Microwave-assisted synthesis of organically functionalized hexa-molybdovanadates

The microwave-assisted reaction of (TBA)₄[β-Mo₈O₂₄] and (TBA)₃[H₃V₁₀O₂₈] with pentaerythritol or tris(hydroxymethyl)aminomethane yields polyanions with the general formula (TBA)₂[V₃Mo₃O₁₆(O₃–R)] (R: C₅H₈OH – 1; R: C₄H₆NH₂ – 3). Post-synthetic esterification of 1 yields the acylated derivative 2, with all compounds being characterized in the solid and solution state.

High binding yet accelerated guest rotation within a cucurbit[7]uril complex. Toward paramagnetic gyroscopes and rolling nanomachines

The (15-oxo-3,7,11-triazadispiro[5.1.5.3]hexadec-7-yl)oxidanyl, a bis-spiropiperidinium nitroxide derived from TEMPONE, can be included in cucurbit[7]uril to form a strong (K(a)∼ 2 × 10(5) M(-1)) CB[7]@bPTO complex. EPR and MS spectra, DFT calculations, and unparalleled increased resistance (a factor of ∼10(3)) toward ascorbic acid reduction show evidence of deep inclusion of bPTO inside CB[7]. The unusual shape of the CB[7]@bPTO EPR spectrum can be explained by an anisotropic Brownian rotational diffusion, the global tumbling of the complex being slower than rotation of bPTO around its "long molecular axis" inside CB[7]. The CB[7] (stator) with the encapsulated bPTO (rotator) behaves as a supramolecular paramagnetic rotor with increased rotational speed of the rotator that has great potential for advanced nanoscale machines requiring wheels such as cucurbiturils with virtually no friction between the wheel and the axle for optimum wheel rotation (i.e. nanopulleys and nanocars).

Medium-throughput ESR detection of superoxide production in undetached adherent cells using cyclic nitrone spin traps

Spin trapping with cyclic nitrones coupled to electron spin resonance (ESR) is recognized as a specific method of detection of oxygen free radicals in biological systems, especially in culture cells. In this case, the detection is usually performed on cell suspensions, which is however unsuitable when adhesion influences free radical production. Here, we performed ESR detection of superoxide with four spin traps (5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide, DEPMPO; 5-diisopropoxyphosphoryl-5-methyl-1-pyrroline N-oxide, DIPPMPO; (4R*, 5R*)-5-(diisopropyloxyphosphoryl)-5-methyl-4-[({[2-(triphenylphosphonio)ethyl]carbamoyl}oxy)methyl]pyrroline N-oxide bromide, Mito-DIPPMPO; and 6-monodeoxy-6-mono-4-[(5-diisopropoxyphosphoryl-5-methyl-1-pyrroline-N-oxide)-ethylenecarbamoyl-(2,3-di-O-methyl) hexakis (2,3,6-tri-O-methyl)]-β-cyclodextrin, CD-DIPPMPO) directly on RAW 264.7 macrophages cultured on microscope coverslip glasses after phorbol 12-myristate 13-acetate (PMA) stimulation. Distinct ESR spectra were obtained with each spin trap using this method. CD-DIPPMPO, a recently published phosphorylated cyclic nitrone bearing a permethylated β-cyclodextrin moiety, was confirmed as the most specific spin trap of the superoxide radical, with exclusive detection of the superoxide adduct. ESR detection performed on cells attached to coverslips represents significant advances over other methods in terms of simplicity, speed, and measurement under near-physiological conditions. It thus opens the way for numerous applications, such as medium-throughput screening of antioxidants and reactive oxygen species (ROS)-modulating agents.

[Snake venom proteins related to "vascular endothelial growth factor": new tools for therapeutic angiogenesis]

The Vascular Endothelial Growth Factor "VEGF" plays a pivotal role in the stimulation of angiogenesis. The VEGF isoforms (A-D) and PlGF act in a coordinate fashion to develop the vascular network. Numerous proteins closely related in structure and function to VEGF-A have been reported and were grouped in the VEGF family. Some predators make use of VEGF-like molecules with devastating results for their prey. VEGF-E, investigated in 1994, is encoded by the parapoxvirus (Orf virus). VEGF-F is a common term designating molecules which were isolated from snake venom (also known as svVEGF). These proteins are disulphide-linked homodimers of 110 amino acids each and have a molecular weight of approximately 25 kDa. Their primary structures show approximately 50% identity to VEGF-A. However, unlike VEGF-A, they do not contain any N-linked glycosylation sites. They interact with heparin but have a different binding domain from that of VEGF-A. Among species, these svVEGFs vary extensively in amino acid sequences and in receptor-binding specificities towards endogenous VEGF receptors. Understanding the properties that determine the specificity of these interactions could improve our knowledge of the VEGF-receptor interactions. This knowledge is essential to the development of new drugs in angiogenesis. This knowledge is essential to the development of new drugs in angiogenesis.

