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At least 721 records · Page 40Linked to original sources
PubMed2000

Maurotoxin and the Kv1.1 channel: voltage-dependent binding upon enantiomerization of the scorpion toxin disulfide bridge Cys31-Cys34.

Maurotoxin (MTX) is a 34-amino acid polypeptide cross-linked by four disulfide bridges that has been isolated from the venom of the scorpion Scorpio maurus palmatus and characterized. Maurotoxin competed with radiolabeled apamin and kaliotoxin for binding to rat brain synaptosomes and blocked K+ currents from Kv1 channel subtypes expressed in Xenopus oocytes. Structural characterization of the synthetic toxin identified half-cystine pairings at Cys3-Cys24, Cys9-Cys29, Cys13-Cys19 and Cys31-Cys34 This disulfide bridge pattern is unique among known scorpion toxins, particularly the existence of a C-terminal '14-membered disulfide ring' (i.e. cyclic domain 31-34), We therefore studied structure-activity relationships by investigating the structure and pharmacological properties of synthetic MTX peptides either modified at the C-terminus ¿i.e. MTX(1-29), [Abu31,34]-MTX and [Cys31,34, Tyr32]D-MTX) or mimicking the cyclic C-terminal domain [i.e. MTX(31-34)]. Unexpectedly, the absence of a disulfide bridge Cys31-Cys34 in [Abu 31,34]-MTX and MTX(1-29) resulted in MTX-unrelated half-cystine pairings of the three remaining disulfide bridges for the two analogs, which is likely to be responsible for their inactivity against Kv1 channel subtypes. Cyclic MTX(31-34) was also biologically inactive. [Cys31,34, Tyr32]D-MTX, which had a 'native', MTX-related, disulfide bridge organization, but a D-residue-induced reorientation of the C-terminal disulfide bridge, was potent at blocking the Kv1.1 channel. This peptide-induced Kv1.1 blockage was voltage-dependent (a property not observed for MTX), maximal in the low depolarization range and associated with on-rate changes in ligand binding. Thus, the cyclic C-terminal domain of MTX seems to be crucial for recognition of Kv1.3, and to a lesser extent, Kv1.2 channels and it may contribute to the stabilization and strength of the interaction between the toxin and the Kv1.1 channel.

Amino Acid Sequence↗
PubMed1998

Inhibition of T-type voltage-gated calcium channels by a new scorpion toxin.

The biophysical properties of T-type voltage-gated calcium channels are well suited to pacemaking and to supporting calcium flux near the resting membrane potential in both excitable and non-excitable cells. We have identified a new scorpion toxin (kurtoxin) that binds to the alpha 1G T-type calcium channel with high affinity and inhibits the channel by modifying voltage-dependent gating. This toxin distinguishes between alpha 1G T-type calcium channels and other types of voltage-gated calcium channels, including alpha 1A, alpha 1B, alpha 1C and alpha 1E. Like the other alpha-scorpion toxins to which it is related, kurtoxin also interacts with voltage-gated sodium channels and slows their inactivation. Kurtoxin will facilitate characterization of the subunit composition of T-type calcium channels and help determine their involvement in electrical and biochemical signaling.

Animals↗
PubMed1998

Effect of Tityus serrulatus scorpion venom on the rabbit isolated corpus cavernosum and the involvement of NANC nitrergic nerve fibres.

