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

First Comparative Analysis of Clostridium septicum Genomes Provides Insights Into the Taxonomy, Species Genetic Diversity, and Virulence Related to Gas Gangrene

Clostridium septicum is a Gram-positive, toxin-producing, and spore-forming bacterium that is recognized, together with C. perfringens, as the most important etiologic agent of progressive gas gangrene. Clostridium septicum infections are almost always fatal in humans and animals. Despite its clinical and agricultural relevance, there is currently limited knowledge of the diversity and genome structure of C. septicum. This study presents the complete genome sequence of C. septicum DSM 7534T type strain as well as the first comparative analysis of five C. septicum genomes. The taxonomy of C. septicum, as revealed by 16S rRNA analysis as well as by genomic wide indices such as protein-based phylogeny, average nucleotide identity, and digital DNA–DNA hybridization indicates a stable clade. The composition and presence of prophages, CRISPR elements and accessory genetic material was variable in the investigated genomes. This is in contrast to the limited genetic variability described for the phylogenetically and phenotypically related species Clostridium chauvoei. The restriction-modification (RM) systems between two C. septicum genomes were heterogeneous for the RM types they encoded. C. septicum has an open pangenome with 2,311 genes representing the core genes and 1,429 accessory genes. The core genome SNP divergence between genome pairs varied up to 4,886 pairwise SNPs. A vast arsenal of potential virulence genes was detected in the genomes studied. Sequence analysis of these genes revealed that sialidase, hemolysin, and collagenase genes are conserved compared to the α-toxin and hyaluronidase genes. In addition, a conserved gene found in all C. septicum genomes was predicted to encode a leucocidin homolog (beta-channel forming cytolysin) similar (71.10% protein identity) to Clostridium chauvoei toxin A (CctA), which is a potent toxin. In conclusion, our results provide first, valuable insights into strain relatedness and genomic plasticity of C. septicum and contribute to our understanding of the virulence mechanisms of this important human and animal pathogen.

Molecular docking analysis of P2X7 receptor with the beta toxin from Clostridium perfringens

Clostridium perfringens beta-toxin (CPB) is linked to necrotic enteritis (over proliferation of bacteria) in several species showing cytotoxic effect on primary porcine endothelial and human precursor immune cells. P2X7 receptor on THP-1 cells is known to bind CPB. This is critical to understand the mechanism of pore formation for effective drug design. The structure of CPB and P2X7 receptor proteins were modeled using standard molecular modeling procedures (I-TASSER and Robetta server). This is followed by protein-protein docking (HADDOCK server) to study their molecular interaction. Interacting residues (19 residues from CPB and 21 residues from P2X7) were identified using the PISA server. Thus, we document the molecular docking analysis of P2X7 receptor with the beta toxin from Clostridium perfringens towards drug design and development of drugs to control necrotic enteritis.

Role of pannexin 1 in Clostridium perfringens beta-toxin-caused cell death

BACKGROUND

Beta-toxin produced by Clostridium perfringens is a key virulence factor of fatal hemorrhagic enterocolitis and enterotoxemia. This toxin belongs to a family of β-pore-forming toxins (PFTs). We reported recently that the ATP-gated P2X₇ receptor interacts with beta-toxin. The ATP-release channel pannexin 1 (Panx1) is an important contributor to P2X₇ receptor signaling. Hence, we investigated the involvement of Panx1 in beta-toxin-caused cell death.

METHODS

We examined the effect of Panx1 in beta-toxin-induced cell death utilizing selective antagonists, knockdown of Panx1, and binding using dot-blot analysis. Localization of Panx1 and the P2X₇ receptor after toxin treatment was determined by immunofluorescence staining.

RESULTS

Selective Panx1 antagonists (carbenoxolone [CBX], probenecid, and Panx1 inhibitory peptide) prevented beta-toxin-caused cell death in THP-1 cells. CBX did not block the binding of the toxin to cells. Small interfering knockdown of Panx1 blocked beta-toxin-mediated cell death through inhibiting the oligomer formation of the toxin. Beta-toxin triggered a transient ATP release from THP-1 cells, but this early ATP release was blocked by CBX. ATP scavengers (apyrase and hexokinase) inhibited beta-toxin-induced cytotoxicity. Furthermore, co-administration of ATP with beta-toxin enhanced the binding and cytotoxicity of the toxin.