Molecular cloning and nucleotide sequence analysis of encoded anti-insect toxin BotIT2 from the scorpion Buthus occitanus tunetanus venom

Numerous toxins from scorpion venoms are much more toxic to insects than to other animal classes, and possess high affinity to Na+ channels. Many of them active on insects were purified from the venom of Buthus occitanus tunetanus. Using amino acid sequences of BotIT2 and RACE-PCR amplification (Rapid amplification of cDNA ends) technique, we isolated, identified and sequenced the nucleotide sequence from the venom glands of the scorpion Buthus occitanus tunetanus. The cDNA encodes a precursor of an insect toxin of 60 amino acid residues. The deduced nucleotide sequence toxin was identical to the determined amino acid sequence of BotIT2. BotIT2 is more similar to the excitatory toxins in its mode of action and to the depressant toxins in its primary structure.

[In vivo and in vitro protection against lethal activity of Buthus occitanus tunetanus venom with a recombinant protein]

We report the use of recombinant scorpion toxin in the form of fusion protein as antigen for mice immunisation. The aim is to produce protective antisera against lethal activity of the venom from Tunisian scorpion Buthus occitanus tunetanus, responsible for several annually reported human cases of scorpion stings. The gene encoding Bot III (the most toxic alpha toxin of Buthus occitanus tunetanus) was fused to the sequence encoding synthetic ZZ domains of staphylococcal protein A. The construct ZZ-Bot III was expressed in the periplasm of E. coli as a fusion protein and purified by affinity chromatography. The recombinant fusion protein was characterized and used as antigen to generate antibodies in mice. The antibodies against the recombinant protein neutralize the toxic venom (10 LD50/ml) and also confer protection for immunized mice against antigenically related mammal toxins.

Synthesis and biochemical applications of a solid cyclic nitrone spin trap: a relatively superior trap for detecting superoxide anions and glutathiyl radicals

A novel cyclic nitrone spin trap, 5-tert-butoxycarbonyl 5-methyl-1-pyrroline N-oxide (BMPO) as a pure white solid has been synthesized for the first time. BMPO offers several advantages over the existing spin traps in the detection and characterization of thiyl radicals, hydroxyl radicals, and superoxide anions in biological systems. The corresponding BMPO adducts exhibit distinct and characteristic electron spin resonance (ESR) spectral patterns. Unlike the 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-derived superoxide adduct, the BMPO superoxide adduct does not non-enzymatically decompose to the BMPO hydroxyl adduct. This feature is clearly perceived as a definite advantage of BMPO in its biological applications. In addition, the ESR spectrum of the BMPO glutathionyl adduct (BMPO/*SG) does not fully overlap with the spectrum of its hydroxyl adduct. This spectral feature is again distinctly different from that of DMPO because the ESR spectral lines of DMPO glutathionyl and hydroxyl radical adducts largely overlap. Finally, the ESR spectra of BMPO-derived adducts exhibit a much higher signal-to-noise ratio in biological systems. These favorable chemical and spectroscopic features make BMPO ideal for the detection of superoxide anions, hydroxyl and thiyl radicals in biochemical oxidation and reduction.

Amino acid structure and characterization of a heterodimeric disintegrin from Vipera lebetina venom

A heterodimeric disintegrin designed as lebein was isolated from crude Vipera lebetina venom using gel filtration, anion and cation exchange chromatographies on FPLC. The amino acid sequence of each subunit determined by Edman degradation contains 64 residues with ten half-cystines and an RGD site at the C-terminal part of the molecule. The molecular mass of native lebein determined by mass spectrometry was found to be 14083.4 Da and those of alpha and beta subunits were 6992.05 and 7117.62, respectively. These value are in good agreement with those calculated from the sequences. This protein strongly inhibits ADP induced platelet aggregation on human platelet rich plasma with IC(50)=160 nM. Sequences of this protein subunits displayed significant sequence similarities with many other monomeric and dimeric disintegrins reported from snake venoms. We identified an amino acid residue (N) in the hairpin loop of both subunits (CNRARGDDMNDYC) which is different from all other reported motifs of disintegrins and this subtle difference may contribute to the distinct affinities and selectivities of this class of proteins.

Electron spin resonance spin-trapping detection of superoxide generated by neuronal nitric oxide synthase

NOS is a ubiquitous enzyme that has an oxygenase and reductase activity. NOS reduces electron acceptors, at the reductase domain, by a one-electron mechanism that is not inhibited by SOD. One example of this activity is the direct reduction of ferricytochrome c by nNOS. Redox cycling electron acceptors (EA in Scheme 1), such as lucigenin and NBT, are reduced by NOS to generate an intermediate radical (EAred). This radical can then be reoxidized to the parent compound by oxygen, and in the process generate superoxide. Consequently, both NBT and lucigenin will enhance NADPH-dependent superoxide generation in the presence of flavoprotein reductases such as NOS. The artificial generation of superoxide from lucigenin and NBT is a major pitfall in the use of these compounds as superoxide probes. We conclude that the use of ESR spin-trapping techniques, although not free of problems, is a viable technique for the detection and quantification of superoxide in systems containing nNOS.

Purification, characterization and molecular modelling of two toxin-like proteins from the Androctonus australis Hector venom

Two toxin-like proteins (AahTL1 and AahTL3) were purified from the venom of the scorpion Androctonus australis Hector (Aah). AahTL1 and AahTL3 are the first non toxic proteins cross-reacting with AahI toxins group which indicates that these proteins can be used as a model of vaccins. In order to study structure-function relationships, their complete amino-acid sequences (66 residues) were determined, by automated Edman degradation. They show more than 50% of similarity with both AahI and AahIII antimammal toxins. Three-dimensional structural models of AahTL1 and AahTL3 constructed by homology suggest that the two proteins are structurally similar to antimammal scorpion alpha-toxins specific to voltage dependent Na+ channels. The models showed also that amino-acid changes between potent Aah toxins and both AahTL1 and AahTL3 disrupt the electrostatic potential gradient at their surface preventing their interaction with the receptor, which may explain their non toxicity.

