Small conductance calcium-activated K+ channels, SkCa, but not voltage-gated K+ (Kv) channels, are implicated in the antinociception induced by CGS21680, a A2A adenosine receptor agonist

It has been shown that A2A adenosine receptors are implicated in pain modulation. The precise mechanism by which activation of A2A receptors produces analgesic effects, however, remains unclear. The aim of this study was to investigate the possible involvement of apamin-sensitive calcium-activated potassium channels (SKCa) and voltage-gated potassium (Kv) channels in A2A receptor activation-induced analgesic effects. Using mice, we evaluated the influence of apamin, a non specific blocker of SKCa channels, Lei-Dab7 (an analog of scorpion Leiurotoxin), a selective blocker of SKCa2 channels, and kaliotoxin (KTX) a Kv channel blocker, on the CGS 21680 (A2A adenosine receptor agonist)-induced increases in hot plate and tail pinch latencies. All drugs were injected in mice via the intracerebroventricular route. We found that apamin and Lei-Dab7, but not KTX, reduced antinociception produced by CGS21680 on the hot plate and tail pinch tests in a dose dependent manner. Lei-Dab 7 was more potent than apamin in this regard. We conclude that SKCa but not Kv channels are implicated in CGS 21680-induced antinociception.

Quantitative variability in the biodistribution and in toxinokinetic studies of the three main alpha toxins from the Androctonus australis hector scorpion venom

Scorpion stings represent a medical problem in numerous countries. The scorpion Androctonus australis hector produces three alpha toxins (Aah I to III), which are responsible for most of the lethality in mammals. These toxins act on sodium channel and do not cross-react immunologically. We used RIA and ELISA to measure the concentrations of these three toxins in plasma, urine and different organs after i.v. and s.c. injections of water extracts of venoms in rabbits or mice. In both animals, the toxins rapidly appeared in plasma after s.c. injection as it was previously described for the whole venom. However, the toxins disappeared from the blood more quickly than did other main components of the venom. Thus, serotherapy must be initiated immediately to prevent the toxin from reaching its target. We also detected the toxins in urine, kidneys, heart and lungs, but not in the brain. However, the concentration of Aah II was always lower than that of Aah I. Analysis of five samples of venom collected in different areas of southern Tunisia showed that a large polymorphism exists for the three toxins. This is yet another difficulty for serotherapy as there is no cross-antigenicity between them.

Engineering of a recombinant Fab from a neutralizing IgG directed against scorpion neurotoxin AahI, and functional evaluation versus other antibody fragments

Antibody-based therapy is the only specific treatment for scorpion envenomation. However, there are still major drawbacks associated with its use; mainly because antivenoms are still prepared from immune equine serum raised against crude venoms, whereas only a limited number of neurotoxins are responsible for the lethality of the venom. Using a murine hybridoma that secretes a well-characterized neutralizing IgG directed to neurotoxins AahI and AahIII from the venom of the scorpion Androctonus australis, we constructed a recombinant Fab (rFab) fragment, which was produced and purified from transformed bacteria. It recognized toxin AahI with a high affinity (KD = 8.2 x 10(-11)) equivalent to the homologous pFab prepared by papain digestion of whole IgG. Although the AahI-neutralizing capacity of protein L-purified rFab was low compared to other recombinant antibody formats (scFv and diabody) investigated in parallel, the antibody engineering approach presented here provides an innovative way to synthesize novel toxin-neutralizing molecules. It may serve as a strategy for designing a new generation of antivenoms.

First chemical synthesis of a scorpion α-toxin affecting sodium channels: The Aah I toxin ofAndroctonus australis hector

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.

