Proton nuclear magnetic resonance studies on huwentoxin-I from the venom of the spider Selenocosmia huwena: 2. Three-dimensional structure in solution

Disulfide-constrained peptide scaffolds enable a robust peptide-therapeutic discovery platform

Peptides present an alternative modality to immunoglobulin domains or small molecules for developing therapeutics to either agonize or antagonize cellular pathways associated with diseases. However, peptides often suffer from poor chemical and physical stability, limiting their therapeutic potential. Disulfide-constrained peptides (DCP) are naturally occurring and possess numerous desirable properties, such as high stability, that qualify them as drug-like scaffolds for peptide therapeutics. DCPs contain loop regions protruding from the core of the molecule that are amenable to peptide engineering via direct evolution by use of phage display technology. In this study, we have established a robust platform for the discovery of peptide therapeutics using various DCPs as scaffolds. We created diverse libraries comprising seven different DCP scaffolds, resulting in an overall diversity of 2 x 1011. The effectiveness of this platform for functional hit discovery has been extensively evaluated, demonstrating a hit rate comparable to that of synthetic antibody libraries. By utilizing chemically synthesized and in vitro folded peptides derived from selections of phage displayed DCP libraries, we have successfully generated functional inhibitors targeting the HtrA1 protease. Through affinity maturation strategies, we have transformed initially weak binders against Notch2 with micromolar Kd values to high-affinity ligands in the nanomolar range. This process highlights a viable hit-to-lead progression. Overall, our platform holds significant potential to greatly enhance the discovery of peptide therapeutics.

Recombinant Production, NMR Solution Structure, and Membrane Interaction of the Phα1β Toxin, a TRPA1 Modulator from the Brazilian Armed Spider Phoneutria nigriventer

Phα1β (PnTx3-6) is a neurotoxin from the spider Phoneutria nigriventer venom, originally identified as an antagonist of two ion channels involved in nociception: N-type voltage-gated calcium channel (Ca_V2.2) and TRPA1. In animal models, Phα1β administration reduces both acute and chronic pain. Here, we report the efficient bacterial expression system for the recombinant production of Phα1β and its ¹⁵N-labeled analogue. Spatial structure and dynamics of Phα1β were determined via NMR spectroscopy. The N-terminal domain (Ala1-Ala40) contains the inhibitor cystine knot (ICK or knottin) motif, which is common to spider neurotoxins. The C-terminal α-helix (Asn41-Cys52) stapled to ICK by two disulfides exhibits the µs-ms time-scale fluctuations. The Phα1β structure with the disulfide bond patterns Cys1-5, Cys2-7, Cys3-12, Cys4-10, Cys6-11, Cys8-9 is the first spider knottin with six disulfide bridges in one ICK domain, and is a good reference to other toxins from the ctenitoxin family. Phα1β has a large hydrophobic region on its surface and demonstrates a moderate affinity for partially anionic lipid vesicles at low salt conditions. Surprisingly, 10 µM Phα1β significantly increases the amplitude of diclofenac-evoked currents and does not affect the allyl isothiocyanate (AITC)-evoked currents through the rat TRPA1 channel expressed in Xenopus oocytes. Targeting several unrelated ion channels, membrane binding, and the modulation of TRPA1 channel activity allow for considering Phα1β as a gating modifier toxin, probably interacting with S1-S4 gating domains from a membrane-bound state.

Biotin conjugated organic molecules and proteins for cancer therapy: A review

The main transporter for biotin is sodium dependent multivitamin transporter (SMVT), which is overexpressed in various aggressive cancer cell lines such as ovarian (OV 2008, ID8), leukemia (L1210FR), mastocytoma (P815), colon (Colo-26), breast (4T1, JC, MMT06056), renal (RENCA, RD0995), and lung (M109) cancer cell lines. Furthermore, its overexpression was found higher to that of folate receptor. Therefore, biotin demand in the rapidly growing tumors is higher than normal tissues. Several biotin conjugated organic molecules has been reported here for selective delivery of the drug in cancer cell. Biotin conjugated molecules are showing higher fold of cytotoxicity in biotin positive cancer cell lines than the normal cell. Nanoparticles and polymer surface modified drugs and biotin mediated cancer theranostic strategy was highlighted in this review. The cytotoxicity and selectivity of the drug in cancer cells has enhanced after biotin conjugation.

