Structures of paralytic acylpolyamines from the spider Agelenopsis aperta

Kainate Receptor Antagonists: Recent Advances and Therapeutic Perspective

Since the 1990s, ionotropic glutamate receptors have served as an outstanding target for drug discovery research aimed at the discovery of new neurotherapeutic agents. With the recent approval of perampanel, the first marketed non-competitive antagonist of AMPA receptors, particular interest has been directed toward 'non-NMDA' (AMPA and kainate) receptor inhibitors. Although the role of AMPA receptors in the development of neurological or psychiatric disorders has been well recognized and characterized, progress in understanding the function of kainate receptors (KARs) has been hampered, mainly due to the lack of specific and selective pharmacological tools. The latest findings in the biology of KA receptors indicate that they are involved in neurophysiological activity and play an important role in both health and disease, including conditions such as anxiety, schizophrenia, epilepsy, neuropathic pain, and migraine. Therefore, we reviewed recent advances in the field of competitive and non-competitive kainate receptor antagonists and their potential therapeutic applications. Due to the high level of structural divergence among the compounds described here, we decided to divide them into seven groups according to their overall structure, presenting a total of 72 active compounds.

Antimicrobial activity and partial chemical structure of acylpolyamines isolated from the venom of the spider Acanthoscurria natalensis

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Synthesis and Biological Activities of Naturally Functionalized Polyamines: An Overview

Recently, extensive researches have emphasized the fact that polyamine conjugates are becoming important in all biological and medicinal fields. In this review, we will focus our attention on natural polyamines and highlight recent progress in both fundamental mechanism studies and interests in the development and application for the therapeutic use of polyamine derivatives.

Transcriptomic Analysis of Pseudoscorpion Venom Reveals a Unique Cocktail Dominated by Enzymes and Protease Inhibitors

Transcriptomic and genomic analyses have illuminated the diversity of venoms in three of the four venomous arachnid orders (scorpions, spiders, and ticks). To date, no venom gland transcriptome analysis has been available for pseudoscorpions, the fourth venomous arachnid lineage. To redress this gap, we sequenced an mRNA library generated from the venom glands of the species Synsphyronus apimelus (Garypidae). High-throughput sequencing by the Illumina protocol, followed by de novo assembly, resulted in a total of 238,331 transcripts. From those, we annotated 131 transcripts, which code for putative peptides/proteins with similar sequences to previously reported venom components available from different arachnid species in protein databases. Transcripts putatively coding for enzymes showed the richest diversity, followed by other venom components such as peptidase inhibitors, cysteine-rich peptides, and thyroglobulin 1-like peptides. Only 11 transcripts were found that code for putatively low molecular mass spider toxins. This study constitutes the first report of the diversity of components within pseudoscorpion venom.

The Aromatic Head Group of Spider Toxin Polyamines Influences Toxicity to Cancer Cells

Spider venoms constitute incredibly diverse libraries of compounds, many of which are involved in prey capture and defence. Polyamines are often prevalent in the venom and target ionotropic glutamate receptors. Here we show that a novel spider polyamine, PA₃₆₆, containing a hydroxyphenyl-based structure is present in the venom of several species of tarantula, and has selective toxicity against MCF-7 breast cancer cells. By contrast, a polyamine from an Australian funnel-web spider venom, which contains an identical polyamine tail to PA₃₆₆ but an indole-based head-group, is only cytotoxic at high concentrations. Our results suggest that the ring structure plays a role in the cytotoxicity and that modification to the polyamine head group might lead to more potent and selective compounds with potential as novel cancer treatments.