Molecular cloning and functional expression of the alpha-scorpion toxin BotIII: pivotal role of the C-terminal region for its interaction with voltage-dependent sodium channels

Alpha scorpion toxins bind to receptor site 3 on voltage-dependent sodium channels and inhibit their inactivation. The alpha-scorpion toxin BotIII is the most toxic protein of Buthus occitanus tunetanus. Its sequence differs only by three amino acid residues from that of AahII, the most active alpha-toxin. Due to their high affinity and selectivity for mammalian sodium channels, BotIII and AahII represent powerful tools for studying the molecular determinants of specificity for voltage-dependent sodium channels. Sequence analysis of BotIII gene has revealed two exons separated by a 381-bp intron and a signal peptide of 19 amino acids. We succeeded in expressing BotIII in significantly higher amounts than AahII the only expressed strict alpha anti-mammalian scorpion toxin reported in the literature. We have also modified specific amino acid residues of BotIII. The recombinant and the natural toxins differ by the amidation of the C-terminal residue. Toxicity and binding experiments indicated: (a) the affinity of rBotIII-OH and rAahII-OH (rBotIII-OH with the 3 mutations R10V, V51L, N64H) for the voltage-dependent sodium channels is reduced compared to the natural toxins. This data revealed the important role of the C-terminal amidation for the biological activity of BotIII and AahII; (b) the single mutation N64H is responsible for the difference of toxicity and affinity between rBotIII-OH and rAahII-OH; (c) the addition of the sequence GR to rBotIII-OH leads to the loss of biological activity. This study is in agreement with the important role attributed to the C-terminal sequence of alpha-toxins in their interaction with sodium channels receptors.

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.

PnTx4-3, a new insect toxin from Phoneutria nigriventer venom elicits the glutamate uptake inhibition exhibited by PhTx4 toxic fraction

Several pools of neurotoxic peptides obtained from fractionated Phoneutria nigriventer venom induce different toxicological effects. One of them, PhTx4, is highly toxic towards insects and displays only a slight toxicity when injected in mice. Also, this fraction contains a class of peptides that are able to inhibit glutamate uptake in preparations of mammalian central nervous systems (CNS). In this work a new toxin called PnTx4-3 was isolated from the PhTx4 fraction by reverse phase and anion exchange steps using high performance liquid chromatography (HPLC). Edman sequencing of PnTx4-3 revealed that it was a polypeptide of 48 amino acid residues, containing 10 cysteines cross-linked by five disulfide bridges. The molecular mass measured by ES-Q-TOF mass spectrometry was 5199.49+/-0.64 Da, which is very close to the calculated mass from amino acid sequence (5199.99 Da). This toxin induces immediate excitatory effects when injected intrathoracically in house flies and cockroaches. Intracerebroventricular injections of 30 microg of PnTx4-3 in mice resulted in no apparent signs of intoxication. In order to make an orthologous comparison, pharmacological characterisation were carried out in rat brain synaptosomes by using [3H]-L-glutamate, showed that the whole PhTx4 fraction as well as the pure toxins PnTx4-3, Tx4(6-1) and Tx4(5-5) obtained of this fraction, were able to inhibit the glutamate uptake in the micromolar concentration range. PnTx4-3 inhibits the glutamate uptake in a dose dependent manner, with an IC50 of approximately 1 microM. PnTx4-3 is highly homologous to the Tx4(6-1) and Tx4(5-5) toxins previously described from the same fraction.

Critical amino acid residues determine the binding affinity and the Ca2+ release efficacy of maurocalcine in skeletal muscle cells