Characterization of ion channels on subesophageal ganglion neurons from Chinese tarantula Ornithoctonus huwena: Exploring the myth of the spider insensitive to its venom

Chinese tarantula Ornithoctonus huwena is one of the most venomous spiders distributing in the hilly areas of southern China. In this study, using whole-cell patch-clamp technique we investigated electrophysiological and pharmacological properties of ion channels from tarantula subesophageal ganglion neurons. It was found that the neurons express multiple kinds of ion channels at least including voltage-gated calcium channels, TTX-sensitive sodium channels and two types of potassium channels. They exhibit pharmacological properties similar to mammalian subtypes. Spider calcium channels were sensitive to ω-conotoxin GVIA and diltiazem, two well-known inhibitors of mammalian neuronal high-voltage-activated (HVA) subtypes. 4-Aminopyridine and tetraethylammonium could inhibit spider outward transient and delayed-rectifier potassium channels, respectively. Huwentoxin-I and huwentoxin-IV are two abundant toxic components in the venom of Ornithoctonus huwena. Interestingly, although in our previous work they inhibit HVA calcium channels and TTX-sensitive sodium channels from mammalian sensory neurons, respectively, they fail to affect the subtypes from spider neurons. Moreover, the crude venom has no effect on delayed-rectifier potassium channels and only slightly reduces transient outward potassium channels with an IC50 value of ∼51.3 mg/L. Therefore, our findings provide important evidence for ion channels from spiders having an evolution as self-defense and prey mechanism.

Functional expression of spider neurotoxic peptide huwentoxin-I in E. coli

The coding sequence of huwentoxin-I, a neurotoxic peptide isolated from the venom of the Chinese spider Ornithoctonus huwena, was amplified by PCR using the cDNA library constructed from the spider venom glands. The cloned fragment was inserted into the expression vector pET-40b and transformed into the E. coli strain BL21 (DE3). The expression of a soluble fusion protein, disulfide interchange protein (DsbC)-huwentoxin-I, was auto-induced in the periplasm of E. coli in the absence of IPTG. After partial purification using a Ni-NTA column, the expressed fusion protein was digested using enterokinase to release heteroexpressed huwentoxin-I and was further purified using RP-HPLC. The resulting peptide was subjected to gel electrophoresis and mass spectrometry analysis. The molecular weight of the heteroexpressed huwentoxin-I was 3750.69, which is identical to that of the natural form of the peptide isolated from spider venom. The physiological properties of the heteroexpressed huwentoxin-I were further analyzed using a whole-cell patch clamp assay. The heteroexpressed huwentoxin-I was able to block currents generated by human Na(v1.7) at an IC₅₀ of 640 nmole/L, similar to that of the natural huwentoxin-I, which is 630 nmole/L.

Effect of Huwentoxin-I on the Fas and TNF apoptosis pathway in the hippocampus of rat with global cerebral ischemia

Neuronal injury is the most important reason for various brain injuries. Cytosolic Ca(2+) overloading has been proposed as one of the main cellular processes leading to neuronal death during cerebral ischemia. It is well accepted that Ca(2+) channel blockers can protect cerebral neurons from ischemic injury. In the present studies, we investigated the molecular mechanism for the neuro-protective effect of Huwentoxin-I (HWTX-I), a spider toxin selectively blocking N-type voltage-dependent Ca((2+)) channel, on rat models with global cerebral ischemia-reperfusion injury. Our studies demonstrated that HWTX-I could maintain the morphological stability of pyramidal cells in this model. Furthermore, HWTX-I could decrease the concentration of malon-dialdehyde, but increase the activity of superoxide dismutase and glutathione peroxidase. It also reduced the expression level of related factors of Fas and tumor necrosis factor death receptor apoptosis pathways in the hippocampus. In summary, HWTX-I has an obvious neuroprotective effect, which may act through its inhibition on a certain apoptosis pathway.

The cross channel activities of spider neurotoxin huwentoxin-I on rat dorsal root ganglion neurons

In this paper, we investigated the action of huwentoxin-I (HWTX-I) purified from the venom of the Chinese bird spider Ornithoctonus huwena on Ca(2+), Na(+) channels of adult rat dorsal root ganglion (DRG) neurons. The results showed that huwentoxin-I could reduce the peak currents of N-type Ca(2+) channels (IC(50) approximately 100 nM) and TTX-S Na(+) channels (IC(50) approximately 55 nM), whereas no effect was detected on TTX-R Na(+) channels. The comparative studies indicated that the selectivity of HWTX-I on Ca(2+) channels was higher that of MVIIA and approximately the same as that of GVIA. HWTX-I is the first discovered toxin with the cross channel activities from the spider O. huwena venom similar to micro O-conotoxins MrVIA and MrVIB.

Solution structure of PcFK1, a spider peptide active against Plasmodium falciparum

Psalmopeotoxin I (PcFK1) is a 33-amino-acid residue peptide isolated from the venom of the tarantula Psalmopoeus cambridgei. It has been recently shown to possess strong antiplasmodial activity against the intra-erythrocyte stage of Plasmodium falciparum in vitro. Although the molecular target for PcFK1 is not yet determined, this peptide does not lyse erythrocytes, is not cytotoxic to nucleated mammalian cells, and does not inhibit neuromuscular function. We investigated the structural properties of PcFK1 to help understand the unique mechanism of action of this peptide and to enhance its utility as a lead compound for rational development of new antimalarial drugs. In this paper, we have determined the three-dimensional solution structure by (1)H two-dimensional NMR means of recombinant PcFK1, which is shown to belong to the ICK structural superfamily with structural determinants common to several neurotoxins acting as ion channels effectors.