A template approach for the characterization of linear polyamines and derivatives in spider venom

A combination of high-performance liquid chromatography (HPLC) and atmospheric-pressure chemical ionization mass spectrometry (APCI-MS and APCI-MS/MS) was used to detect and characterize linear polyamine derivatives in the venom of the spiders Agelenopsis aperta, Hololena curta and Paracoelotes birulai. The compounds were identified with a template approach, by which the collision-induced dissociation (CID) spectra of known compounds are directly compared and correlated with those of the analytes. To facilitate the perception of the spectra and the recognition of the structural features of the analytes, an ion nomenclature closely leaned on the accepted nomenclature for fragment ions of peptides or nucleic acids is introduced. The structure identification of polyamine derivatives by direct correlation of MS spectra is possible because such compounds show very distinctive fragmentation behavior. Of particular relevance is the fact that the signal patterns that are observed with analytes possessing different polyamine backbones are not only distinct with regard to mass distributions but also with regard to relative signal intensities, resulting in fingerprint-like signal patterns. The direct correlation of these patterns--more than the correlation of the ion distributions--was found to be of key significance. With this, the new approach is fundamentally different from the sequencing of peptides or nucleic acids, which are largely based on mass distributions. The method is more efficient and more reliable than the de novo interpretation of the MS data and it even allows the identification of polyamine portions in compounds that are analyzed within mixtures.

Small molecules from spiders used as chemical probes

Spiders are important species in ecological systems and as major predators of insects they are endowed with a plethora of low-molecular-weight natural products having intriguing biological activities. The isolation and biological characterization of these entities are well established, however, only very recently have these compounds been used as templates for the design, synthesis, and biological evaluation of synthetic analogues. In contrast, the investigation of compounds responsible for chemical communication between spiders is far less developed, but recently new light has been shed onto the area of pheromones and allomones from spiders. Herein, we recapitulate these recent results, put them into perspective with previous findings, and provide an outlook for future studies of these chemotypes.

Painful toxins acting at TRPV1

Many plant and animal toxins cause aversive behaviors in animals due to their pungent or unpleasant taste or because they cause other unpleasant senstations like pain. This article reviews the current state of knowledge of toxins that act at the TRPV1 ion channel, which is expressed in primary sensory neurons, is activated by multiple painful stimuli and is thought to be a key pain sensor and integrator. The recent finding that painful peptide "vanillotoxin" components of tarantula toxin activate the TRPV1 ion channel to cause pain led us to survey what is known about toxins that act at this receptor. Toxins from plants, spiders and jellyfish are considered. Where possible, structural information about sites of interaction is considered in relation to toxin-binding sites on the Kv ion channel, for which more structural information exists. We discuss a developing model where toxin agonists such as resiniferatoxin and vanillotoxins are proposed to interact with a region of TRPV1 that is homologous to the "voltage sensor" in the Kv1.2 ion channel, to open the channel and activate primary sensory nerves, causing pain.

Peptides of arachnid venoms with insecticidal activity targeting sodium channels

Arachnids have a venom apparatus and secrete a complex chemical mixture of low molecular mass organic molecules, enzymes and polypeptide neurotoxins designed to paralyze or kill their prey. Most of these toxins are specific for membrane voltage-gated sodium channels, although some may also target calcium or potassium channels and other membrane receptors. Scorpions and spiders have provided the greatest number of the neurotoxins studied so far, for which, a good number of primary and 3D structures have been obtained. Structural features, comprising a folding that determines a similar spatial distribution of charged and hydrophobic side chains of specific amino acids, are strikingly common among the toxins from spider and scorpion venoms. Such similarities are, in turn, the key feature to target and bind these proteins to ionic channels. The search for new insecticidal compounds, as well as the study of their modes of action, constitutes a current approach to rationally design novel insecticides. This goal tends to be more relevant if the resistance to the conventional chemical products is considered. A promising alternative seems to be the biotechnological approach using toxin-expressing recombinant baculovirus. Spider and scorpion toxins having insecticidal activity are reviewed here considering their structures, toxicities and action mechanisms in sodium channels of excitable membranes.