1. The effect of Tityus serrulatus scorpion venom and its toxin components on the rabbit isolated corpus cavernosum was investigated by use of a bioassay cascade. 2. Tityus serrulatus venom (3-100 microg), acetylcholine (ACh; 0.3-30 nmol) and glyceryl trinitrate (GTN; 0.5-10 nmol) dose-dependently relaxed rabbit isolated corpus cavernosum preparations precontracted with noradrenaline (3 microM). The selective soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-alquinoxalin-1-one] (ODQ; 30 microM) increased the basal tone of the rabbit isolated corpus cavernosum and abolished the relaxations induced by the agents mentioned above. Methylene blue (30 microM) also inhibited the relaxations induced by Tityus serrulatus venom but, in contrast to ODQ, the inhibition was irreversible. 3. The non-selective NO synthase (NOS) inhibitors Nomega-nitro-L-arginine methyl ester (L-NAME; 10 microM) and NG-iminoethyl-L-ornithine (L-NIO; 30 microM) also increased the tone of the rabbit isolated corpus cavernosum and markedly reduced both ACh- and Tityus serrulatus venom-induced relaxations without affecting those evoked by GTN. The inhibitory effect was reversed by infusion of L-arginine (300 microM), but not D-arginine (300 microM). The neuronal NOS inhibitor 1-(2-trifluoromethylphenyl) imidazole (TRIM, 100 microM) did not affect either the tone of the rabbit isolated corpus cavernosum or the relaxations induced by ACh, bradykinin (Bk), Tityus serrulatus venom and GTN. TRIM was approximately 1,000 times less potent than L-NAME in inhibiting rabbit cerebellar NOS in vitro, as measured by the conversion of [3H]-L-arginine to [3H]-L-citrulline. 4. The protease inhibitor aprotinin (Trasylol; 10 microg ml[-1]) and the bradykinin B2 receptor antagonist Hoe 140 (D-Arg-[Hyp3,Thi5,D-Tic7, Oic8]-BK; 50 nM) did not affect the rabbit isolated corpus cavernosum relaxations induced by Tityus serrulatus venom. The ATP-dependent K+ channel antagonist glibenclamide (10 microm) and the Ca2+-activated K+ channel antagonists apamin (0.1 microM) and charybdotoxin (0.1 microM) also failed to affect the venom-induced relaxations. Similarly, the K+ channel blocker tetraethylammonium (TEA; 10 microM) had no effect on the venom-induced relaxations. 5. Capsaicin (3 and 10 nmol) relaxed the rabbit isolated corpus cavernosum in a dose-dependent and non-tachyphylactic manner. Ruthenium red (30 microM), an inhibitor of capsaicin-induced responses, markedly reduced the relaxations caused by capsaicin, but failed to affect those induced by Tityus serrulatus venom. L-NAME (10 microM) had no effect on the capsaicin-induced relaxations of the rabbit isolated corpus cavernosum. 6. The sodium channel blocker tetrodotoxin (TTX; 1 microM) abolished the relaxations of the rabbit isolated corpus cavernosum induced by Tityus serrulatus venom without affecting those evoked by capsaicin, ACh and GTN. Tetrodotoxin (1 microM) also promptly reversed the response to the venom when infused during the relaxation phase. 7. The bioassay cascade of the toxin components purified from Tityus serrulatus venom revealed that only fractions X, XI and XII caused dose-dependent relaxations of the rabbit isolated corpus cavernosum and these were markedly reduced by either TTX (1 microM) or L-NAME (10 microM). 8. Our results indicate that Tityus serrulatus scorpion venom (and the active fractions X, XI and XII) relaxes rabbit corpus cavernosum via the release of NO. This release is specifically triggered by the activation of capsaicin-insensitive cavernosal non-adrenergic non-cholinergic (NANC) fibres, that may possibly be nitrergic neurones. Tityus serrulatus venom may therefore provide an important tool for understanding further the mechanism of NANC nitrergic nerve activation.

Animals↗
PubMed2003

Characterization of Amm VIII from Androctonus mauretanicus mauretanicus: a new scorpion toxin that discriminates between neuronal and skeletal sodium channels.