Amino acid sequence of VlF: identification in the C-terminal domain of residues common to non-hemorrhagic metalloproteinases from snake venoms

The complete amino acid sequence of a non-hemorrhagic fibrino(geno)lytic enzyme (VlF) isolated from Vipera lebetina venom has been determined. VlF was subjected to separate enzymatic and chemical digestions. Resulting fragments were purified by RP-HPLC and subjected for sequencing by automated Edman degradation. The amino terminus of VlF was determined by mass spectrometry. VlF was shown to be composed of 202 residues having a relative molecular mass of 22,826 Da and containing a zinc-binding site and a catalytically active residue. It displayed significant sequence similarities with many other mature metalloproteinases reported from snake venoms. Sequence comparison of hemorrhagic and non-hemorrhagic mature metalloproteinases revealed the presence at the C-terminal part of the enzymes of two residues common to only hemorrhagic metalloproteinases and two others shared by only non-hemorrhagic ones.

Detection of superoxide anion using an isotopically labeled nitrone spin trap: potential biological applications

We describe the synthesis and biological applications of a novel nitrogen-15-labeled nitrone spin trap, 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide ([(15)N]EMPO) for detecting superoxide anion. Superoxide anion generated in xanthine/xanthine oxidase (100 nM min(-1)) and NADPH/calcium-calmodulin/nitric oxide synthase systems was readily detected using EMPO, a nitrone analog of 5,5'-dimethyl-1-pyrroline N-oxide (DMPO). Unlike DMPO-superoxide adduct (DMPO-OOH), the superoxide adduct of EMPO (EMPO-OOH) does not spontaneously decay to the corresponding hydroxyl adduct, making spectral interpretation less confounding. Although the superoxide adduct of 5-(diethoxyphosphoryl)-5-methyl-pyrroline N-oxide is more persistent than EMPO-OOH, the electron spin resonance spectra of [(14)N]EMPO-OOH and [(15)N]EMPO-OOH are less complex and easier to interpret. Potential uses of [(15)N]EMPO in elucidating the mechanism of superoxide formation from nitric oxide synthases, and in ischemia/reperfusion injury are discussed.

Purification and characterization of a growth factor-like which increases capillary permeability from Vipera lebetina venom

We have investigated the effect of Vipera lebetina venom on capillary permeability and isolated an increasing capillary permeability protein (ICPP) which is devoid of arginine ester hydrolase and phospholipase A2 activities. This protein was purified with a yield of about 0.2% by fast protein liquid chromatography (FPLC) using successively Superose 12, Mono Q, and Mono S columns and by high-pressure liquid chromatography (HPLC) on a C8 reverse-phase column. The purified protein migrated on SDS-PAGE as a band of about 27 kDa under nonreducing conditions and as a band of about 16 kDa under reducing conditions. Chromatography on a C8 column of reduced and alkylated protein yielded a single peak suggesting that this protein is homodimeric. This protein was refractory to Edman degradation chemistry. We used successfully a chemical unblocking involving the incubation of the protein with HCl in anhydrous methanol. The N-terminal amino acid sequence clearly shows considerable similarity to that of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF).

Effect of redox-active drugs on superoxide generation from nitric oxide synthases: biological and toxicological implications

In this article, we address the mechanism of superoxide formation from constitutive nitric oxide synthases (NOS). Merits and drawbacks of the various superoxide detection assays are reviewed. One of the most viable techniques for measuring superoxide from NOS is electron spin resonance (ESR) spin-trapping using a novel phosphorylated spin trap. Implications of superoxide and peroxynitrite formation from NOS enzymes in cardiovascular and cerebrovascular disorders are discussed.

Tetrahydrobiopterin-dependent inhibition of superoxide generation from neuronal nitric oxide synthase

The binding of calcium/calmodulin stimulates electron transfer between the reductase and oxygenase domains of neuronal nitric oxide synthase (nNOS). Here, we demonstrate using electron spin resonance spin-trapping with 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide that pterin-free nNOS generates superoxide from the reductase and the oxygenase domain by a calcium/calmodulin-dependent mechanism. Tetrahydrobiopterin (BH(4)) diminishes the formation of superoxide by a mechanism that does not cause inhibition of NADPH consumption. In contrast, BH(4) analogs 7,8-dihydrobiopterin and sepiapterin do not affect superoxide yields. L-Arginine alone inhibits the generation of superoxide by nNOS but not by C331A-nNOS mutant that has a low affinity for L-arginine. A greater decrease in superoxide yields is observed when nNOS is preincubated with L-arginine. This effect is in accordance with the slow binding rates of L-arginine to NOS in the absence of BH(4). L-Arginine alone or in combination with BH(4) decreases the rates of NADPH consumption. The effect of L-arginine on superoxide yields, however, was less dramatic than that caused by BH(4) as much higher concentrations of L-arginine are necessary to attain the same inhibition. In combination, L-arginine and BH(4) inhibit the formation of superoxide generation and stimulate the formation of L-citrulline. We conclude that, in contrast to L-arginine, BH(4) does not inhibit the generation of superoxide by controlling electron transfer through the enzyme but by stimulating the formation of the heme-peroxo species.