Structural and biological characterization of one antibacterial acylpolyamine isolated from the hemocytes of the spider Acanthocurria gomesiana

We have isolated a 417Da antibacterial molecule, named mygalin, from the hemocytes of the spider Acanthoscurria gomesiana. The structure of mygalin was elucidated by tandem mass spectrometry (MS/MS) and by two spectroscopic techniques, nuclear magnetic resonance (NMR) and ultraviolet (UV) spectroscopy. Mygalin was identified as bis-acylpolyamine N1,N8-bis(2,5-dihydroxybenzoyl)spermidine, in which the primary amino groups of the spermidine are acylated with the carboxyl group of the 2,5-dihydroxybenzoic acid. Mygalin was active against Escherichia coli at 85muM, being this activity inhibited completely by catalase. Therefore, the antibacterial activity of mygalin was attributed to its production of hydrogen peroxide (H(2)O(2)). The putative mechanisms of formation of H(2)O(2) from mygalin are discussed. To our knowledge this is the first report of one bis-acylpolyamine with antibacterial activity purified from animal source.

An Inhibitor of TRPV1 Channels Isolated from Funnel Web Spider Venom†

Capsaicin receptor channels (TRPV1) are nonselective cation channels that integrate multiple noxious stimuli in sensory neurons. In an effort to identify new inhibitors of these channels we screened a venom library for activity against TRPV1 channels and found robust inhibitory activity in venom from Agelenopsis aperta, a north American funnel web spider. Fractionation of the venom using reversed-phase HPLC resulted in the purification of two acylpolyamine toxins, AG489 and AG505, which inhibit TRPV1 channels from the extracellular side of the membrane. The activity of AG489 was characterized further, and the toxin was found to inhibit TRPV1 channels with a K(i) of 0.3 microM at -40 mV. Inhibition of TRPV1 channels by AG489 is strongly voltage-dependent, with relief of inhibition at positive voltages, consistent with the toxin inhibiting the channel through a pore-blocking mechanism. We used scanning mutagenesis throughout the TM5-TM6 linker, a region thought to form the outer pore of TRPV1 channels, to identify pore mutations that alter toxin affinity. Four mutants dramatically decrease toxin affinity and several mutants increase toxin affinity, consistent with the notion that the TM5-TM6 linker forms the outer vestibule of TRPV1 channels and that AG489 is a pore blocker.

Agatoxins: ion channel specific toxins from the american funnel web spider, Agelenopsis aperta

Agatoxins from Agelenopsis aperta venom target three classes of ion channels, including transmitter-activated cation channels, voltage-activated sodium channels, and voltage-activated calcium channels. The alpha-agatoxins are non-competitive, use-dependent antagonists of glutamate receptor channels, and produce rapid but reversible paralysis in insect prey. Their actions are facilitated by the micro-agatoxins, which shift voltage-dependent activation of neuronal sodium channels to more negative potentials, causing spontaneous transmitter release and repetitive action potentials. The omega-agatoxins target neuronal calcium channels, modifying their properties in distinct ways, either through gating modification (omega-Aga-IVA) or by reduction of unitary current (omega-Aga-IIIA). The alpha-agatoxins and omega-agatoxins modify both insect and vertebrate ion channels, while the micro-agatoxins are selective for insect channels. Agatoxins have been used as selective pharmacological probes for characterization of ion channels in the brain and heart, and have been evaluated as candidate biopesticides.

Structures of spider toxins: hydroxyindole-3-acetylpolyamines and a new generalized structure of type-E compounds obtained from the venom of the Joro spider, Nephila clavata

Facile structure determination of acylpolyamines, glutamatergic nerve blocker obtained from the venom of the Joro spider (Nephila clavata) was carried out with the use of micro-column LC/MS and high energy collision induced dissociation (CID) mass spectrometry. 6-hydroxyindole-3-acetyl was proposed previously as a putative partial structure, for the acyl moiety of hydroxyindole-type polyamines (NPTX-1 to -6). The NMR data obtained for NPTX-6, NPTX-687 and hydroxyindole-3-acetic acid which was released by acid hydrolysis of Nephila clavata crude venom extracts proved that the lipophilic head is the 4-hydroxyindole-3-acetic acid. Various hydroxyindole-3-acetyl polyamines were found in N. Clavata venom and characterized by mass spectrometry. As a result, type-E, a new class of generalized acylpolyamine structure was proposed in addition to the previously reported polyamine backbones type-A to -D.