Maurocalcine (MCa) is a 33 amino acid residue peptide toxin isolated from the scorpion Scorpio maurus palmatus. MCa and mutated analogues were chemically synthesized, and their interaction with the skeletal muscle ryanodine receptor (RyR1) was studied on purified RyR1, sarcoplasmic reticulum (SR) vesicles, and cultured myotubes. MCa strongly potentiates [3H]ryanodine binding on SR vesicles (7-fold at pCa 5) with an apparent EC50 of 12 nm. MCa decreases the sensitivity of [3H]ryanodine binding to inhibitory high Ca2+ concentrations and increases it to the stimulatory low Ca2+ concentrations. In the presence of MCa, purified RyR1 channels show long-lasting openings characterized by a conductance equivalent to 60% of the full conductance. This effect correlates with a global increase in Ca2+ efflux as demonstrated by MCa effects on Ca2+ release from SR vesicles. In addition, we show for the first time that external application of MCa to cultured myotubes produces a cytosolic Ca2+ increase due to Ca2+ release from 4-chloro-m-cresol-sensitive intracellular stores. Using various MCa mutants, we identified a critical role of Arg24 for MCa binding onto RyR1. All of the other MCa mutants are still able to modify [3H]ryanodine binding although with a decreased EC50 and a lower stimulation efficacy. All of the active mutants produce both the appearance of a subconductance state and Ca2+ release from SR vesicles. Overall, these data identify some amino acid residues of MCa that support the effect of this toxin on ryanodine binding, RyR1 biophysical properties, and Ca2+ release from SR.

Solution structure of Pi4, a short four-disulfide-bridged scorpion toxin specific of potassium channels

Pi4 is a short toxin found at very low abundance in the venom of Pandinus imperator scorpions. It is a potent blocker of K(+) channels. Like the other members of the alpha-KTX6 subfamily to which it belongs, it is cross-linked by four disulfide bonds. The synthetic analog (sPi4) and the natural toxin (nPi4) have been obtained by solid-phase synthesis or from scorpion venom, respectively. Analysis of two-dimensional (1)H NMR spectra of nPi4 and sPi4 indicates that both peptides have the same structure. Moreover, electrophysiological recordings of the blocking of Shaker B K(+) channels by sPi4 (K(D) = 8.5 nM) indicate that sPi4 has the same blocking activity of nPi4 (K(D) = 8.0 nM), previously described. The disulfide bonds have been independently determined by NMR and structure calculations, and by Edman-degradation/mass-spectrometry identification of peptides obtained by proteolysis of nPi4. Both approaches indicate that the pairing of the half-cystines is (6)C-(27)C, (12)C-(32)C, (16)C-(34)C, and (22)C-(37)C. The structure of the toxin has been determined by using 705 constraints derived from NMR data on sPi4. The structure, which is well defined, shows the characteristic alpha/beta scaffold of scorpion toxins. It is compared to the structure of the other alpha-KTX6 subfamily members and, in particular, to the structure of maurotoxin, which shows a different pattern of disulfide bridges despite its high degree of sequence identity (76%) with Pi4. The structure of Pi4 and the high amounts of synthetic peptide available, will enable the detailed analysis of the interaction of Pi4 with K(+) channels.

Synthesis and characterization of Pi4, a scorpion toxin from Pandinus imperator that acts on K+ channels

Pi4 is a 38-residue toxin cross-linked by four disulfide bridges that has been isolated from the venom of the Chactidae scorpion Pandinus imperator. Together with maurotoxin, Pi1, Pi7 and HsTx1, Pi4 belongs to the alpha KTX6 subfamily of short four-disulfide-bridged scorpion toxins acting on K+ channels. Due to its very low abundance in venom, Pi4 was chemically synthesized in order to better characterize its pharmacology and structural properties. An enzyme-based cleavage of synthetic Pi4 (sPi4) indicated half-cystine pairings between Cys6-Cys27, Cys12-32, Cys16-34 and Cys22-37, which denotes a conventional pattern of scorpion toxin reticulation (Pi1/HsTx1 type). In vivo, sPi4 was lethal after intracerebroventricular injection to mice (LD50 of 0.2 microg per mouse). In vitro, addition of sPi4 onto Xenopus laevis oocytes heterologously expressing various voltage-gated K+ channel subtypes showed potent inhibition of currents from rat Kv1.2 (IC50 of 8 pm) and Shaker B (IC50 of 3 nm) channels, whereas no effect was observed on rat Kv1.1 and Kv1.3 channels. The sPi4 was also found to compete with 125I-labeled apamin for binding to small-conductance Ca(2+)-activated K+ (SK) channels from rat brain synaptosomes (IC50 value of 0.5 microm). sPi4 is a high affinity blocker of the Kv1.2 channel. The toxin was docked (BIGGER program) on the Kv channel using the solution structure of sPi4 and a molecular model of the Kv1.2 channel pore region. The model suggests a key role for residues Arg10, Arg19, Lys26 (dyad), Ile28, Lys30, Lys33 and Tyr35 (dyad) in the interaction and the associated blockage of the Kv1.2 channel.