The venom of the scorpion Androctonus mauretanicus mauretanicus was screened by use of a specific serum directed against AaH II, the scorpion alpha-toxin of reference, with the aim of identifying new analogues. This led to the isolation of Amm VIII (7382.57 Da), which gave a highly positive response in ELISA, but was totally devoid of toxicity when injected subcutaneously into mice. In voltage-clamp experiments with rat brain type II Na+ channel rNa(v)1.2 or rat skeletal muscle Na+ channel rNa(v)1.4, expressed in Xenopus oocytes, the EC50 values of the toxin-induced slowing of inactivation were: 29+/-5 and 416+/-14 nM respectively for AmmVIII and 2.6+/-0.3 nM and 2.2+/-0.2 nM, respectively, for AaH II interactions. Accordingly, Amm VIII clearly discriminates neuronal versus muscular Na+ channel. The Amm VIII cDNA was amplified from a venom gland cDNA library and its oligonucleotide sequence determined. It shows 87% sequence homology with AaH II, but carries an unusual extension at its C-terminal end, consisting of an additional Asp due to a point mutation in the cDNA penultimate codon. We hypothesized that this extra amino acid residue could induce steric hindrance and dramatically reduce recognition of the target by Amm VIII. We constructed a model of Amm VIII based on the X-ray structure of AaH II to clarify this point. Molecular modelling showed that this C-terminal extension does not lead to an overall conformational change in Amm VIII, but drastically modifies the charge repartition and, consequently, the electrostatic dipole moment of the molecule. At last, liquid-phase radioimmunassays with poly- and monoclonal anti-(AaH II) antibodies showed the loss of conformational epitopes between AaH II and Amm VIII.

Amino Acid Sequence↗
PubMed2004

Cobatoxin 1 from Centruroides noxius scorpion venom: chemical synthesis, three-dimensional structure in solution, pharmacology and docking on K+ channels.

CoTX1 (cobatoxin 1) is a 32-residue toxin with three disulphide bridges that has been isolated from the venom of the Mexican scorpion Centruroides noxius Hoffmann. Here we report the chemical synthesis, disulphide bridge organization, 3-D (three-dimensional) solution structure determination, pharmacology on K+ channel subtypes (voltage-gated and Ca2+-activated) and docking-simulation experiments. An enzyme-based cleavage of the synthetic folded/oxidized CoTX1 indicated half-cystine pairs between Cys3-Cys22, Cys8-Cys27 and Cys12-Cys29. The 3-D structure of CoTX1 (solved by 1H-NMR) showed that it folds according to the common alpha/beta scaffold of scorpion toxins. In vivo, CoTX1 was lethal after intracerebroventricular injection to mice (LD50 value of 0.5 microg/mouse). In vitro, CoTX1 tested on cells expressing various voltage-gated or Ca2+-activated (IKCa1) K+ channels showed potent inhibition of currents from rat K(v)1.2 ( K(d) value of 27 nM). CoTX1 also weakly competed with 125I-labelled apamin for binding to SKCa channels (small-conductance Ca2+-activated K+ channels) on rat brain synaptosomes (IC50 value of 7.2 microM). The 3-D structure of CoTX1 was used in docking experiments which suggests a key role of Arg6 or Lys10, Arg14, Arg18, Lys21 (dyad), Ile23, Asn24, Lys28 and Tyr30 (dyad) residues of CoTX1 in its interaction with the rat K(v)1.2 channel. In addition, a [Pro7,Gln9]-CoTX1 analogue (ACoTX1) was synthesized. The two residue replacements were selected aiming to restore the RPCQ motif in order to increase peptide affinity towards SKCa channels, and to alter the CoTX1 dipole moment such that it is expected to decrease peptide activity on K(v) channels. Unexpectedly, ACoTX1 exhibited an activity similar to that of CoTX1 towards SKCa channels, while it was markedly more potent on IKCa1 and several voltage-gated K+ channels.

Amino Acid Sequence↗
PubMed2004

BmTx3, a scorpion toxin with two putative functional faces separately active on A-type K+ and HERG currents.