CONCLUSIONS

Based on our results, Panx1 activation is achieved through the interaction of beta-toxin with the P2X₇ receptor. Then, ATP released by the Panx1 channel opening promotes oligomer formation of the toxin, leading to cell death.

GENERAL SIGNIFICANCE

Pannexin 1 is a novel candidate therapeutic target for beta-toxin-mediated disease.

Role of P2X7 receptor in Clostridium perfringens beta-toxin-mediated cellular injury

BACKGROUND

Clostridium perfringens beta-toxin is a pore-forming toxin (PFT) and an important agent of necrotic enteritis and enterotoxemia. We recently reported that beta-toxin strongly induced cell death in THP-1 cells via the formation of oligomers. We here describe that the P2X(7) receptor, which is an ATP receptor, interacts with beta-toxin.

METHODS

We tested the role of P2X(7) receptor in beta-toxin-induced toxicity using specific inhibitors, knockdown of receptor, expression of the receptor and interaction by dot-blot assay. The potency of P2X(7) receptor was further determined using an in vivo mouse model.

RESULTS

Selective P2X(7) receptor antagonists (oxidized ATP (o-ATP), oxidized ADP, and Brilliant Blue G (BBG)) inhibited beta-toxin-induced cytotoxicity in THP-1 cells. o-ATP also blocked the binding of beta-toxin to cells. The P2X(7) receptor and beta-toxin oligomer were localized in the lipid rafts of THP-1 cells. siRNA for the P2X(7) receptor inhibited toxin-induced cytotoxicity and binding of the toxin. In contrast, the siRNA knockdown of P2Y(2) or P2Y(6) had no effect on beta-toxin-induced cytotoxicity. The addition of beta-toxin to P2X(7)-transfected HEK-293 cells resulted in binding of beta-toxin oligomer. Moreover, beta-toxin specifically bound to immobilized P2X(7) receptors in vitro and colocalized with the P2X(7) receptor on the THP-1 cell surface. Furthermore, beta-toxin-induced lethality in mice was blocked by the preadministration of BBG.

CONCLUSIONS

The results of this study indicate that the P2X(7) receptor plays a role in beta-toxin-mediated cellular injury.

GENERAL SIGNIFICANCE

P2X(7) receptor is a potential target for the treatment of C. perfringens type C infection.

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.

Identification and characterization of Clostridium perfringens beta toxin variants with differing trypsin sensitivity and in vitro cytotoxicity activity

By producing toxins, Clostridium perfringens causes devastating diseases of both humans and animals. C. perfringens beta toxin (CPB) is the major virulence determinant for type C infections and is also implicated in type B infections, but little is known about the CPB structure-function relationship. Amino acid sequence comparisons of the CPBs made by 8 randomly selected isolates identified two natural variant toxins with four conserved amino acid changes, including a switch of E to K at position 168 (E168K) that introduces a potential trypsin cleavage site into the CPB protein of strain JGS1076. To investigate whether this potential trypsin cleavage site affects sensitivity to trypsin, a primary host defense against this toxin, the two CPB variants were assayed for their trypsin sensitivity. The results demonstrated a significant difference in trypsin sensitivity, which was linked to the E168K switch by using site-directed recombinant CPB (rCPB) mutants. The natural CPB variants also displayed significant differences in their cytotoxicity to human endothelial cells. This cytotoxicity difference was mainly attributable to increased host cell binding rather than the ability to oligomerize or form functional pores. Using rCPB site-directed mutants, differences in cytotoxicity and host cell binding were linked to an A300V amino acid substitution in the strain JGS1076 CPB variant that possessed more cytotoxic activity. Mapping of sequence variations on a CPB structure modeled using related toxins suggests that the E168K substitution is surface localized and so can interact with trypsin and that the A300V substitution is located in a putative binding domain of the CPB toxin.