Sequence-specific assignment of 1H-NMR resonance and determination of the secondary structure of Jingzhaotoxin-I

Jingzhaotoxin-I (JZTX-I) purified from the venom of the spider Chilobrachys jingzhao is a novel neurotoxin preferentially inhibiting cardiac sodium channel inactivation by binding to receptor site 3. The structure of this toxin in aqueous solution was investigated using 2-D 1H-NMR techniques. The complete sequence-specific assignments of proton resonance in the 1H-NMR spectra of JZTX-I were obtained by analyzing a series of 2-D spectra, including DQF-COSY, TOCSY and NOESY spectra, in H2O and D2O. All the backbone protons except for Gln4 and more than 95% of the side-chain protons were identified by d alphaN, d alphadelta, d betaN and d NN connectivities in the NOESY spectrum. These studies provide a basis for the further determination of the solution conformation of JZTX-I. Furthermore, the secondary structure of JZTX-I was identified from NMR data. It consists mainly of a short triple-stranded antiparallel beta-sheet with Trp7-Cys9, Phe20-Lys23 and Leu28-Trp31. The characteristics of the secondary structure of JZTX-I are similar to those of huwentoxin-I (HWTX-I) and hainantoxin-IV (HNTX-IV), whose structures in solution have previously been reported.

Antinociceptive effects of intrathecally administered huwentoxin-I, a selective N-type calcium channel blocker, in the formalin test in conscious rats

The present study was undertaken to elucidate the antinociceptive effect of intrathecal administration of huwentoxin-I (HWTX-I), a N-type calcium channel blocker from the venom of the Chinese bird spider Ornithoctonus huwena (Wang) [=Selenocosmia huwena wang], by comparison with omega-Conotoxin-MVIIA (omega-CTX-MVIIA) and morphine hydrochloride in the formalin test in conscious rats. Similar to omega-CTX-MVIIA and morphine, intrathecal pre-treatment with HWTX-I resulted in suppression of nociceptive behavior in a dose-dependent manner. The ED50 values of HWTX-I and omega-CTX-MVIIA were 0.28 and 0.19 microg/kg, respectively. It was also found that, at lower doses (0.1 and 0.5 microg/kg), the antinociceptive effect of HWTX-I was identical to that of omega-CTX-MVIIA, while omega-CTX-MVIIA acted more remarkably than HWTX-I at higher dose (1.0 microg/kg). However, the antinociception induced by omega-CTX-MVIIA were companied with motor dysfunction, and these side-effects became more evident with the doses of omega-CTX-MVIIA increasing. In contrast, HWTX-I did not show these side-effects at the doses of 0.5-1.0 microg/kg. Compared with HWTX-I and omega-CTX-MVIIA, the analgesic effect of intrathecal morphine hydrochloride was initiated faster, but lasted for a shorter time (about 2-3 h at 1.0 microg/kg) than that of HWTX-I and omega-CTX-MVIIA (about 4- 5 h at 1.0 microg/kg). Therefore, the present results show that, like omega-CTX-MVIIA, the intrathecal administration of HWTX-I is effective in antinociception in the rat model of the formalin test.

An overview of peptide toxins from the venom of the Chinese bird spider Selenocosmia huwena Wang [=Ornithoctonus huwena (Wang)]

The bird spider Selenocosmia huwena Wang [=Ornithoctonus huwena (Wang)] is one of the most venomous spiders in China. The venom of this spider contains a mixture of compounds with different types of biological activity. About 400 proteins and peptides from the venom can be separated and detected by 2D electrophoresis. Of these, 14 peptide toxins have been purified and characterized from the venom of this spider, with several peptide toxins exhibiting structural similarity but high functional diversity. Most of these huwentoxins (HWTX) contain 30-40 amino acids with three disulfide bonds and adopt an "inhibitor cystine-knot" (ICK) motif in their three dimensional structure, except for huwentoxin-II (HWTX-II) which adopts a novel scaffold different from the ICK motif. As a group, the toxins possess quite different biological activities including inhibition of voltage-gated calcium and sodium channels, insecticidal activity, lectin-like agglutination, and inhibition of trypsin. Eight cDNAs encoding seven toxins, HWTX-I, -II, -III, -IIIa, -IV -V, and, -VII and one lectin, S. huwena lectin-I (SHL-I), have been cloned and sequenced. Comparison of the cDNA sequences of the eight peptides from S. huwena indicates that they can be classified into two different superfamilies according to the "prepro" region of their cDNA sequences.