A novel HERG channel blocker was isolated from the venom of the scorpion Buthus martensi Karsch, sequenced and characterized at the pharmacological level after chemical synthesis. According to the determined amino acid sequence, the cDNA and genomic genes were then cloned. The genomic gene consists of two exons interrupted by an intron of 65 bp at position -6 upstream from the mature toxin. The protein sequence of this toxin was completely identical with that of a known A-type K+ current blocker BmTx3, belonging to scorpion alpha-KTx subfamily 15. Thus BmTx3 is the first reported alpha-KTx peptide also showing HERG-blocking activity, like gamma-KTx peptides. Moreover, different from classical alpha-KTx peptides, such as charybdotoxin, BmTx3 cannot block Shaker -type K+ channels. Phylogenetic tree analysis reveals that this toxin takes an intermediate position between classical alpha-KTx and gamma-KTx toxins. From a structural point of view, we propose that two separate functional faces might exist on the BmTx3 molecule, responsible for the two different K+-current-blocking functions. Face A, composed of Arg18 and Lys19 in the alpha-helix side, might correspond to HERG blocking activity, whereas Face B, containing a putative functional dyad (Lys27 and Tyr36) in the beta-sheet side, might correspond to A-type blocking activity. A specific deletion mutant with the disrupted Face B, BmTx3-Y36P37del, loses the A-type current-blocking activity, but keeps a similar HERG-blocking activity, as seen with the wild-type toxin.

Amino Acid Sequence↗
PubMed1996

A novel structural class of K+-channel blocking toxin from the scorpion Pandinus imperator.

A novel peptide was purified and characterized from the venom of the scorpion Pandinus imperator. Analysis of its primary structure reveals that it belongs to a new structural class of K+-channel blocking peptide, composed of only 35 amino acids, but cross-linked by four disulphide bridges. It is 40, 43 and 46% identical to noxiustoxin, margatoxin and toxin 1 of Centruroides limpidus respectively. However, it is less similar (26 to 37% identity) to toxins from scorpions of the geni Leiurus, Androctonus and Buthus. The disulphide pairing was determined by sequencing heterodimers produced by mild enzymic hydrolysis. They are formed between Cys-4-Cys-25, Cys-10-Cys-30, Cys-14-Cys-32 and Cys-20-Cys-35. Three-dimensional modelling, using the parameters determined for charybdotoxin, showed that is it possible to accommodate the four disulphide bridges in the same general structure of the other K+-channel blocking peptides. The new peptide (Pil) blocks Shaker B K+ channels reversibly. It also displaces the binding of a known K+-channel blocker, [125I]noxiustoxin, from rat brain synaptosomal membranes with an IC50 of about 10 nM.

Amino Acid Sequence↗
PubMed1998

Cobatoxins 1 and 2 from Centruroides noxius Hoffmann constitute a subfamily of potassium-channel-blocking scorpion toxins.

Potassium-channel-blocking scorpion toxins (alpha-K-toxins) have been shown to be valuable tools for the study of potassium channels. Here we report two toxins, cobatoxin 1 and 2, of 32 amino acids, containing three disulphide bridges, that were isolated from the venom of the Mexican scorpion Centruroides noxius. Their primary sequences show less than 40% identity to other alpha-K-toxins. It is therefore proposed that they belong to subfamily 9. The cDNA of cobatoxin 1 encodes a putative signal peptide, a putative short propeptide, the mature peptide and two amino acids that are processed to leave cobatoxin 1 amidated at the C-terminus. In rat brain synaptosomal membranes cobatoxin 1 and cobatoxin 2 bind to a common binding site of alpha-K-toxins with Ki values of 109 pM and 87 pM, respectively. Moreover, they block the Shaker and Kv1.1 K+ channels with moderate affinities, with Kd values of around 0.7 microM and 4.1 microM (Shaker) and 0.5 microM and 1.0 microM (Kv1.1), respectively. A three-dimensional model of cobatoxin 1 was generated and used to interpret the obtained functional data on a structural basis.

Amino Acid Sequence↗
PubMed2000

Chemical synthesis and characterization of Pi1, a scorpion toxin from Pandinus imperator active on K+ channels.