Labeling studies of photolabile philanthotoxins with nicotinic acetylcholine receptors: mode of interaction between toxin and receptor

BACKGROUND

The nicotinic acetylcholine receptors (nAChRs) and glutamate receptors are ligand-gated cation channels composed of five separate polypeptide chains. A 43 kDa protein of unknown function is noncovalently associated with the cytoplasmic side of nAChR in vivo. The venoms of many wasps and spiders contain toxins that block the activity of these channels. Philanthotoxin-433 (PhTX-433) is a non-competitive channel blocker found in the venom of the wasp Philanthus. We have used a photolabile derivative to investigate how PhTX-433 interacts with nAChRs.

RESULTS

A radiolabeled PhTX analog, containing a photolabile group substituted on one of its aromatic rings, photocrosslinked to all five subunits (alpha, alpha 1, beta, gamma, delta) of purified nAChR in the absence of the 43 kDa protein. In the presence of the 43 kDa protein, the alpha subunit was preferentially labeled. Proteolysis of the receptor after crosslinking indicated that the hydrophobic end (head) of the PhTx-433 analog bound to the cytoplasmic loop(s) of the alpha-subunit. Binding is inhibited by other non-competitive channel blockers such as the related polyamine-amide toxins from spiders and chlorpromazine.

CONCLUSIONS

These results, coupled with previous structure/activity studies, lead to a putative model of the binding of PhTx and related polyamine toxins to nAChRs in vitro. The 43 kDa protein appears to influence the orientation of toxin binding. Further binding studies are necessary to confirm the model and to define how toxins enter the receptor and how they are oriented within it. A precise understanding of ligand/receptor interaction is crucial for the design of drugs specific for a particular subtype of receptor.

Identification of bis(agmatine)oxalamide in venom from the primitive hunting spider, Plectreurys tristis (Simon)

N, N'-bis(4-guanidinobutyl)oxalamide, a novel bis(agmatine)oxalamide, is identified as a major component (8 micrograms/microliters) and the predominant acylpolyamine in venom from the primitive hunting spider, Plectreurys tristis. The function of this compound is unknown since it does not confer insecticidal or fungicidal activity in the systems examined.

Agelenopsis aperta venom and FTX, a purified toxin, inhibit acetylcholine release in Torpedo synaptosomes

The presence of P-type calcium channels in synaptosomes prepared from electric organ of Torpedo marmorata was investigated by using the venom of Agelenopsis aperta, a toxin purified from it, FTX, and its synthetic analog. We analysed the action of these agents on acetylcholine release which was continuously followed using a chemiluminescent assay. Agelenopsis aperta venom, FTX and synthetic FTX inhibit acetylcholine release from synaptosomes induced by a presynaptic membrane depolarization with 60 mM KCl. A stronger inhibition of acetylcholine release was observed with the venom than with FTX (70 and 50%, respectively). Another way of triggering acetylcholine release from Torpedo synaptosomes is to insert in the presynaptic membrane a calcium ionophore A23187 which allows the bypass of the natural calcium channels. The venom of Agelenopsis aperta inhibits A23187-evoked acetylcholine release. Purified and synthetic FTX does not possess this property, suggesting that this inhibition of acetylcholine release was due to other toxins of the venom. Another type of pharmacological sensitivity of Torpedo calcium channels was also demonstrated using omega-conotoxin GVIA. At a concentration of 20 microM, this toxin was able to inhibit about 35% of KCl-evoked acetylcholine release. When FTX + omega-conotoxin GVIA were applied together, the inhibitory effect on KCl-evoked acetylcholine release was not significantly increased in comparison with the one observed with FTX alone. In conclusion, we examined the effect of different agents on acetylcholine release from Torpedo marmorata electric organ synaptosomes; acetylcholine release was elicited with KCl depolarization and followed continuously with a chemiluminescent assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of polyamines with neuronal ion channels