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

Delta-conotoxin EVIA, from Conus ermineus, is a 32-residue polypeptide cross-linked by three disulfide bonds forming a four-loop framework. delta-Conotoxin EVIA is the first conotoxin known to inhibit sodium channel inactivation in neuronal membranes from amphibians and mammals (subtypes rNa(v)1.2a, rNa(v)1.3, and rNa(v)1.6), without affecting rat skeletal muscle (subtype rNa(v)1.4) and human cardiac muscle (subtype hNa(v)1.5) sodium channel (Barbier, J., Lamthanh, H., Le Gall, F., Favreau, P., Benoit, E., Chen, H., Gilles, N., Ilan, N., Heinemann, S. F., Gordon, D., Ménez, A., and Molgó, J. (2004) J. Biol. Chem. 279, 4680-4685). Its structure was solved by NMR and is characterized by a 1:1 cis/trans isomerism of the Leu(12)-Pro(13) peptide bond in slow exchange on the NMR time scale. The structure of both cis and trans isomers could be calculated separately. The isomerism occurs within a specific long disordered loop 2, including residues 11-19. These contribute to an important hydrophobic patch on the surface of the toxin. The rest of the structure matches the "inhibitor cystine-knot motif" of conotoxins from the "O superfamily" with a high structural order. To probe a possible functional role of the Leu(12)-Pro(13) cis/trans isomerism, a Pro(13) --> Ala delta-conotoxin EVIA was synthesized and shown to exist only as a trans isomer. P13A delta-conotoxin EVIA was estimated only two times less active than the wild-type EVIA in binding competition to rat brain synaptosomes and when injected intracerebroventricularly into mice.

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.

Structure and function of δ-atracotoxins: lethal neurotoxins targeting the voltage-gated sodium channel

Delta-atracotoxins (delta-ACTX), isolated from the venom of Australian funnel-web spiders, are responsible for the potentially lethal envenomation syndrome seen following funnel-web spider envenomation. They are 42-residue polypeptides with four disulfides and an "inhibitor cystine-knot" motif with structural but not sequence homology to a variety of other spider and marine snail toxins. Delta-atracotoxins induce spontaneous repetitive firing and prolongation of action potentials resulting in neurotransmitter release from somatic and autonomic nerve endings. This results from a slowing of voltage-gated sodium channel inactivation and a hyperpolarizing shift of the voltage-dependence of activation. This action is due to voltage-dependent binding to neurotoxin receptor site-3 in a similar, but not identical, fashion to scorpion alpha-toxins and sea anemone toxins. Unlike other site-3 neurotoxins, however, delta-ACTX bind with high affinity to both cockroach and mammalian sodium channels but low affinity to locust sodium channels. At present the pharmacophore of delta-ACTX is unknown but is believed to involve a number of basic residues distributed in a topologically similar manner to scorpion alpha-toxins and sea anemone toxins despite distinctly different protein scaffolds. As such, delta-ACTX provide us with specific tools with which to study sodium channel structure and function and determinants for phyla- and tissue-specific actions of neurotoxins interacting with site-3.

Function and solution structure of hainantoxin-I, a novel insect sodium channel inhibitor from the Chinese bird spider Selenocosmia hainana

Hainantoxin-I is a novel peptide toxin, purified from the venom of the Chinese bird spider Selenocosmia hainana (=Ornithoctonus hainana). It includes 33 amino acid residues with a disulfide linkage of I-IV, II-V and III-VI, assigned by partial reduction and sequence analysis. Under two-electrode voltage-clamp conditions, hainantoxin-I can block rNa(v)1.2/beta(1) and the insect sodium channel para/tipE expressed in Xenopus laevis oocytes with IC(50) values of 68+/-6 microM and 4.3+/-0.3 microM respectively. The three-dimensional solution structure of hainantoxin-I belongs to the inhibitor cystine knot structural family determined by two-dimensional (1)H nuclear magnetic resonance techniques. Structural comparison of hainantoxin-I with those of other toxins suggests that the combination of the charged residues and a vicinal hydrophobic patch should be responsible for ligand binding. This is the first report of an insect sodium channel blocker from spider venom and it provides useful information for the structure-function relationship studies of insect sodium channels.

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.

Purification and characterization of Hainantoxin-V, a tetrodotoxin-sensitive sodium channel inhibitor from the venom of the spider Selenocosmia hainana

A neurotoxic peptide, named Hainantoxin-V (HNTX-V), was isolated from the venom of the Chinese bird spider Selenocosmia hainana. The complete amino acid sequence of HNTX-V has been determined by Edman degradation and found to contain 35 amino acid residues with three disulfide bonds. Under whole-cell patch-clamp mode, HNTX-V was proved to inhibit the tetrodotoxin-sensitive (TTX-S) sodium currents while it had no any effects on tetrodotoxin-resistant (TTX-R) sodium currents on adult rat dorsal root ganglion neurons. The inhibition of TTX-S sodium currents by HNTX-V was tested to be concentrate-dependent with the IC(50) value of 42.3nM. It did not affect the activation and inactivation kinetics of currents and did not have the effect on the active threshold of sodium channels and the voltage of peak inward currents. However, 100nM HNTX-V caused a 7.7mV hyperpolarizing shift in the voltage midpoint of steady-state sodium channel inactivation. The results indicated that HNTX-V inhibited mammalian voltage-gated sodium channels through a novel mechanism distinct from other spider toxins such as delta-ACTXs, micro -agatoxins I-VI which bind to receptor site three to slow the inactivation kinetics of sodium currents.

