Effect of oxidizing agents and sulfhydryl group reagents on beta toxin from Clostridium perfringens type C

Recent insights into Clostridium perfringens beta-toxin

Clostridium perfringens beta-toxin is a key mediator of necrotizing enterocolitis and enterotoxemia. It is a pore-forming toxin (PFT) that exerts cytotoxic effect. Experimental investigation using piglet and rabbit intestinal loop models and a mouse infection model apparently showed that beta-toxin is the important pathogenic factor of the organisms. The toxin caused the swelling and disruption of HL-60 cells and formed a functional pore in the lipid raft microdomains of sensitive cells. These findings represent significant progress in the characterization of the toxin with knowledge on its biological features, mechanism of action and structure-function having been accumulated. Our aims here are to review the current progresses in our comprehension of the virulence of C. perfringens type C and the character, biological feature and structure-function of beta-toxin.

The p38 MAPK and JNK pathways protect host cells against Clostridium perfringens beta-toxin

Clostridium perfringens beta-toxin is an important agent of necrotic enteritis and enterotoxemia. Beta-toxin is a pore-forming toxin (PFT) that causes cytotoxicity. Two mitogen-activated protein kinase (MAPK) pathways (p38 and c-Jun N-terminal kinase [JNK]-like) provide cellular defense against various stresses. To investigate the role of the MAPK pathways in the toxic effect of beta-toxin, we examined cytotoxicity in five cell lines. Beta-toxin induced cytotoxicity in cells in the following order: THP-1 = U937 > HL-60 > BALL-1 = MOLT-4. In THP-1 cells, beta-toxin formed oligomers on lipid rafts in membranes and induced the efflux of K(+) from THP-1 cells in a dose- and time-dependent manner. The phosphorylation of p38 MAPK and JNK occurred in response to an attack by beta-toxin. p38 MAPK (SB203580) and JNK (SP600125) inhibitors enhanced toxin-induced cell death. Incubation in K(+)-free medium intensified p38 MAPK activation and cell death induced by the toxin, while incubation in K(+)-high medium prevented those effects. While streptolysin O (SLO) reportedly activates p38 MAPK via reactive oxygen species (ROS), we showed that this pathway did not play a major role in p38 phosphorylation in beta-toxin-treated cells. Therefore, we propose that beta-toxin induces activation of the MAPK pathway to promote host cell survival.

Clostridial toxins

Clostridia produce the highest number of toxins of any type of bacteria and are involved in severe diseases in humans and other animals. Most of the clostridial toxins are pore-forming toxins responsible for gangrenes and gastrointestinal diseases. Among them, perfringolysin has been extensively studied and it is the paradigm of the cholesterol-dependent cytolysins, whereas Clostridium perfringens epsilon-toxin and Clostridium septicum alpha-toxin, which are related to aerolysin, are the prototypes of clostridial toxins that form small pores. Other toxins active on the cell surface possess an enzymatic activity, such as phospholipase C and collagenase, and are involved in the degradation of specific cell-membrane or extracellular-matrix components. Three groups of clostridial toxins have the ability to enter cells: large clostridial glucosylating toxins, binary toxins and neurotoxins. The binary and large clostridial glucosylating toxins alter the actin cytoskeleton by enzymatically modifying the actin monomers and the regulatory proteins from the Rho family, respectively. Clostridial neurotoxins proteolyse key components of neuroexocytosis. Botulinum neurotoxins inhibit neurotransmission at neuromuscular junctions, whereas tetanus toxin targets the inhibitory interneurons of the CNS. The high potency of clostridial toxins results from their specific targets, which have an essential cellular function, and from the type of modification that they induce. In addition, clostridial toxins are useful pharmacological and biological tools.