A maurotoxin with constrained standard disulfide bridging: innovative strategy of chemical synthesis, pharmacology, and docking on K+ channels

Maurotoxin (MTX) is a 34-residue toxin that has been isolated initially from the venom of the scorpion Scorpio maurus palmatus. It presents a large number of pharmacological targets, including small conductance Ca2+-activated and voltage-gated K+ channels. Contrary to other toxins of the alpha-KTx6 family (Pi1, Pi4, Pi7, and HsTx1), MTX exhibits a unique disulfide bridge organization of the type C1-C5, C2-C6, C3-C4, and C7-C8 (instead of the conventional C1-C5, C2-C6, C3-C7, and C4-C8, herein referred to as Pi1-like) that does not prevent its folding along the classic alpha/beta scaffold of scorpion toxins. Here, we developed an innovative strategy of chemical peptide synthesis to produce an MTX variant (MTXPi1) with a conventional pattern of disulfide bridging without any alteration of the toxin chemical structure. This strategy was used solely to address the impact of half-cystine pairings on MTX structural properties and pharmacology. The data indicate that MTXPi1 displays some marked changes in affinities toward the target K+ channels. Computed docking analyses using molecular models of both MTXPi1 and the various voltage-gated K+ channel subtypes (Shaker B, Kv1.2, and Kv1.3) were found to correlate with MTXPi1 pharmacology. A functional map detailing the interaction between MTXPi1 and Shaker B channel was generated in line with docking experiments.

Design and evaluation of a diabody to improve protection against a potent scorpion neurotoxin

Diabodies are recombinant, dimeric, antibody-based molecules composed of two non-covalently associated single-chain antibody fragments that bind to an antigen in a divalent manner. In an attempt to develop more effective therapeutic molecules against scorpion venoms, we designed a diabody derived from monoclonal antibody 9C2, which neutralizes the toxicity of scorpion neurotoxin AahI in mammals. The recombinant diabody produced in the periplasm of Escherichia coli was purified to homogeneity in a single step by protein L-agarose affinity chromatography. It was functional, and possessed a high binding affinity to AahI (8 x 10(-11) M). The bivalence of the diabody was confirmed by size-exclusion chromatography, isoelectrofocussing and electron microscopic observations. Finally, the diabody showed high thermal stability in serum and demonstrated protective activity when injected intraperitoneally in mice experimentally envenomed with toxin AahI. In conclusion, the diabody format gives the 9C2 molecule advantageous properties that are particularly important for potential clinical applications in the treatment of envenomations.

BotIT6: a potent depressant insect toxin from Buthus occitanus tunetanus venom

A new depressant insect toxin Buthus occitanus tunetanus insect-toxin 6 (BotIT6) was purified by high-performance liquid chromatography from Buthus occitanus tunetanus (Bot) venom. BotIT6 is very active against Blatella germanica (LD50=10ng/100mg body mass) thus being one of the most potent anti-insect toxin so far characterised. When compared to other insect toxin sequences, BotIT6 present high similarities with depressant insect toxins with an additional arginine residue at the C-terminus and a methionine at position 27. The calculated net charge of BotIT6 is positive (+3) whereas it is negative for classical depressant toxins: this might be associated with its high toxicity. Voltage current clump studies show that BotIT6 is not a very potent depressant insect toxin despite its high toxicity in vivo. BotIT6 is able to fully inhibit the specific binding of 125I AaHIT and 125I-BotIT2 on Periplaneta americana synaptosomal membrane vesicles with high affinities. Despite its higher toxicity BotIT6 is a weaker competitor with 125I AaHIT and 125I BotIT2 as compared to the other beta toxins.Altogether, these results may suggest that BotIT6 probably defines a novel sub-group of depressant anti-insect toxins for which the receptor site can be overlapping, but not identical to that for classical depressant insect toxins.