Structure and dynamics of the potato carboxypeptidase inhibitor by 1H and 15N NMR

The solution structure and backbone dynamics of the recombinant potato carboxypeptidase inhibitor (PCI) have been characterized by NMR spectroscopy. The structure, determined on the basis of 497 NOE-derived distance constraints, is much better defined than the one reported in a previous NMR study, with an average pairwise backbone root-mean-square deviation of 0.5 A for the well-defined region of the protein, residues 7-37. Many of the side-chains show now well-defined conformations, both in the hydrophobic core and on the surface of the protein. Overall, the solution structure of free PCI is similar to the one that it shows in the crystal of the complex with carboxypeptidase A. However, some local differences are observed in regions 15-21 and 27-29. In solution, the six N-terminal and the two C-terminal residues are rather flexible, as shown by 15N backbone relaxation measurements. The flexibility of the latter segment may have implications in the binding of the inhibitor by the enzyme. All the remaining residues in the protein are essentially rigid (S2 > 0.8) with the exception of two of them at the end of a short 3/10 helix. Despite the small size of the protein, a number of amide protons are protected from exchange with solvent deuterons. The slowest exchanging protons are those in a small two-strand beta-sheet. The unfolding free energies, as calculated from the exchange rates of these protons, are around 5 kcal/mol. Other protected amide protons are located in the segment 7-12, adjacent to the beta-sheet. Although these residues are not in an extended conformation in PCI, the equivalent residues in structurally homologous proteins form a third strand of the central beta-sheet. The amide protons in the 3/10 helix are only marginally protected, indicating that they exchange by a local unfolding mechanism, which is consistent with the increase in flexibility shown by some of its residues. Backbone alignment-based programs for folding recognition, as opposite to disulfide-bond alignments, reveal new proteins of unrelated sequence and function with a similar structure.

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.

The structure of spider toxin huwentoxin-II with unique disulfide linkage: evidence for structural evolution

The three-dimensional structure of huwentoxin-II (HWTX-II), an insecticidal peptide purified from the venom of spider Selenocosmia huwena with a unique disulfide bond linkage as I-III, II-V, and IV-VI, has been determined using 2D (1)H-NMR. The resulting structure of HWTX-II contains two beta-turns (C4-S7 and K24-W27) and a double-stranded antiparallel beta-sheet (W27-C29 and C34-K36). Although the C-terminal double-stranded beta-sheet cross-linked by two disulfide bonds (II-V and IV-VI in HWTX-II, II-V and III-VI in the ICK molecules) is conserved both in HWTX-II and the ICK molecules, the structure of HWTX-II is unexpected absence of the cystine knot because of its unique disulfide linkage. It suggests that HWTX-II adopts a novel scaffold different from the ICK motif that is adopted by all other spider toxin structures elucidated thus far. Furthermore, the structure of HWTX-II, which conforms to the disulfide-directed beta-hairpin (DDH) motif, not only supports the hypothesis that the ICK is a minor elaboration of the more ancestral DDH motif but also suggests that HWTX-II may have evolved from the same structural ancestor.

The effect of Huwentoxin-I on Ca(2+) channels in differentiated NG108-15 cells, a patch-clamp study

Huwentoxin-I (HWTX-I), a 3.75 kDa peptide toxin isolated from the venom of the spider Selenocosmia huwena, was found to be a reversible presynaptic inhibitor by our previous work. Using whole-cell patch clamp methods, we found that HWTX-I had no significant effect on the TTX-sensitive Na(+) current or the delayed rectifier K(+) current (K(r)) in low-serum medium cultured NG108-15 cells, but High-Voltage-Activated Ca(2+) channel expressed in prostaglandin E(1) differentiated NG108-15 cells could be potently inhibited by HWTX-I (EC(50) approximately 100 nM), while it hardly affected low-voltage-activated Ca(2+) channel. Among types of high-voltage-activated Ca(2+) channel, HWTX-I selectively inhibited N-type Ca(2+) channel and had only very weak effect on L-type Ca(2+) channel in prostaglandin E(1) differentiated NG108-15 cells.