Biological activities and pore formation of Clostridium perfringens beta toxin in HL 60 cells

Clostridium perfringens beta toxin is an important agent of necrotic enteritis. Of the 10 cell lines tested, only the HL 60 cell line was susceptible to beta toxin. The toxin induced swelling and lysis of the cell. Treatment of the cells with the toxin resulted in K+ efflux from the cells and Ca2+, Na+, and Cl- influxes. These events reached a maximum just before the cells were lysed by the toxin. Incubation of the cells with the toxin showed the formation of toxin complexes of about 191 and 228 kDa, which were localized in the domains that fulfilled the criteria of lipid rafts. The complex of 228 kDa was observed until 30 min after incubation, and only the complex of 191 kDa was remained after 60 min. Treatment of the cells with methyl-beta-cyclodextrin or cholesterol oxidase blocked binding of the toxin to the rafts and the toxin-induced K+ efflux and swelling. The toxin-induced Ca2+ influx and morphological changes were inhibited by an increase in the hydrodynamic diameter of polyethylene glycols from 200 to 400 and markedly or completely inhibited by polyethylene glycol 600 and 1000. However, these polyethylene glycols had no effect on the toxin-induced K+ efflux. The toxin induced carboxyfluorescein release from phosphatidyl-choline-cholesterol liposomes containing carboxyfluorescein and formed an oligomer with 228 kDa in a dose-dependent manner but did not form an oligomer with the 191-kDa complex. We conclude that the toxin acts on HL 60 cells by binding to lipid rafts and forming a functional oligomer with 228 kDa.

Involvement of tachykinin receptors in Clostridium perfringens beta-toxin-induced plasma extravasation

1 Clostridium perfringens beta-toxin causes dermonecrosis and oedema in the dorsal skin of animals. In the present study, we investigated the mechanisms of oedema induced by the toxin. 2 The toxin induced plasma extravasation in the dorsal skin of Balb/c mice. 3 The extravasation was significantly inhibited by diphenhydramine, a histamine 1 receptor antagonist. However, the toxin did not cause the release of histamine from mouse mastocytoma cells. 4 Tachykinin NK(1) receptor antagonists, [D-Pro(2), D-Trp(7,9)]-SP, [D-Pro(4), D-Trp(7,9)]-SP and spantide, inhibited the toxin-induced leakage in a dose-dependent manner. Furthermore, the non-peptide tachykinin NK(1) receptor antagonist, SR140333, markedly inhibited the toxin-induced leakage. 5 The leakage induced by the toxin was markedly reduced in capsaicin-pretreated mouse skin but the leakage was not affected by systemic pretreatment with a calcitonin gene-related peptide receptor antagonist (CGRP(8-37)). 6 The toxin-induced leakage was significantly inhibited by the N-type Ca(2+) channel blocker, omega-conotoxin MVIIA, and the bradykinin B(2) receptor antagonist, HOE140 (D-Arg-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin), but was not affected by the selective L-type Ca(2+) channel blocker, verapamil, the P-type Ca(2+) channel blocker, omega-agatoxin IVA, tetrodotoxin (TTX), the TTX-resistant Na(+) channel blocker, carbamazepine, or the sensory nerve conduction blocker, lignocaine. 7 These results suggest that plasma extravasation induced by beta-toxin in mouse skin is mediated via a mechanism involving tachykinin NK(1) receptors.

Clostridium perfringens beta-toxin is sensitive to thiol-group modification but does not require a thiol group for lethal activity

The beta-toxin gene isolated from Clostridium perfringens type B was expressed as a glutathione S-transferase (GST) fusion gene in Escherichia coli. The purified GST-beta-toxin fusion protein from the E. coli transformant cells was not lethal. The N-terminal amino acid sequence of the recombinant beta-toxin (r toxin) isolated by thrombin cleavage of the fusion protein was G-S-N-D-I-G-K-T-T-T. Biological activities and molecular mass of r toxin were indistinguishable from those of native beta-toxin (n toxin) purified from C. perfringens type C. Replacement of Cys-265 with alanine or serine by site-directed mutagenesis resulted in little loss of the activity. Treatment of C265A with N-ethylmaleimide (NEM), which inactivated lethal activity of r toxin and n toxin, led to no loss of the activity. The substitution of tyrosine or histidine for Cys-265 significantly diminished lethal activity. In addition, treatment of C265H with ethoxyformic anhydride which specifically modifies histidyl residue resulted in significant decrease in lethal activity, but that of r toxin with the agent did not. These results showed that replacement of the cysteine residue at position 265 with amino acids with large size of side chain or introduction of functional groups in the position resulted in loss of lethal activity of the toxin. Replacement of Tyr-266, Leu-268 or Trp-275 resulted in complete loss of lethal activity. Simultaneous administration of r toxin and W275A led to a decrease in lethal activity of beta-toxin. These observations suggest that the site essential for the activity is close to the cysteine residue.