A strategy for inducing an immune response against Androctonus australis scorpion venom toxin I in mice. Production of high-affinity monoclonal antibodies and their use in a sensitive two-site immunometric assay

Scorpion neurotoxins acting on ion channels share some structural features but differ in antigenic and immunogenic properties. They are highly structured peptides, 60-70 amino acids long. Monoclonal antibodies have been obtained for Androctonus australis hector scorpion venom neurotoxin II (AahII) and a nontoxic synthetic analog ((Abu)(8) AahII). In this study, no antibody response was elicited in mice of various strains injected with AahI, the other important toxin of the venom, in a native or an inactive ((Abu)(8) AahI) form. We found that AahI was only immunogenic in BALB/c or C57BL/6 mice if it was coupled to a carrier protein. The helper protein molecule could be BSA, KLH, or the nontoxic analog of AahII. We obtained a panel of high-affinity mAbs with these immunogens. Two of these mAbs, including the very high-affinity antibody 9C2 (K(D)=0.11x10(-11) M), were used to set up a two-site ELISA, sensitive enough for the quantification of AahI in the biological fluids of envenomed animals. The detection limit of the assay was 75 pg/ml.

[Theoretical and experimental bases for treatment of scorpion envenomations]

Improving the efficacy of envenomation treatment depends on what is known about active molecules present in venoms. Regarding scorpions, studies carried out mainly on the most poisonous species have shown that the toxicity and mortality were due to small proteins-toxins--able to interfere with the normal process of the ionic channels. In certain cases, using the mouse model, it has been shown that over 90% of mortality was due to toxins operating on the sodium channels implicated in the action potential of the excitable cells. Pharmacokinetic studies have shown the diversity of their mode of action implying an adaptation of the means and tools intended to neutralise them. The toxins active on the sodium channels represent a family of proteins from 60 to 65 amino acids linked by 4 disulphide bridges with a very strong antigenic polymorphism; this has certain implications in terms of paraspecificity of antivenoms. The problem is even more complicated when one considers the variation of toxin quantity from one animal to another of the same species. Another approach is to identify the most active and represented toxins in venoms for each antigenic group and to develop a means of neutralizing them. It would also be possible to define toxoids for use either in the production of the antivenoms or as immunological protection for individuals at risk. Lastly, where symptomatic treatment is concerned, certain drugs such as aspirin, quinine or dandrolene have been shown definitely to increase the value of the LD50 in the mouse.

Liposomal encapsulation enhances antiviral efficacy of SPC3 against human immunodeficiency virus type-1 infection in human lymphocytes

Because encapsulation of antiviral drugs in liposomes resulted generally in improved activity against retroviral replication in vivo, the antiviral effects of free-SPC3 and liposome-associated SPC3 were compared in cultured human lymphocytes infected with HIV-1. SPC3 was entrapped in various liposomal formulations, either different in size (mean diameter of 100 and 250 nm), SPC3 concentration or cholesterol content. Liposome-associated SPC3 were tested for both inhibition of cell-cell fusion and infection with HIV-1 clones. SPC3 inhibited HIV-1-induced fusion at a micromolar concentration range. When associated with liposomes, SPC3 was found to be about 10-fold more potent than free SPC3 in inhibiting syncytium formation. Continuous treatment with free SPC3 also inhibited virus production in a dose-dependent manner, with inhibition of HIV infection of C8166 T-cells or human peripheral blood lymphocytes (PBLs) at micromolar concentrations. Liposomal entrapment was found to increase the antiviral efficacy of SPC3 by more than 10- and 5-fold in C8166 and PBLs, respectively. These data suggest that the liposome approach may be used to improve SPC3 antiviral efficacy.