Assignment of the disulfide bonds of huwentoxin-II by Edman degradation sequencing and stepwise thiol modification

A novel strategy combining Edman degradation and thiol modification was developed to assign the three disulfides of huwentoxin-II (HWTX-II), an insecticidal peptide purified from the venom of the spider Selenocosmia huwena. Phenylthiohydantoin (Pth) derivatives of Cys and the elimination product, dehydroalanine (DeltaSer), can be observed in the Cys cycles during Edman degradation of native HWTX-II. The appearance of two products indicates that the disulfides of HWTX-II were split and that the free thiol group of the second half cystine has been generated. Information about the nature of the disulfide bridges of HWTX-II could be obtained from the sequencing signal if the nascent thiols were modified stepwise by 4-vinylpyridine. Using this method the disulfide bridges of HWTX-II were assigned as Cys4-Cys18, Cys8-Cys29 and Cys23-Cys34, which is different from that seen in HWTX-I, a neurotoxic peptide from the same spider. Using this strategy, one can assign the disulfide bonds of small proteins by sequencing and modification n - 1 times, where n is the number of disulfide bonds in the protein. The above assignment of the disulfide bonds of HWTX-II was confirmed by MALDI-TOF MS of tryptic fragments of HWTX-II. Some disulfide interchanging during proteolysis was observed by monitoring the kinetics of proteolysis of HWTX-II by MALDI-TOF MS.

The cystine knot motif in toxins and implications for drug design

The cystine knot structural motif is present in peptides and proteins from a variety of species, including fungi, plants, marine molluscs, insects and spiders. It comprises an embedded ring formed by two disulfide bonds and their connecting backbone segments which is threaded by a third disulfide bond. It is invariably associated with nearby beta-sheet structure and appears to be a highly efficient motif for structure stabilization. Because of this stability it makes an ideal framework for molecular engineering applications. In this review we summarize the main structural features of the cystine knot motif, focussing on toxin molecules containing either the inhibitor cystine knot or the cyclic cystine knot. Peptides containing these motifs are 26-48 residues long and include ion channel blockers, haemolytic agents, as well as molecules having antiviral and antibacterial activities. The stability of peptide toxins containing the cystine knot motif, their range of bioactivities and their unique structural scaffold can be harnessed for molecular engineering applications and in drug design. Applications of cystine knot molecules for the treatment of pain, and their potential use in antiviral and antibacterial applications are described.

The presynaptic activity of huwentoxin-I, a neurotoxin from the venom of the chinese bird spider Selenocosmia huwena

Three different types of isolated nerve-synapse preparations, guinea pig ileum, rat vas deferens and toad heart, were used to investigate the physiological activity of Huwentoxin-I, a neurotoxin from the venom of the spider Selenocosmia huwena. The twitch response of isolated guinea pig ileum induced by electrical stimulus can be inhibited by HWTX-I. After blockage, contraction of the ileum can be induced by exogenously applied acetylcholine. HWTX-I caused the inhibition of the twitch response to electrical nerve stimulation in the rat vas deferens. After the twitch was completely inhibited, noradrenaline triggered rhythmic contraction of the vas deferens. The inhibitory effect on heart of toad induced by stimulating sympathetic-vagus nerve can be reversed by HWTX-I, although exogenously applied acetylcholine still acts as an effective inhibitor. All of these results support the conclusion that HWTX-I has the presynaptic activity that effects the release of neurotransmitter from the nerve endings of both the cholinergic synapse and the adrenergic synapse.

Indentification of venom proteins of spider S. huwena on two-dimensional electrophoresis gel by N-terminal microsequencing and mass spectrometric peptide mapping

Venom proteins of the spider Selenocosmia huwena were separated by two-dimensional gel electrophoresis, with the separation in the first dimension on a wide range of immobilized pH (3-10) gradients. Over 300 protein spots were presented on a silver-stained 2D gel. The protein spots with molecular weight >10 kDa were analyzed, after electrotransferring to polyvinyldene difluoride (PVDF) membrane, by N-terminal microseqencing. Some of the silver-stained protein spots with molecular weight over 10 kDa were analyzed and identified by employing an improved procedure of mass spectrometric peptide mapping, including (1) in-gel reduction, alkylation, and enzymatic digestion; (2) extraction and desalting by using the pipette tip containing a small C18 microcolumn (Ziptip); and (3) direct MAIDI-TOF mass analysis and protein database searching. Several known toxins such as HWTX-I, HWTX-II, HWTX-IV, and SHL-I were identified and some new components were found among these protein spots.

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

A new toxin (SGTx1) was purified from the venom of the spider Scodra griseipes by a combination of gel filtration and reverse-phase chromatography. The complete amino acid sequence of SGTx1, TCRYLFGGCKTTADCCKHLACRSDGKYCAWDGTF, was established by direct automated Edman degradation, and is in perfect agreement with the molecular mass of 3775 Da found by mass spectrometry. The primary structure of SGTx1 exhibited sequence identity with other spider toxins such as hanatoxin (76%), TxP5 toxin (32%) and huwentoxin (26%). The six cysteines in the sequence suggested three disulfide bridges, the presence of which was demonstrated by mass spectrometry after dithiothreitol reduction. Analysis of secondary structure using circular dichroism spectrometry yielded more than 50% beta-sheet and about 15-20% beta-turn. The extent of the beta-content and the presence of disulfide bridges suggest a structure of interconnected beta-strands. In addition, a study of membrane/toxin interactions was carried out by reconstitution in planar lipid bilayers and by antibacterial assays. SGTx1 displays moderate pore-forming ability (conductance of about 100 pS in 1 M NaCl), but antibacterial activity was not observed against Gram-positive or Gram-negative strains. As a preliminary assay, the activity of SGTx1 was investigating using electrophysiological measurements. At 0.15 microM, SGTx1 reversibly inhibits more than 40% of outward potassium currents in rat cerebellum granular cells. This result is reminiscent with the effect described for hanatoxin extracted from the venom of Grammostola spatulata.