Site-directed mutagenesis of Clostridium perfringens beta-toxin: expression of wild-type and mutant toxins in Bacillus subtilis

Recombinant beta-toxin has been expressed and secreted from Bacillus subtilis. Biological activity was tested in vivo and in vitro. The lethal dose in mice was determined. Hemolysis of rabbit and sheep erythrocytes was tested but no effect was observed. Seven mutant proteins were produced. Targets for mutagenesis were mostly selected on the basis of the similarity between beta-toxin and alpha-toxin from Staphylococcus aureus, a pore-forming toxin. Mutations of two amino acids affected the lethal dose in mice. Both residues have counterparts in the membrane binding region of alpha-toxin. Alteration of the single cysteine residue did not affect protein function, contrary to previous suggestions.

Expression and purification of Clostridium perfringens beta-toxin glutathione S-transferase fusion protein

The beta-toxin gene from Clostridium perfringens type C was cloned and expressed as a glutathione S-transferase fusion protein in Escherichia coli. The DNA sequence was determined and compared to the type B sequence. Two nucleotide differences were found in the protein coding sequence, resulting in one amino acid difference between the two proteins. The purified beta-toxin fusion protein is not toxic in mice, but rabbit antiserum raised against it neutralises the toxic effect of C. perfringens type C culture filtrate in mice.

Molecular genetic analysis of beta-toxin of Clostridium perfringens reveals sequence homology with alpha-toxin, gamma-toxin, and leukocidin of Staphylococcus aureus

Oligonucleotide probes designed on the basis of the N-terminal sequence of Clostridium perfringens beta-toxin were used to isolate the encoding gene (cpb). The nucleotide sequence of cpb was determined, and on the basis of DNA hybridization experiments it was shown that the gene is found only in type B and C strains of C. perfringens. The deduced amino acid sequence of the beta-toxin revealed homology with the alpha-toxin, gamma-toxin, and leukocidin of Staphylococcus aureus. The beta-toxin purified from C. perfringens appeared to exist in monomeric and multimeric forms. Recombinant beta-toxin, produced in Escherichia coli, appeared to be mainly in the multimeric form.

Effect of p-chloromercuribenzoate on Clostridium perfringens beta toxin

p-Chloromercuribenzoate (PCMB) was shown to bind to Clostridium perfringens beta toxin. Treatment of the toxin with N-ethylmaleimide (NEM), 5,5'-dithio-bis(2-nitro-benzoic acid) (DTNB), o-iodosobenzoate (OIBA) and metal ions such as Cu2+ and Ag+ decreased the lethal activity, but PCMB did not affect the lethal activity. On the other hand, the binding of PCMB to the toxin was inhibited by DTNB and NEM in a dose-dependent manner. Furthermore, the lethal activity of beta toxin pretreated with PCMB was not blocked by treatment with NEM, DTNB, OIBA, Cu2+ and Ag+. However, the PCMB-treated toxin treated with reduced glutathione, dithiothreitol, 2-mercaptoethanol, liver homogenate or serum from mice was inactivated by NEM.

Dissociation of various biological activities of Clostridium perfringens alpha toxin by chemical modification

The effect of N-acetylimidazole, tetranitromethane, maleic anhydride and N-ethylmaleimide on various biological activities of Clostridium perfringens alpha (alpha)-toxin was investigated. Treatment of the toxin with N-acetylimidazole, tetranitromethane or maleic anhydride resulted in significant reduction of lethal, hemolytic and platelet-aggregating activities and phospholipase C activity (EY activity), as measured by increased turbidity in egg yolk emulsions. However, EY activity was more resistant to these reagents than lethal, hemolytic or aggregating activities. Phospholipase C activity (PN activity) as measured by hydrolysis of p-nitrophenylphosphorylcholine was retained after treatment with N-acetylimidazole, tetranitromethane or maleic anhydride. The activities of the toxin were not inactivated by treatment with N-ethylmaleimide. These data suggest that alpha-toxin contains multiple sites for biological activities of the toxin.