Synthesis, 3-D structure, and pharmacology of a reticulated chimeric peptide derived from maurotoxin and Tsk scorpion toxins

Maurotoxin (MTX) is a 34-mer scorpion toxin cross-linked by four disulfide bridges that acts on both Ca(2+)-activated (SK) and voltage-gated (Kv) K(+) channels. A 38-mer chimera of MTX, Tsk-MTX, has been synthesized by the solid-phase method. It encompasses residues from 1 to 6 of Tsk at N-terminal, and residues from 3 to 34 of MTX at C-terminal. As established by enzyme cleavage, Tsk-MTX displays half-cystine pairings of the type C1-C5, C2-C6, C3-C7 and C4-C8 which, contrary to MTX, correspond to a disulfide bridge pattern common to known scorpion toxins. The 3-D structure of Tsk-MTX, solved by (1)H NMR, demonstrates that it adopts the alpha/beta scaffold of scorpion toxins. In vivo, Tsk-MTX is lethal by intracerebroventricular injection in mice (LD(50) value of 0.2 microg/mouse). In vitro, Tsk-MTX is as potent as MTX, or Tsk, to interact with apamin-sensitive SK channels of rat brain synaptosomes (IC(50) value of 2.5 nM). It also blocks voltage-gated K(+) channels expressed in Xenopus oocytes, but is inactive on rat Kv1.3 contrary to MTX.

Evolution of maurotoxin conformation and blocking efficacy towards Shaker B channels during the course of folding and oxidation in vitro

Maurotoxin (MTX) is a 34-mer scorpion toxin cross-linked by four disulphide bridges that acts on various K(+) channels, including the voltage-gated Shaker B subtype. In the present study, we have investigated over 80 h: (1) the time-course of folding of synthetic MTX (sMTX) by CD analysis; (2) the kinetics of disulphide bridge formation by MS; and (3) the potency of MTX in blocking Shaker B currents during the combined process of its in vitro folding and oxidation. From the CD data, we show that stable secondary structures of sMTX evolve sequentially over time, with the appearance of the alpha-helix within 5 h, followed by the formation of the beta-sheet within 22 h. Using MS analysis, the sMTX intermediates were also found to appear sequentially from the least (one-disulphide-bridged sMTX) to the most oxidized species (native-like, four-disulphide-bridged sMTX). The time course of formation of secondary structures coincides mainly with the occurrence of one-disulphide-bridged sMTX for the alpha-helix and two- or three-disulphide-bridged sMTX for the beta-sheet. On-line electrophysiological recordings, which measure sMTX blocking efficacy on K(+) currents during its folding and oxidation, were performed on Shaker B channels expressed in Xenopus oocytes. Unexpectedly, the results demonstrate that sMTX is highly potent at the initial stage of oxidation, whereas its blocking activity can be transiently and dramatically reduced at later stages during the course of folding/oxidation before it reaches full bioactivity. These data suggest that formation of disulphide bridges can both physically stabilize and alter the bioactive three-dimensional structure of sMTX.

Chemical synthesis, molecular modeling, and antimicrobial activity of a novel bacteriocin, MMFII