Superoxide generation by endothelial nitric oxide synthase: the influence of cofactors

The mechanism of superoxide generation by endothelial nitric oxide synthase (eNOS) was investigated by the electron spin resonance spin-trapping technique using 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide. In the absence of calcium/calmodulin, eNOS produces low amounts of superoxide. Upon activating eNOS electron transfer reactions by calcium/calmodulin binding, superoxide formation is increased. Heme-iron ligands, cyanide, imidazole, and the phenyl(diazene)-derived radical inhibit superoxide generation. No inhibition is observed after addition of L-arginine, NG-hydroxy-L-arginine, L-thiocitrulline, and L-NG-monomethyl arginine to activated eNOS. These results demonstrate that superoxide is generated from the oxygenase domain by dissociation of the ferrous-dioxygen complex and that occupation of the L-arginine binding site does not inhibit this process. However, the concomitant addition of L-arginine and tetrahydrobiopterin (BH4) abolishes superoxide generation by eNOS. Under these conditions, L-citrulline production is close to maximal. Our data indicate that BH4 fully couples L-arginine oxidation to NADPH consumption and prevents dissociation of the ferrous-dioxygen complex. Under these conditions, eNOS does not generate superoxide. The presence of flavins, at concentrations commonly employed in NOS assay systems, enhances superoxide generation from the reductase domain. Our data indicate that modulation of BH4 concentration may regulate the ratio of superoxide to nitric oxide generated by eNOS.

Reexamination of the mechanism of hydroxyl radical adducts formed from the reaction between familial amyotrophic lateral sclerosis-associated Cu,Zn superoxide dismutase mutants and H2O2

Amyotrophic lateral sclerosis (ALS) involves the progressive degeneration of motor neurons in the spinal cord and motor cortex. Mutations to Cu,Zn superoxide dismutase (SOD) linked with familial ALS are reported to increase hydroxyl radical adduct formation from hydrogen peroxide as measured by spin trapping with 5, 5'-dimethyl-1-pyrrolline N-oxide (DMPO). In the present study, we have used oxygen-17-enriched water and H2O2 to reinvestigate the mechanism of DMPO/.OH formation from the SOD and SOD mutants. The relative ratios of DMPO/.17OH and DMPO/.16OH formed in the Fenton reaction were 90% and 10%, respectively, reflecting the ratios of H217O2 to H216O2. The reaction of the WT SOD with H217O2 in bicarbonate/CO2 buffer yielded 63% DMPO/.17OH and 37% DMPO/.16OH. Similar results were obtained from the reaction between familial ALS SOD mutants and H217O2: DMPO/.17OH (64%); DMPO/.16OH (36%) from A4V and DMPO/.17OH (62%); and DMPO/.16OH (38%) from G93A. These results were confirmed further by using 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide spin trap, a phosphorylated analog of DMPO. Contrary to earlier reports, the present results indicate that a significant fraction of DMPO/.OH formed during the reaction of SOD and familial ALS SOD mutants with H2O2 is derived from the incorporation of oxygen from water due to oxidation of DMPO to DMPO/.OH presumably via DMPO radical cation. No differences were detected between WT and mutant SODs, neither in the concentration of DMPO/.OH or DEPMPO/.OH formed nor in the relative incorporation of oxygen from H2O2 or water.

Spin-trapping of free radicals formed during the oxidation of glutathione by tetramethylammonium peroxynitrite

Glutathionyl radical (GS.) formed during the oxidation of glutathione by tetramethylammonium peroxynitrite ([NMe4][ONOO]) was spin-trapped with 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO). This radical reacted with ammonium formate to form the carbon dioxide anion radical (CO2-.). The superoxide anion formed during oxidation of GSH by peroxynitrite salt was trapped with DMPO and detected as the DMPO-hydroxyl adduct. Addition of SOD mimic completely abolished the spectrum of the hydroxyl adduct but not the spectrum of the DMPO-glutathionyl radical adduct. Addition of seleno-DL-cystine or its reduced form caused a dramatic inhibition in the formation of spin adducts, suggesting that seleno-DL-cysteine is a more effective scavenger of peroxynitrite. The oxygen uptake observed during oxidation of GSH by peroxynitrite salt was inhibited by spin traps. In the presence of catalase, approximately 50% of the oxygen consumed was restored, indicating stoichiometric conversion of O2 to H2O2 during oxidation of GSH by peroxynitrite salt. Results indicate that nitrite and glutathione disulfide are formed as the major products during oxidation of GSH by peroxynitrite.