Purification and characterization of Clostridium perfringens beta toxin

A new procedure for the purification of beta toxin from culture supernatant fluid of Clostridium perfringens was established. The procedure consists of ammonium sulfate fractionation, affinity chromatography on zinc-chelate Sepharose and gel filtration on Toyopearl HW 60. Beta toxin was purified about 460-fold from the ammonium sulfate fraction with a yield of about 60% in terms of lethality of the toxin. The molecular weight of the toxin, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and sucrose gradient centrifugation, was approximately 40,000. The isoelectric point was 5.6. The minimal necrotic dose for guinea pigs was approximately 2 ng. The 50% lethal doses for adult mice were 310 ng/kg and 4.5 micrograms/kg, when injected i.v. and i.p., respectively.

Purification and characterization of Clostridium sordellii lethal toxin and cross-reactivity with Clostridium difficile cytotoxin

Lethal toxin (LT) was purified from Clostridium sordellii IP82 by DEAE-Trisacryl, Ultrogel AcA3-4 gel filtration, and hydroxyapatite column chromatography. The molecular weight of purified LT was estimated to be 240,000 to 250,000, and the pI was at pH 4.55. LT was lethal for mice by intraperitoneal injection (3.4 X 10(5) mouse lethal doses per mg of protein), cytotoxic for Vero cells (6.1 X 10(4) cytotoxic units per mg of protein), erythematous and edematous by intradermal injection in guinea pigs, and induced a moderate fluid accumulation in the guinea pig intestinal loop test. The lethal activity was inactivated by N-bromosuccinimide, N-chlorosuccinimide, chloramine-T, and sodium dodecyl sulfate. The data suggest that tryptophan and methionine residues present in the toxin are important for lethal activity. Furthermore, LT was inactivated by oxidized glutathione and activated by dithiothreitol. Inactivation by sulfhydryl-group reagents 5,5'-dithiobis(2-nitrobenzoic acid) and iodoacetamide was only obtained with dithiothreitol-treated LT. Thiol groups which are protected as a disulfide bond(s) seem to be essential for the LT activity. A specific antiserum against LT neutralized the biological activities of LT and also cytotoxic activity and lethal activity of Clostridium difficile toxin B but not of C. difficile toxin A. However, this serum did not recognize antigen from C. difficile culture supernatant by immunoblotting. It was concluded that antibodies prepared from C. sordellii LT that neutralized C. difficile cytotoxic activity recognized a low number of epitopes or tertiary structures of C. difficile cytotoxin.

Effect of Clostridium perfringens beta toxin on blood pressure of rats

Guanethidine treatment or adrenal medullectomy significantly inhibited the elevation in blood pressure induced by Clostridium perfringens beta toxin, and the combination of the two drastically reduced the pressure rise, to less than 19% of that in control rats. When rats were pretreated with tetrodotoxin or hexamethonium, the toxin-evoked rise was significantly inhibited. Elevation in blood pressure induced by the toxin in spinal rats tended to be less than that in control rats. When investigated by a microscopical technique, arteriolar constriction in the mesenteric vasculature was observed after the blood pressure elevation induced by the toxin reached a maximum. Blood flow in the skin decreased with an increase in blood pressure following intravenous injection of the toxin. It is concluded that beta toxin acts on the autonomic nervous system and produces arterial constriction.

Pharmacological effect of beta toxin of Clostridium perfringens type C on rats

The biological effect of purified beta toxin of Clostridium perfringens type C in vivo was investigated. After intravenous injection of the purified beta toxin into rats, a rise in blood pressure and a simultaneous fall in heart rate were observed. After the blood pressure reached a maximum, the heart rate recovered gradually, and electrocardiographic and respiratory changes began. The rise in blood pressure induced by beta toxin tended to be proportional to the amount of toxin. The latent period between the injection of toxin and the onset of the increase, and also the time between the injection and the maximum pressure induced by the toxin decreased with increasing concentration of the toxin. A good correlation was found between the factor producing the rise in blood pressure and beta toxin. Alpha adrenergic and ganglionic blocking agents reduced blood pressure levels elevated by beta toxin. The data suggest that the toxin causes a release of catecholamines, and that the increase in blood pressure was induced by released catecholamines.