A new antimicrobial peptide, referred to as MMFII, was purified to homogeneity from lactic acid bacteria Lactococcus lactis, which were isolated from Tunisian dairy product. The complete amino acid sequence of the peptide has been established by amino acid analysis, Edman sequencing, and mass spectrometry and verified by solid-phase chemical synthesis. MMFII is a single-chain 37-residue polypeptide containing a single intramolecular disulfide bond, i.e., TSYGNGVHCNKSKCWIDVSELETYKAGTVSNPKDILW. It shares ca. 35% sequence identity with Leucocin A, a class IIa bacteriocin. Modeling based on the 3-D of Leucocin A shows three beta strands located in the N-terminal region (Thr1-Tyr3, Val7-Asn10, Lys13-Ile16) and an alpha helical domain from Asp17 to Asn31. When plotted as an alpha-helical wheel, the central alpha-helix of MMFII does not exhibit an amphipathic helical structure. The synthetic MMFII (sMMFII), obtained by the solid-phase method, was shown to be indistinguishable from the natural peptide. sMMFII is active against Lactococcus cremoris and Listeria ivanovii bacteria, whereas no activity was detected for any of the synthetic N-terminal truncated MMFII analogs Cys9-Trp37, Trp15-Trp37, and Val18-Trp37.

A recombinant scFv/streptavidin-binding peptide fusion protein for the quantitative determination of the scorpion venom neurotoxin AahI

We created a construct encoding a peptide known to mimic the binding properties of biotin fused to the carboxy-terminus of a scFv fragment that binds a scorpion toxin (AahI). This fusion protein was produced in the periplasm of bacteria and purified to homogeneity by single-step affinity chromatography on streptavidin-agarose with a yield close to 1 mg/l. DNA sequencing, dot blot and mass spectrometric analyses demonstrated the integrity of the soluble immunoconjugate. Fusion to the streptavidin-binding peptide did not affect the ability of the scFv to recognize its antigen with a high affinity (Kd = 2.3 x 10(-10) M). Similarly, the streptavidin-binding property was not impaired in the fusion protein. Thus, the immunoconjugate was bifunctional and had a low molecular mass of 28 kDa. This enabled us to develop rapid and sensitive immunoassays for the specific detection of the toxin AahI accurately to 0.6 ng/ml, opening up new perspectives for the diagnosis of envenomations.

Parameters affecting in vitro oxidation/folding of maurotoxin, a four-disulphide-bridged scorpion toxin

Maurotoxin (MTX) is a 34-mer scorpion toxin cross-linked by four disulphide bridges that acts on various K(+) channel subtypes. MTX adopts a disulphide bridge organization of the type C1-C5, C2-C6, C3-C4 and C7-C8, and folds according to the common alpha/beta scaffold reported for other known scorpion toxins. Here we have investigated the process and kinetics of the in vitro oxidation/folding of reduced synthetic L-MTX (L-sMTX, where L-MTX contains only L-amino acid residues). During the oxidation/folding of reduced L-sMTX, the oxidation intermediates were blocked by iodoacetamide alkylation of free cysteine residues, and analysed by MS. The L-sMTX intermediates appeared sequentially over time from the least (intermediates with one disulphide bridge) to the most oxidized species (native-like, four-disulphide-bridged L-sMTX). The mathematical formulation of the diffusion-collision model being inadequate to accurately describe the kinetics of oxidation/folding of L-sMTX, we have formulated a derived mathematical description that better fits the experimental data. Using this mathematical description, we have compared for the first time the oxidation/folding of L-sMTX with that of D-sMTX, its stereoisomer that contains only D-amino acid residues. Several experimental parameters, likely to affect the oxidation/folding process, were studied further; these included temperature, pH, ionic strength, redox potential and concentration of reduced toxin. We also assessed the effects of some cellular enzymes, peptidylprolyl cis-trans isomerase (PPIase) and protein disulphide isomerase (PDI), on the folding pathways of reduced L-sMTX and D-sMTX. All the parameters tested affect the oxidative folding of sMTX, and the kinetics of this process were indistinguishable for L-sMTX and D-sMTX, except when stereospecific enzymes were used. The most efficient conditions were found to be: 50 mM Tris/HCl/1.4 mM EDTA, pH 7.5, supplemented by 0.5 mM PPIase and 50 units/ml PDI for 0.1 mM reduced compound. These data represent the first report of potent stereoselective effects of cellular enzymes on the oxidation/folding of a scorpion toxin.