Cerastotin, a serine protease from Cerastes cerastes venom, with platelet-aggregating and agglutinating properties

Cerastotin, a thrombin-like enzyme from the venom of the desert viper Cerastes cerastes, has been purified by gel filtration on Sephadex G-75 and two ion-exchange chromatographies on Mono S columns. It is a neutral glycoprotein (pI = 6.6), present as a single polypeptide chain of 40 kDa. Its N-terminal sequence shows strong similarity with those of other thrombin-like enzymes from snake venoms. Cerastotin possesses esterase and amidolytic activities measured with N(alpha)-tosyl-L-arginine methyl ester and the thrombin chromogenic substrate D-phenylalanyl-L-pipecolyl-L-arginine p-nitroanilide, respectively. The amidolytic activity is inhibited by phenylmethylsulfonyl fluoride, N(alpha)-tosyl-L-lysine chloromethane, N(alpha)-tosyl-L-phenylalanyl chloromethane, D-phenylalanyl-L-prolyl-L-arginyl chloromethane and benzamidine, suggesting that cerastotin is a serine protease. Cerastotin efficiently clots human plasma and cleaves preferentially the alpha chain of fibrinogen. Cerastotin did not induce aggregation of washed normal platelets, but did aggregate platelets in the presence of exogenous fibrinogen. A monoclonal antibody directed against glycoprotein (GPIb), which specifically inhibits induced agglutination by ristocetin also completely blocks platelet aggregation induced by cerastotin. However, another anti-GPIb monoclonal antibody, which specifically inhibits alpha-thrombin binding to GPIb, did not prevent this aggregation. Furthermore, platelets which were desensitised by alpha-thrombin still aggregate in the presence of cerastotin, but not alpha-thrombin. Similarly a monoclonal antibody, anti-GPIIb-IIIa, which blocks fibrinogen binding, did not inhibit cerastotin-induced platelet aggregation. This activity is abolished in the presence of 1 mM phenylmethylsulfonyl fluoride and/or 10 mM EDTA. Cerastotin also agglutinates formalin-fixed and washed platelets, only in the simultaneous presence of fibrinogen and of Von Willebrand factor.

Further characterization and thrombolytic activity in a rat model of a fibrinogenase from Vipera lebetina venom

Vipera lebetina fibrinogenase (VlF) was shown to render fibrinogen incoagulable and to solubilize fibrin. The fibrinogenolytic activity of this enzyme was found to be 33 mg fibrinogen/min/mg protein. The study of the specificity of this enzyme revealed that it has no effect on purified factor X, prothrombin and protein C and on the specific chromogenic substrates of their active form. Plasminogen was not activated by VlF but slightly degraded. We have also compared the effect of VlF and plasmin on fibrinogen and shown that these two enzymes have a different sites of cleavage. This enzyme inhibited human platelet aggregation on PRP initiated by ADP and collagen but was without effect on the aggregation of washed rabbit platelets using thrombin as agonist. Administration of VlF in rat did not show any necrosis or hemorrhage in treated rats organ's. We therefore, examined the thrombolytic activity of VlF in a rat model of venous thrombosis. Thrombus was produced in the posterior vena cava by injection of human fibrinogen and thrombin. Injection of 5 mg/Kg body weight showed an evident flow restoration after one hour and measurement of the fibrinogen level a decrease of about 30% after 3 hrs. VlF's action is not dependent on plasminogen activators and may act synergistically with them, thereby providing an intriguing potential clinical application for dissolution of blood clots.

Purification, structure and activity of three insect toxins from Buthus occitanus tunetanus venom

One contractive and two depressant toxins active on insect were purified by high-performance liquid chromatography from the venom of Buthus occitanus tunetanus (Bot). The two depressant toxins, BotIT4 and BotIT5, differ only at position 6 (Arg for Lys) and are equally toxic to insects (LD50 to Blatella germanica = 110 ng/100 mg body weight). They show a strong antigenic cross-reaction with a depressive toxin from Leiurus quinquestriatus quinquestriatus (LqqIT2). The two toxins are able to inhibit with high affinity (K0.5 between 2 and 3 nM) the specific binding of the radioiodinated excitatory insect toxin (125I-AaHIT) on its receptor site on Periplaneta americana synaptosomal membranes. These toxins depolarize the cockroach axon, irreversibly block the action potential, and slow down and very progressively block the transmembrane transient Na+ current. The contracturant toxin BotIT1 is highly toxic to B. germanica (LD50 = 60 ng/ 100 mg body weight) and barely toxic to mice (LD50 = 1 microgram/20 g body weight) when injected intracerebroventricularly. It does not compete with 125I-AaHIT for its receptor site on P. americana synaptosomal membranes. On cockroach axon, BotIT1 develops plateau potentials and slows down the inactivation mechanism of the Na+ channels. Thus, BotIT1 belongs to the group of alpha insect-selective toxins and shows a strong sequence identity (> 90%) with Lqh alpha IT and LqqIII, two insect alpha-toxins previously purified from the venom of L. q. hebraeus and L. q. quinquestriatus. respectively.

In vivo protection against Androctonus australis hector scorpion toxin and venom by immunization with a synthetic analog of toxin II

A synthetic peptide mimicking the North African scorpion Androctonus australis hector toxin II was designed and produced by chemical solid-phase synthesis. It contains the entire sequence of toxin II (64 amino acid residues), with each half-cystine being replaced by the isosteric residue a-aminobutyric acid, and was thus devoid of disulfide bridges. This construct was totally nontoxic in mice even if large amounts, equivalent to 1000 times the LD50 of the original toxin, were injected by the intracerebroventricular route. The synthetic peptide, either as a monomer or polymerized by means of glutaraldehyde, induced the production of antitoxin neutralizing antibodies in immunized mice and rabbits. After three injections with either the monomeric or polymerized synthetic peptide, the immunized mice were protected against several lethal doses of the corresponding native toxin or scorpion venom. Six months after immunization, the mice were completely protected against challenge with eight LD50 of the original toxin. The protection was better when the polymerized synthetic peptide was used. One month after the start of the immunization program, it showed a good correlation between antibody titer and protection. However, antibody titer decreased with time but protection remained high. This suggests that additional factors other than circulating antibodies play a role in protective activity.