Polyamines, a group of aliphatic amines, exert selective and complex actions on a variety of ion channels. Polyamines are found endogenously, as normal metabolic intermediates, and also in the venoms of several invertebrates, where they act as potent neurotoxins. In addition, evidence suggests that polyamines may mediate or potentiate excitotoxic mechanisms responsible for neuronal damage during ischaemia. Now that the structures and functions of various polyamines are beginning to be deduced, and synthetic analogues become available, these compounds are of importance, not only as pharmacological tools to study specific receptor/ion channel complexes, but also as templates on which to base drugs designed for neuroprotective effects in a number of neurodegenerative disorders.

Actions of arginine polyamine on voltage and ligand-activated whole cell currents recorded from cultured neurones

1. Toxins from invertebrates have proved useful tools for investigation of the properties of ion channels. In this study we describe the actions of arginine polyamine which is believed to be a close analogue of FTX, a polyamine isolated from the American funnel web spider, Agelenopsis aperta. 2. Voltage-activated Ca2+ currents and Ca(2+)-dependent Cl- currents recorded from rat cultured dorsal root ganglion neurones were reversibly inhibited by arginine polyamine (AP; 0.001 to 100 microM). Low voltage-activated T-type Ca2+ currents were significantly more sensitive to AP than high voltage-activated Ca2+ currents. The IC50 values for the actions of AP on low and high voltage-activated Ca2+ currents were 10 nM and 3 microM respectively. AP was equally effective in inhibiting high voltage-activated currents carried by Ba2+, Sr2+ or Ca2+. However, AP-induced inhibition of Ca2+ currents was attenuated by increasing the extracellular Ca2+ concentration from 2 mM to 10 mM. 3. The actions of AP on a Ca(2+)-independent K+ current were more complex, 1 microM AP enhanced this current but 10 microM AP had a dual action, initially enhancing but then inhibiting the K+ current. 4. gamma-Aminobutyric acid-activated Cl- currents were also reversibly inhibited by 1 to 10 microM AP. In contrast N-methyl-D-aspartate currents recorded from rat cultured cerebellar neurones were greatly enhanced by 10 microM AP. 5. We conclude that at a concentration of 10 nM, AP is a selective inhibitor of low threshold T-type voltage-activated Ca2+ currents. However, at higher concentrations 1-10 microM AP interacts with ion channels or other membrane constituents to produce a variety of actions on both voltage and ligand gated ion channels.

Arthropod toxins as leads for novel insecticides: an assessment of polyamine amides as glutamate antagonists

In the search for new toxins, preferably with new sites of action, the polyamine amides represent a new class of compounds with potential as insecticides and as pharmaceutical agents due to their antagonism of ligand-gated cation channels. In particular, they are potent antagonists of the L-glutamate receptors of insect skeletal muscle. In this paper, we report on synthetic studies to produce hybrid analogues based upon the argiotoxin spider toxins and philanthotoxin-433 which is obtained from a solitary, parasitic wasp. We speculate upon possible modes and sites of action for these antagonists and we discuss their potential as insecticides and in the possible treatment of ischaemic damage. The synthesis and characterization of 4-hydroxyphenylpropanoylspermine is reported and the locust muscle biological assay is described. Using this pharmacological screen, structure-activity relationships have been determined in our laboratories. These are reviewed in the light of the current literature. Voltage clamp studies of the synthetic analogue philanthotoxin-343 and the effects of this polyamine amide on glutamate receptors expressed in Xenopus oocytes are outlined. In conclusion, a description of our current ideas and understanding of the many sites and modes of action of the polyamine amides, based both upon our own studies and also upon those recently reported, is presented.