Polypeptide neurotoxins from spider venoms

Spider venoms contain a variety of toxic components. The polypeptide toxins are divided into low and high molecular mass types. Small polypeptide toxins interacting with cation channels display spatial structure homology. They can affect the functioning of calcium, sodium, or potassium channels. A family of high molecular mass toxic proteins was found in the venom of the spider genus Latrodectus. These neurotoxins, latrotoxins, cause a massive transmitter release from a diversity of nerve endings. The latrotoxins are proteins of about 1000 amino acid residues and share a high level of structure identity. The structural and functional properties of spider polypeptide toxins are reviewed in this paper.

Oxidative folding of reduced and denatured huwentoxin-I

Huwentoxin-I, a neurotoxic peptide with 33 amino acid residues and three disulfide bonds, was used to investigate the pathway of reduction/denaturation and of oxidative folding in small proteins with multiple disulfide bonds. Titration of thiol groups, reversed-phase HPLC, 1D NMR spectroscopy, and biological activity assays were used to monitor the extent of reduction/ denaturation and renaturation of the toxin. The reduction and denaturation of huwentoxin-I resulted in a 100% loss of bioactivity as measured in a mouse phrenic nerve-diaphragm preparation. About 90% of full biological activity could be restored under optimized conditions of oxidative refolding of the reduced peptide. Several reaction conditions employing air oxidation, oxidized and reduced glutathione (GSSG and GSH), and cystine/cysteine were investigated in order to find optimal conditions for renaturation of huwentoxin-I. The best renaturation yield was achieved in 0.1 mM GSSG and 1 mM GSH at pH 8.5 and 4 degrees C over 24 hr. High concentrations of glutathione and high temperatures reduced renaturation yields. Oxidative refolding of huwentoxin-I in air requires about 6 days for maximal yields and is inhibited by EDTA.

Solution structure of the major alpha-amylase inhibitor of the crop plant amaranth

alpha-Amylase inhibitor (AAI), a 32-residue miniprotein from the Mexican crop plant amaranth (Amaranthus hypochondriacus), is the smallest known alpha-amylase inhibitor and is specific for insect alpha-amylases (Chagolla-Lopez, A., Blanco-Labra, A., Patthy, A., Sanchez, R., and Pongor, S. (1994) J. Biol. Chem. 269, 23675-23680). Its disulfide topology was confirmed by Edman degradation, and its three-dimensional solution structure was determined by two-dimensional 1H NMR spectroscopy at 500 MHz. Structural constraints (consisting of 348 nuclear Overhauser effect interproton distances, 8 backbone dihedral constraints, and 9 disulfide distance constraints) were used as an input to the X-PLOR program for simulated annealing and energy minimization calculations. The final set of 10 structures had a mean pairwise root mean square deviation of 0.32 A for the backbone atoms and 1.04 A for all heavy atoms. The structure of AAI consists of a short triple-stranded beta-sheet stabilized by three disulfide bonds, forming a typical knottin or inhibitor cystine knot fold found in miniproteins, which binds various macromolecular ligands. When the first intercystine segment of AAI (sequence IPKWNR) was inserted into a homologous position of the spider toxin Huwentoxin I, the resulting chimera showed a significant inhibitory activity, suggesting that this segment takes part in enzyme binding.

Three-dimensional structure of Selenocosmia huwena lectin-I (SHL-I) from the venom of the spider Selenocosmia huwena by 2D-NMR

The three-dimensional structure of native SHL-I, a lectin from the venom of the Chinese bird spider Selenocosmia huwena, has been determined from two-dimensional 1H NMR spectroscopy recorded at 500 and 600 MHz. The best 10 structures have NOE violation <0.3 A, dihedral violation <2 deg, and average root-mean-square differences of 0.85 + 0.06 A over backbone atoms. The structure consists of a three-stranded antiparallel beta-sheet and three turns. The three disulfide bridges and three-stranded antiparallel beta-sheet form a inhibitor cystine knot motif which is adopted by several other small proteins, such as huwentoxin-I, omega-conotoxin, and gurmarin. The C-terminal fragment from Leu28 to Trp32 adopts two sets of conformations corresponding to the cis and trans conformations of Pro31. The structure of SHL-I also has high similarity with that of the N-terminus of hevein, a lectin from rubber-tree latex.