A new scorpion venom toxin paralytic to insects that affects Na+ channel activation. Purification, structure, antigenicity and mode of action

A new toxin, BotIT2, with a unique mode of action on the isolated giant axon of the cockroach Periplaneta americana and DUM (dorsal unpaired median) neurons, has been purified from the venom of the scorpion Buthus occitanus tunetanus. Its structural, antigenic and pharmacological properties are compared to those of three other groups of neurotoxins found in Buthidae scorpion venoms. Like excitatory, depressant and alpha-type insect-selective neurotoxins, BotIT2 is toxic to insects, but shows the following common and distinctive characteristics. (a) As alpha-type toxins, BotIT2 lack strict selectivity to insects; they have measurable but low toxicity to mice. (b) As depressant toxins and unlike alpha-type toxins, BotIT2 is able to displace iodinated AaHIT from its binding sites in insect neuronal membranes. This indicates that the binding site for BotIT2 is identical, contiguous or in allosteric interaction with that of AaHIT and depressant toxins. (c) The BotIT2 amino acid sequence shows strong similarity to depressant toxins. However, unexpectedly, despite this high sequence similarity, BotIT2 shares moderate cross-antigenic reactivity with depressant toxins. (d) Voltage and current-clamp studies show that BotIT2 induces limited depolarization concomitantly with the development of depolarizing after potential, repetitive activity and later plateau potentials terminated by bursts. Under voltage-clamp conditions, BotIT2 specifically acts on Na+ channels by decreasing the peak Na+ current and by simultaneously inducing a new current with very slow activation/deactivation kinetics. The voltage dependence of this slow current is not significantly different from that of the control current. These observations indicate that BotIT2 chiefly modifies the kinetics of axonal and DUM neuronal membrane Na(+)-channel activation.

Detection of thiyl radical adducts formed during hydroxyl radical- and peroxynitrite-mediated oxidation of thiols--a high resolution ESR spin-trapping study at Q-band (35 GHz)

Thiyl radicals (RS.) formed during peroxynitrite- or hydroxyl radical-dependent oxidation of thiols, i.e., glutathione (GSH) and L-cysteine (CySH) were trapped with 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) and analyzed by X-band and Q-band electron spin resonance (ESR) spectroscopy. At X-band, the ESR parameters of DMPO-glutathionyl radical adduct (DMPO/.SG) and DMPO-hydroxyl radical adduct (DMPO/.OH) are nearly similar in aqueous solutions and as a result, except for the lowfield spectral line, the remaining spectral lines of DMPO/ .SG virtually over-lap with those of the DMPO/.OH adduct. In contrast, at Q-band, most of the spectral lines due to the DMPO/.SG were separated from the DMPO/ .OH. Inclusion of a superoxide dismutase (SOD) mimic completely abolished the formation of the DMPO/.OH adduct and not the DMPO/.SG adduct during ONOO(-)-mediated oxidation of GSH and DMPO. In the presence of formate, the DMPO/.SG spectrum was replaced by the DMPO/.CO2- spectrum which was monitored by Q-band ESR spectroscopy. Thus, spin-trapping at Q-band provides unambiguous proof for the glutathionyl radical-dependent oxidation of formate by peroxynitrite. High resolution Q-band ESR spectra of DMPO/.Scys were also obtained. Biological applications of the Q-band spin-trapping technique to detect thiyl radicals in cellular systems are discussed.

A recombinant insect-specific alpha-toxin of Buthus occitanus tunetanus scorpion confers protection against homologous mammal toxins

We have constructed a cDNA library from venom glands of the scorpion Buthus occitanus tunetanus and cloned a DNA sequence that encodes an alpha-toxin. This clone was efficiently expressed in Escherichia coli as a fusion protein with two Ig-binding (Z) domains of protein A from Staphylococcus aureus. After CNBr treatment of the fusion protein and HPLC purification, we obtained approximately 1 mg recombinant apha-toxin/l bacterial culture. The toxin, called Bot XIV, displays no toxicity towards mammals but is active towards insects as shown by its paralytic activity against Blatella germanica cockroach and by electrophysiological studies on Periplaneta americana cockroaches. The Bot XIV protein fused to two Z domains is highly immunogenic in mice and induces production of antisera that specifically recognize and neutralize highly toxic components that had been injected into mice. This fusion protein could be very useful for development of potent protective antisera against scorpion venoms.