P-type calcium channels blocked by the spider toxin omega-Aga-IVA

Voltage-dependent calcium channels mediate calcium entry into neurons, which is crucial for many processes in the brain including synaptic transmission, dendritic spiking, gene expression and cell death. Many types of calcium channels exist in mammalian brains, but high-affinity blockers are available for only two types, L-type channels (targeted by nimodipine and other dihydropyridine channel blockers) and N-type channels (targeted by omega-conotoxin). In a search for new channel blockers, we have identified a peptide toxin from funnel web spider venom, omega-Aga-IVA, which is a potent inhibitor of both calcium entry into rat brain synaptosomes and of 'P-type' calcium channels in rat Purkinje neurons. omega-Aga-IVA will facilitate characterization of brain calcium channels resistant to existing channel blockers and may assist in the design of neuroprotective drugs.

Spider toxins affecting glutamate receptors: polyamines in therapeutic neurochemistry

Polyamine amide toxins obtained from venous of spiders and wasps interact selectively with ionotropic glutamate receptors (GLU-R) of vertebrate central nervous systems. The sites and modes of action of these polyamine amide toxins are reviewed with particular reference to their structure-activity relationships. Qualitatively, their effects on GLU-R are identical to those exerted by polyamines such as spermine, but the polyamine amides are more potent. These compounds (a) potentiate and (b) antagonize GLU-R, the latter arising through open channel block. For the N-methyl-D-aspartate receptor this non-competitive antagonism probably arises through binding of toxin to the Mg2+ site(s) located in the channel gated by this receptor. Similarities and differences between GLU-R in vertebrates and in invertebrates with respect to their interactions with polyamines and polyamine amide toxins are discussed. In both groups the low specificity of these compounds is illustrated by their antagonism at nicotinic acetylcholine receptors in addition to GLU-R. Electrophysiological studies, including those employing Xenopus oocytes, are reviewed and future prospects for the use of polyamine amides in therapy are discussed.

The spider toxin, argiotoxin636, binds to a Mg2+ site on the N-methyl-D-aspartate receptor complex

1. The mechanism of action of the arylalkylamine spider toxin, argiotoxin636, on the N-methyl-D-aspartate (NMDA) receptor was investigated by use of [3H]-dizocilpine binding to well-washed membranes obtained from rat brain. 2. Argiotoxin636 decreased [3H]-dizocilpine binding with an apparent potency of about 3 microM. The inhibition of [3H]-dizocilpine by argiotoxin636 was insensitive to the concentration of glutamate, glycine and spermidine in the assay. 3. Argiotoxin636 alone had no effect on the dissociation of [3H]-dizocilpine. However, argiotoxin636 reversed the actions of Mg2+ on the dissociation of [3H]-dizocilpine by decreasing the apparent potency of Mg2+. Argiotoxin636 also reversed the action of Ca2+ on the dissociation of [3H]-dizocilpine. 4. These results suggest that argiotoxin636 exerts a novel inhibitory effect on the NMDA receptor complex by binding to one of the Mg2+ sites located within the NMDA-operated ion channel.

Paralytic and insecticidal toxins from the funnel web spider, Hololena curta

One peptide and ten acylpolyamine toxins (curtatoxins) were purified and identified from venom of Hololena curta. The acylpolyamines consist of six different polyamines which are amidated with three different aromatic acids: (3-indolyl)acetic, (4-hydroxy-3-indolyl)acetic and 2.5-dihydroxybenzoic acids. These acylpolyamines instantly paralyze lepidopteran larvae following injection. The most potent insecticidal peptide in H. curta venom contains 38 amino acids and is lethal at 4 micrograms/g when injected into Manduca sexta larvae.