channels. These experiments show that BAA activates TRPV4 channels, and we discuss the possibility that activation of TRPV4 by BAA could play a role in some of the effects of Andrographis extract described in traditional medicine.     

An experimental study of the effects of spider venom on animals

The effects of venom of spiders from the families Pisauridae, Argyronetidae, and Araneidae on different animals (worms, mollusks, arthropods, fishes, and mammals) were studied. The animals of different classes varied in their sensitivity to spider venom. The animals that can be a potential prey were the most sensitive. The venom of spider females was more efficient than that of males. The spiders were found to be able to kill five victims in sequence; the most effective action of venom was on the first two ones. The venom regenerates in 1.5–2.0 hours.     

Glutamate receptor antagonists from the spider Argiope lobata venom

Homologous low molecular weight compounds blocking postsynaptic glutamate receptors were isolated from the Argiope lobata spider venom by ion-exchange chromatography and reverse-phase HPLC. Structures of nine different blocking agents were determined by NMR and mass spectroscopy. They can be divided into three groups: argiopin, argiopinins and pseudoargiopinines. The major principles of the structural organization of the novel class of antagonists of glutamate receptors were considered.     

Genes and evolution of two-domain toxins from lynx spider venom

Spiderines are comparatively long polypeptide toxins (∼110 residues) from lynx spiders (genus Oxyopes). They are built of an N-terminal linear cationic domain (∼40 residues) and a C-terminal knottin domain (∼60 residues). The linear domain empowers spiderines with strong cytolytic activity. In the present work we report 16 novel spiderine sequences from Oxyopes takobius and Oxyopes lineatus classified into two subfamilies. Strikingly, negative selection acts on both linear and knottin domains. Genes encoding Oxyopes two-domain toxins were sequenced and found to be intronless. We further discuss a possible scenario of lynx spider modular toxin evolution.