Effect of superoxide dismutase mimics on radical adduct formation during the reaction between peroxynitrite and thiols--an ESR-spin trapping study

We have reexamined the formation and reactions of radicals formed from peroxynitrite (ONOO-)-mediated oxidation of glutathione (GSH), L-cysteine (Cys), N-acetyl-D,L-penicillamine (NAP), and sodium bisulfite (NaHSO3). Sulfur-centered and superoxide union radicals were trapped using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and the radical adducts were analyzed by electron spin resonance (ESR) spectroscopy. The following sulfur-centered radicals were detected: glutathionyl radical (GS') from GSH, L-cysteinyl radical ('Scys) from L-cysteine, N-acetyl-D,L-penicillamine thiyl radical ('SNAP) from NAP, and sulfite anion radical (SO3-.) from NaHSO3. Additionally the formation of the hydroxyl radical adduct of DMPO (DMPO/'OH) was observed. DMPO/'OH formation was totally inhibited by low-molecular-weight superoxide dismutase (SOD) mimics. This suggests that DMPO/'OH was formed from the decay of the superoxide radical adduct of DMPO. In the presence of SOD mimics, the DMPO-sulfur-centered adducts were more persistent, suggesting that O2-. is partially responsible for the instability of DMPO-thiyl adducts. Sulfur-centered radicals formed during oxidation of thiols and sulfite by peroxynitrite react with ammonium formate to form the carbon dioxide anion radical (CO2-.). We conclude that sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite arise from a hydroxyl-radical-independent mechanism. Biological implications of peroxynitrite-mediated oxidation of thiols as well as the use of SOD mimics in biological spin-trapping are discussed.

Characterization of sulfur-centered radical intermediates formed during the oxidation of thiols and sulfite by peroxynitrite. ESR-spin trapping and oxygen uptake studies

Using a novel phosphorylated spin trap, 5-diethoxy-phosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), an analog of the commonly used trap 5,5'-dimethyl-1-pyrroline N-oxide (DMPO), we have investigated the reactions of sulfur-centered radicals produced from the oxidation of thiols and sulfite by peroxynitrite. The predominant species trapped in all cases are the corresponding sulfur-centered radicals, i.e. glutathionyl radical (GS) from glutathione (GSH), N-acetyl-DL-penicillamine thiyl radical (S-NAP) from N-acetyl-DL-penicillamine (NAP) and sulfate anion radical (SO3-) from sulfite. These radicals consume molecular oxygen forming either peroxyl or superoxide anion radicals. GS, S-NAP, and (SO3-)-derived radicals react with ammonium formate to form the carbon dioxide anion radical (CO2-). Further support of spin adduct assignments and radical reactions are obtained from photolysis of S-nitrosoglutathione and S-nitroso-N-acetyl-DL-penicillamine. We conclude that the direct reaction of peroxynitrite with thiols and sulfate forms thiyl and sulfate anion radicals, respectively, by a hydroxyl radical-independent mechanism. Pathological implications of thiyl radical formation and subsequent oxyradical-mediated chain reactions are discussed. Oxygen activation by thiyl radicals formed during peroxynitrite-mediated oxidation of glutathione may limit the effectiveness of GSH against peroxynitrite-mediated toxicity in cellular systems.

Cerastocytin, a new thrombin-like platelet activator from the venom of the Tunisian viper Cerastes cerastes

Cerastocytin, a thrombin-like enzyme from the venom of the desert viper, Cerastes cerastes, has been purified to homogeneity by fast performance liquid chromatography (FPLC) on Mono-Q and Mono-S columns. It is a basic protein (isoelectric point higher than 9) made of a single polypeptide chain of 38 kDa. Its N-terminal polypeptide sequence shows strong similarities with other thrombin-like enzymes from snake venoms. Nanomolar concentrations of cerastocytin induce aggregation of blood platelets. This activity is inhibited by chlorpromazine, theophylline and mepacrine, as in the case of platelet aggregation stimulated by low doses of thrombin. Cerastocytin also possesses an amidolytic activity measured with the thrombin chromogenic substrate S-2238. The platelet aggregating activity and the amidolytic activity of cerastocytin were inhibited by PMSF, TPCK, TLCK and soybean trypsin inhibitors, suggesting that cerastocytin is a serine proteinase. On the other hand, both amidolytic activity and platelet aggregating activity of cerastocytin were unaffected by hirudin or by antithrombin III in the presence of heparin. High concentrations of cerastocytin (1-10 microM) also cleaved prothrombin and Factor X.

5-(Diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide: a new efficient phosphorylated nitrone for the in vitro and in vivo spin trapping of oxygen-centered radicals

5-(Diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO, 2), a new spin trap, has been synthesized via a two-step synthetic route, and its ability to spin trap oxy radicals in biological milieu has been addressed. The in vitro spin trapping of hydroxyl and superoxide radicals was investigated in a phosphate buffer 0.1 M, and the hyperfine coupling constants of the spin adducts were determined. The rates of spin trapping of hydroxyl and superoxide radicals with 2 were found to be close to those reported for 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, the DEPMPO-superoxide spin adduct was shown to be significantly more persistent (15 times at pH 7) than the DMPO--superoxide spin adduct. Using 2 as a spin trap, the production of superoxide has been clearly characterized during the reperfusion of ischemic isolated rat hearts.