1H NMR study of robustoxin, the lethal neurotoxin from the funnel web spider Atrax robustus

Robustoxin, the lethal neurotoxin from the Sydney funnel web spider Atrax robustus, is a polypeptide of 42 residues cross-linked by four disulfide bonds. This paper describes the sequence-specific assignment of resonances in the 1H nuclear magnetic resonance spectrum of robustoxin in aqueous solution. Several broad backbone amide resonances were encountered in spectra recorded at 27 degrees C, making the assignments at that temperature incomplete. In spectra recorded at lower temperatures these amide resonances became sharper, but others that were sharp at 27 degrees C became broad, indicative of conformational averaging on the millisecond timescale for certain regions of the structure. Nevertheless, it was possible to establish that robustoxin contains a small, triple-stranded, antiparallel beta-sheet and several reverse turns, but no alpha-helix. These observations indicate that this toxin may adopt the inhibitor cystine knot structure found in polypeptides from a diverse range of species, including a number of spiders. Analysis of the pH dependence of the spectrum yielded pKa values for Tyr22 and Tyr25, one of the three carboxyl groups, and the Lys residues.

Assignment of the three disulfide bonds of Selenocosmia huwena lectin-I from the venom of spider Selenocosmia huwena

The positions of the disulfide bonds of Selenocosmia huwena lectin-I (SHL-I) from the venom of the Chinese bird spider S. huwena have been determined. The existence of three disulfide bonds in the native SHL-I was proved by matrix-assisted laser desorption ionization time-of-flight mass spectroscopic analysis. To map the disulfide bonds, native SHL-I was proteolytically digested. The resulting peptides were separated by reverse phase high-performance liquid chromatography. Matrix-assisted laser desorption ionization time-of-flight mass spectroscopic analysis indicated the presence of one disulfide bond Cys7-Cys19. The partially reduced peptides by using Tris-(2-carboxyethyl)-phosphine at pH 3.0 were purified by reverse phase high-performance liquid chromatography. Four M Guanidine-HCl was found to increase the yields of partially reduced peptides prominently. The free thiols were carboxamidomethlate by iodoacetamide. The specific location of another disulfide bond Cys2-Cys14 was proved by comparing N-terminal sequencing analysis of the partially reduced and alkylated SHL-I with that of the intact peptide. Finally, the three disulfide linkage of SHL-I could be assigned as Cys2-Cys14, Cys7-Cys19, Cys13-Cys26.

The cystine knot structure of ion channel toxins and related polypeptides

An increasing number of ion channel toxins and related polypeptides have been found to adopt a common structural motif designated the inhibitor cystine knot motif (Pallaghy P. K., Nielsen, K. J., Craik, D. J., Norton, R. S. (1994) A common structural motif incorporating a cystine knot and triple-stranded beta-sheet in toxic and inhibitory polypeptides. Protein Science 3, 1833-1839). These globular, disulfide-stabilized molecules come from phylogenetically diverse sources, including spiders, cone shells, plants and fungi, and have various functions, although many target voltage-gated ion-channels. The common motif consists of a cystine knot and a triple-stranded, anti-parallel beta-sheet. Examples of ion-channel toxins known to adopt this structure are the omega-conotoxins and omega-agatoxins, and, more recently, robustoxin, versutoxin and protein 5 from spiders, as well as kappa-conotoxin PVIIA and conotoxin GS from cone shells. The variations on the motif structure exemplified by these structures are described here. We also consider the sequences of several polypeptides that might adopt this fold, including SNX-325 from a spider, delta-conotoxin PVIA and the muO-conotoxins from cone shells, and various plant and fungal polypeptides. The interesting case of the two- and three-disulfide bridged binding domains of the cellobiohydrolases from the fungus Trichoderma reesei is also discussed. The compact and robust nature of this motif makes it an excellent scaffold for the design and engineering of novel polypeptides with enhanced activity against existing targets, or with activity against novel targets.

Solution structure of robustoxin, the lethal neurotoxin from the funnel-web spider Atrax robustus

The solution structure of robustoxin, the lethal neurotoxin from the Sydney funnel-web spider Atrax robustus, has been determined from 2D 1H NMR data. Robustoxin is a polypeptide of 42 residues cross-linked by four disulphide bonds, the connectivities of which were determined from NMR data and trial structure calculations to be 1-15, 8-20, 14-31 and 16-42 (a 1-4/2-6/3-7/5-8 pattern). The structure consists of a small three-stranded, anti-parallel beta-sheet and a series of interlocking gamma-turns at the C-terminus. It also contains a cystine knot, thus placing it in the inhibitor cystine knot motif family of structures, which includes the omega-conotoxins and a number of plant and animal toxins and protease inhibitors. Robustoxin contains three distinct charged patches on its surface, and an extended loop that includes several aromatic and non-polar residues. Both of these structural features may play a role in its binding to the voltage-gated sodium channel.