Pi1 is a 35-residue toxin cross-linked by four disulfide bridges that has been isolated from the venom of the chactidae scorpion Pandinus imperator. Due to its very low abundance in the venom, we have chemically synthesized this toxin in order to study its biological activity. Enzyme-based proteolytic cleavage of the synthetic Pi1 (sPi1) demonstrates half-cystine pairings between Cys4-Cys25, Cys10-Cys30, Cys14-Cys32 and Cys20-Cys35, which is in agreement with the disulfide bridge organization initially reported on the natural toxin. In vivo, intracerebroventricular injection of sPi1 in mice produces lethal effects with an LD50 of 0.2 microgram per mouse. In vitro, the application of sPi1 induces drastic inhibition of Shaker B (IC50 of 23 nM) and rat Kv1.2 channels (IC50 of 0.44 nM) heterologously expressed in Xenopus laevis oocytes. No effect was observed on rat Kv1.1 and Kv1.3 currents upon synthetic peptide application. Also, sPi1 is able to compete with 125I-labeled apamin for binding onto rat brain synaptosomes with an IC50 of 55 pM. Overall, these results demonstrate that sPi1 displays a large spectrum of activities by blocking both SK- and Kv1-types of K+ channels; a selectivity reminiscent of that of maurotoxin, another structurally related four disulfide-bridged scorpion toxin that exhibits a different half-cystine pairing pattern.

Amino Acid Sequence↗
PubMed2002

Differential sensitivity of sodium channels from the central and peripheral nervous system to the scorpion toxins Lqh-2 and Lqh-3.

The scorpion alpha-toxins Lqh-2 and Lqh-3, isolated from the venom of the Israeli yellow scorpion Leiurus quinquestriatus hebraeus, were previously shown to be very potent in removing fast inactivation of rat skeletal muscle sodium channels (Chen et al., 2000). Here, we show that tetrodotoxin-sensitive neuronal channels NaV1.2 and NaV1.7, which are mainly expressed in mammalian central and peripheral nervous systems, respectively, are differentially sensitive to these two toxins. rNaV1.2 and hNaV1.7 channels were studied with patch-clamp methods upon expression in mammalian cells. While Lqh-3 was about 100-times more potent in removing inactivation in hNaV1.7 channels compared with rNaV1.2, Lqh-2 was about 20-times more active in the other direction. Site-directed mutagenesis showed that the differences in the putative binding sites for these toxins, the S3-4 linkers of domain 4, are of major importance for Lqh-3, but not for Lqh-2.

Animals↗
PubMed1980

Covalent labeling of protein components of the sodium channel with a photoactivable derivative of scorpion toxin.

Azidonitrobenzoyl mono[125I]iodo scorpion toxin can be covalently attached to its receptor site in electrically excitable neuroblastoma cells or synaptosomes by photolysis. A polypeptide of Mr approximately 250,000 is specifically labeled in neuroblastoma cells. Labeling is blocked by unlabeled scorpion toxin and by depolarization. This polypeptide is not labeled in a variant neuroblastoma clone lacking voltage-sensitive sodium channels. Polypeptides of Mr approximately 250,000 and Mr approximately 32,000 are specifically labeled in synaptosomes. This labeling is also blocked by unlabeled toxin and by depolarization. These results identify specific polypeptides of Mr approximately 250,000 and Mr approximately 32,000 that are components of the sodium channel.

Affinity Labels↗
PubMed1981

Na+-channel-associated scorpion toxin receptor sites as probes for neuronal evolution in vivo and in vitro.

Purified neurotoxin II of the scorpion Androctonus australis Hector (ScTx) has previously been shown to bind specifically to the Na+-ionophore-associated, voltage-sensitive receptor sites of excitable cells. We have conducted binding studies, using high-specific-activity 125I-labeled ScTx, to detect and quantify the Na+-channel receptors on cells of the developing fetal mouse brain. In vivo, the onset of detectable specific binding is at 12 fetal days. The rate of receptor appearance is initially slow but increases sharply as of the 16th day of mouse ontogenesis. The mean number of receptors at 12 and 19 days is 120 and 20,000 per cell, respectively (i.e., 0.5 and 80 per square micrometer). When corrected for the fraction of cell population corresponding to putative neuroblasts and neurons, identified by immunofluorescence as tetanus toxin binding cells, these values are, respectively, 1040 and 33,900 ScTx receptors per tetanus toxin binding cell or 4.2 and 136 per square micrometer. At all stages, the toxin binds to a single class of noninteracting sites; Kd = 0.1-0.5 nM. Similar findings in terms of ScTx-receptor properties and quantitative evolution were obtained in vitro. Specific 125I-labeled ScTx binding the presence of tetanus toxin binding cells. In cultures of central nervous system glia without neurons, only nonspecific low-level ScTx binding was detected. These results suggest that the high-affinity scorpion toxin receptors may be used as quantitative markers of neuronal differentiation.