Purification from Vipera lebetina (desert adder) venom of a protein that depletes human complement

A rapid and efficient procedure for purification from Vipera lebetina venom of a low molecular weight anticomplement protein is described. The procedure used gel filtration on Superose 12, followed by ion-exchange chromatography on a Mono Q column. The purified protein migrated on SDS-PAGE as a single band of about 25,000 Da under nonreducing conditions and as a band of 16,000 Da under reducing conditions. Its isoelectric point was estimated to be 7.6 +/- 0.1. The isolated Vipera lebetina protein was found to decrease the hemolytic activity in human serum measured by assays for classical pathway and alternative pathway activation. The loss of the complement activity could be ascribed, at least in part, to a proteolytic cleavage of the alpha chains of C3 and C4. This protein was also found to be without action on human blood coagulation and on purified fibrinogen and Factor B.

[Characteristics of the first penicillinase-producing strains of Neisseria gonorrhoeae isolated in Tunisia]

The first penicillinase-producing strain of Neisseria gonorrhoeae was recently isolated in Tunisia (1989). Betalactamase production was detected by the iodometric agar test. Minimal inhibitory concentrations (MICs) in agar medium were 128 micrograms/ml for penicillin, ampicillin and amoxycillin. With the amoxycillin-clavulanic acid combination, MIC fell to 0.25 microgram/ml. An Asian-type plasmid pattern was evidenced in this strain, with presence of the 2.6 Mdal cryptic plasmid and of a 4.5 Mdal plasmid.

Purification and characterization of a fibrinogenase from Vipera lebetina (desert adder) venom

A fibrinogenase from Vipera lebetina venom was isolated by gel filtration in a Superose 12 column prep grade HR 16/50 and by ion-exchange in a Mono Q HR 5/5 column. The purified enzyme, which was obtained with a yield of 8 mg from 60 mg of crude venom, is a glycoprotein having an isoelectric point of 5.9 +/- 0.1 and a mol. wt of 26,000 +/- 1000 as estimated by SDS-PAGE. The biochemical characterization of the enzyme revealed that it hydrolyzes readily the B beta chain of fibrinogen and the A alpha chain as well as fibrin and casein. Over a pH range from 4 to 11 the enzyme was not inactivated by a 20 min treatment at 90 degrees C. The isolated fibrinogenase is inhibited by ethylenediamine tetraacetic acid, dithiothreitol and L-cysteine but not by phenylmethylsulfonyl fluoride. On the other hand, it is activated by Ca2+ and Mg2+. Purified fibrinogenase up to a dose of 100 micrograms/mouse shows no toxicity and has no hemorrhagic activity.

[Identification of toxic components from the venom of Cerastes cerastes and Vipera lebetina vipers; purification of phospholipases]

Cerastes cerastes and Vipera lebetina venoms have been fractionated and the different components analysed by electrophoresis on polyacrylamid gels. Phospholipases A2 contained in these two venoms have been purified and their electrophoretic properties compared.

Histidine-rich domain of the knob protein of the human malaria parasite Plasmodium falciparum

Membranes of erythrocytes infected with the human malaria parasite Plasmodium falciparum develop protrusions called knobs. These structures are essential for the survival of the parasite in the host, and their induction requires the synthesis of the knob protein by the parasite. We describe the isolation of a cDNA clone encoding the amino-terminal half of the knob protein. A cDNA library was constructed from RNA prepared from ring stages of a P. falciparum isolate that has retained its ability to induce knobs (knob+ phenotype). A synthetic oligonucleotide probe encoding polyhistidine was used to isolate the cDNA clone, which encodes the amino-terminal half of a polypeptide with all the known attributes of the knob protein. The gene is not transcribed in variants that do not synthesize the knob protein and thereby cannot induce knobs (knob- phenotype). The apparent lack of transcription in knob- variants is due to different mechanisms: although the gene is present in one knob- isolate, it has been deleted in a cloned knob- variant. The primary structure of the polypeptide deduced from a partial sequence of the cDNA is distinctly different from other malarial histidine-rich polypeptides. The amino-terminal sequence shows the characteristic features of a signal peptide. This is followed by a histidine-rich domain and a subsequent region which contains one histidine. Peptide map analysis of the knob protein is consistent with the structural features deduced from the sequence analysis of the cDNA.

Mini-F encoded proteins: identification of a new 10.5 kilodalton species

The elements which ensure the maintenance of the F plasmid are located in its f5 EcoRI restriction fragment. This f5 fragment constitutes a mini-F plasmid showing the same stability and copy number control as the entire F plasmid. The proteins expressed in minicells by wild-type or mutated f5 fragments were analysed by pH gradient two-dimensional electrophoresis. We identified seven f5-encoded polypeptides and located their genes on the F map. Among them, H1, an acidic polypeptide of mol. wt. 10.5 K, had not been detected before. It is in fact the most abundant f5-encoded polypeptide identified so far. In addition, we showed that both 10.5-K and 12-K protein bands detected by SDS-polyacrylamide gel electrophoresis are, respectively, composed of two polypeptides, H1 and H2, G1 and G2, of different isoelectric points. Polypeptides H2 and G2, respectively, share common coding sequences with polypeptides H1 and G1. Their possible biological significance is discussed. The sequences coding for polypeptides H1/H2 and G1/G2 are clustered in a 800-bp long region located between the two mini-F origin sites and are proposed to be organized as an operon. The results reported in the accompanying paper point out the importance of polypeptides G1/G2 and H1/H2 in the relationship between the F plasmid and its host.