Animals↗
PubMed1988

Site of covalent attachment of alpha-scorpion toxin derivatives in domain I of the sodium channel alpha subunit.

Purified and reconstituted sodium channels from rat brain have been photoaffinity labeled with a photoactivable derivative of the alpha-scorpion toxin V from Leiurus quinquestriatus (LqTx). A battery of sequence-specific antibodies has been used to determine which of the peptides produced by chemical and enzymatic cleavage of the photolabeled sodium-channel alpha subunit contain covalently attached LqTx. Nearly all of the covalently attached LqTx is found within homologous domain I. Two site-directed antisera, which recognize residues 317 to 335 and residues 382 to 400, respectively, specifically immunoprecipitate a 14-kDa peptide produced by CNBr digestion to which LqTx is covalently attached. It is proposed that a portion of the receptor site for alpha-scorpion toxins is formed by peptide segment(s) between amino acid residues 335 and 378 which is located in an extracellular loop between transmembrane helices S5 and S6 of homologous domain I of the sodium channel alpha subunit.

Amino Acid Sequence↗
PubMed1989

Localization of the receptor site for alpha-scorpion toxins by antibody mapping: implications for sodium channel topology.

Site-directed and monoclonal antibodies recognizing different extracellular regions of the RII sodium channel alpha subunit have been used to determine the sequences that comprise the receptor for alpha-scorpion toxins by evaluating the effect of antibody on voltage-dependent binding of radio-labeled toxin isolated from Leiurus quinquestriatus to both reconstituted rat brain sodium channel and rat brain synaptosomes. Of six antibodies tested, two recognizing amino acid residues 355-371 and 382-400 located on an extracellular loop between transmembrane segments S5 and S6 of domain I and one recognizing residues 1686-1703 of a similar loop of domain IV inhibit binding by 30-55%. Inhibition is concentration-(EC50 = 0.4-2 microM) and time- (t1/2 = 40-80 min) dependent. Five different monoclonal antibodies recognizing the same extracellular loop in domain I inhibit binding completely with similar EC50 values as observed for site-directed antibodies. Kinetic studies of the antibody effect are consistent with a slowly reversible competition for the toxin receptor site. Our results suggest that the extracellular loops between segments S5 and S6 of domains I and IV comprise at least part of the alpha-scorpion toxin receptor site and support the membrane topology models in which domains I and IV are adjacent in the tertiary structure of the channel protein and six transmembrane sequences are contained in each of the four homologous domains.

Animals↗
PubMed2002

kappa-Hefutoxin1, a novel toxin from the scorpion Heterometrus fulvipes with unique structure and function. Importance of the functional diad in potassium channel selectivity.

An important and exciting challenge in the postgenomic era is to understand the functions of newly discovered proteins based on their structures. The main thrust is to find the common structural motifs that contribute to specific functions. Using this premise, here we report the purification, solution NMR, and functional characterization of a novel class of weak potassium channel toxins from the venom of the scorpion Heterometrus fulvipes. These toxins, kappa-hefutoxin1 and kappa-hefutoxin2, exhibit no homology to any known toxins. NMR studies indicate that kappa-hefutoxin1 adopts a unique three-dimensional fold of two parallel helices linked by two disulfide bridges without any beta-sheets. Based on the presence of the functional diad (Tyr(5)/Lys(19)) at a distance (6.0 +/- 1.0 A) comparable with other potassium channel toxins, we hypothesized its function as a potassium channel toxin. kappa-Hefutoxin 1 not only blocks the voltage-gated K(+)-channels, Kv1.3 and Kv1.2, but also slows the activation kinetics of Kv1.3 currents, a novel feature of kappa-hefutoxin 1, unlike other scorpion toxins, which are considered solely pore blockers. Alanine mutants (Y5A, K19A, and Y5A/K19A) failed to block the channels, indicating the importance of the functional diad.

Amino Acid Sequence↗
PubMed2003

Dissection of the functional surface of an anti-insect excitatory toxin illuminates a putative "hot spot" common to all scorpion beta-toxins affecting Na+ channels.

Scorpion beta-toxins affect the activation of voltage-sensitive sodium channels (NaChs). Although these toxins have been instrumental in the study of channel gating and architecture, little is known about their active sites. By using an efficient system for the production of recombinant toxins, we analyzed by point mutagenesis the entire surface of the beta-toxin, Bj-xtrIT, an anti-insect selective excitatory toxin from the scorpion Buthotus judaicus. Each toxin mutant was purified and analyzed using toxicity and binding assays, as well as by circular dichroism spectroscopy to discern the differences among mutations that caused structural changes and those that specifically affected bioactivity. This analysis highlighted a functional discontinuous surface of 1405 A(2), which was composed of a number of non-polar and three charged amino acids clustered around the main alpha-helical motif and the C-tail. Among the charged residues, Glu(30) is a center of a putative "hot spot" in the toxin-receptor binding-interface and is shielded from bulk solvent by a hydrophobic "gasket" (Tyr(26) and Val(34)). Comparison of the Bj-xtrIT structure with that of other beta-toxins that are active on mammals suggests that the hot spot and an adjacent non-polar region are spatially conserved. These results highlight for the first time structural elements that constitute a putative "pharmacophore" involved in the interaction of beta-toxins with receptor site-4 on NaChs. Furthermore, the unique structure of the C-terminal region most likely determines the specificity of excitatory toxins for insect NaChs.

Amino Acid Sequence↗
PubMed2005

Transduction of the scorpion toxin maurocalcine into cells. Evidence that the toxin crosses the plasma membrane.

Maurocalcine (MCa) is a 33-amino-acid residue peptide toxin isolated from the scorpion Scorpio maurus palmatus. External application of MCa to cultured myotubes is known to produce Ca2+ release from intracellular stores. MCa binds directly to the skeletal muscle isoform of the ryanodine receptor, an intracellular channel target of the endoplasmic reticulum, and induces long lasting channel openings in a mode of smaller conductance. Here we investigated the way MCa proceeds to cross biological membranes to reach its target. A biotinylated derivative of MCa was produced (MCa(b)) and complexed with a fluorescent indicator (streptavidine-cyanine 3) to follow the cell penetration of the toxin. The toxin complex efficiently penetrated into various cell types without requiring metabolic energy (low temperature) or implicating an endocytosis mechanism. MCa appeared to share the same features as the so-called cell-penetrating peptides. Our results provide evidence that MCa has the ability to act as a molecular carrier and to cross cell membranes in a rapid manner (1-2 min), making this toxin the first demonstrated example of a scorpion toxin that translocates into cells.

Amino Acid Sequence↗
PubMed1985

Electron microscopic and optical diffraction analysis of the structure of scorpion muscle thick filaments.

We rapidly and gently isolated thick filaments from scorpion tail muscle by a modification of the technique previously described for isolating Limulus thick filaments. Images of negatively stained filaments appeared to be highly periodic, with a well-preserved myosin cross-bridge array. Optical diffraction patterns of the electron micrograph images were detailed and similar to optical diffraction patterns from Limulus and tarantula thick filaments. Analysis of the optical diffraction patterns and computed Fourier transforms, together with the appearance of the filaments in the micrographs, suggested a model for the filaments in which the myosin cross-bridges were arranged on four helical strands with 12 cross-bridges per turn of each strand, thus giving the observed repeat every third cross-bridge level. Comparison of the scorpion thick filaments with those isolated from the closely related chelicerate arthropods, Limulus and tarantula, revealed that they were remarkably similar in appearance and helical symmetry but different in diameter.

Animals↗