Cytotoxin CctA, a major virulence factor of Clostridium chauvoei conferring protective immunity against myonecrosis

OBJECTIVE

The purpose of this study was to determine the identity of the major toxin of Clostridium chauvoei, an important pathogen of cattle causing black leg and to determine its value as a protective antigen in vaccines against myonecrosis.

METHODS

Genomic sequence analysis was used to determine potential virulence genes of C. chauvoei. Subsequently, the putative toxin candidate gene was cloned and expressed to obtain recombinant toxin. This toxin was investigated for its cytotoxic activity, hemolysis and its potential as a protective antigen in the guinea pig potency assay.

RESULTS

A novel protein toxin, named Clostridium chauvoei toxin A (CctA) that belongs to the family of β-barrel pore forming toxins of the leucocidin superfamily of bacterial toxins was discovered by whole genome sequence analysis. The corresponding gene cctA was found in all strains of C. chauvoei analyzed, isolated from various geographical areas over the globe during the last 50 years, but not in other pathogenic Clostridium species. Native CctA and recombinant rCctA produced in Escherichia coli in the form of a rCctA::NusA fusion protein or thrombin processed rCctA were highly cytotoxic for Embryonic Calf Nasal Epithelial (ECaNEp) cells and had high haemolytic activity against sheep erythrocytes in standard haemolysis assays. Polyclonal anti-rCctA rabbit antibodies fully neutralized the cytotoxic and haemolytic activity, not only of rCctA but also of supernatants from cultures of the various C. chauvoei strains, indicating that CctA is the main cytotoxic and haemolytic substance secreted by C. chauvoei. Using a standard vaccine release procedure, we demonstrated that vaccination of guinea pigs with CctA in the form of a fusion protein with the E. coli heat labile toxin B subunit (rCctA::LTB) as a peptide adjuvant protected the animals against challenge with spores of virulent C. chauvoei.

CONCLUSIONS

CctA is the major virulence factor of C. chauvoei and the main protective antigen in vaccines against blackleg.

NetB, a pore-forming toxin from necrotic enteritis strains of Clostridium perfringens

The Clostridium perfringens necrotic enteritis B-like toxin (NetB) is a recently discovered member of the β-barrel pore-forming toxin family and is produced by a subset of avian C. perfringens type A strains. NetB is cytotoxic for avian cells and is associated with avian necrotic enteritis. This review examines the current state of knowledge of NetB: its role in pathogenesis, its distribution and expression in C. perfringens and its vaccine potential.

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.

Clostridium perfringens delta toxin is sequence related to beta toxin, NetB, and Staphylococcus pore-forming toxins, but shows functional differences

Clostridium perfringens produces numerous toxins, which are responsible for severe diseases in man and animals. Delta toxin is one of the three hemolysins released by a number of C. perfringens type C and possibly type B strains. Delta toxin was characterized to be cytotoxic for cells expressing the ganglioside G_M2 in their membrane. Here we report the genetic characterization of Delta toxin and its pore forming activity in lipid bilayers. Delta toxin consists of 318 amino acids, its 28 N-terminal amino acids corresponding to a signal peptide. The secreted Delta toxin (290 amino acids; 32619 Da) is a basic protein (pI 9.1) which shows a significant homology with C. perfringens Beta toxin (43% identity), with C. perfringens NetB (40% identity) and, to a lesser extent, with Staphylococcus aureus alpha toxin and leukotoxins. Recombinant Delta toxin showed a preference for binding to G_M2, in contrast to Beta toxin, which did not bind to gangliosides. It is hemolytic for sheep red blood cells and cytotoxic for HeLa cells. In artificial diphytanoyl phosphatidylcholine membranes, Delta and Beta toxin formed channels. Conductance of the channels formed by Delta toxin, with a value of about 100 pS to more than 1 nS in 1 M KCl and a membrane potential of 20 mV, was higher than those formed by Beta toxin and their distribution was broader. The results of zero-current membrane potential measurements and single channel experiments suggest that Delta toxin forms slightly anion-selective channels, whereas the Beta toxin channels showed a preference for cations under the same conditions. C. perfringens Delta toxin shows a significant sequence homolgy with C. perfringens Beta and NetB toxins, as well as with S. aureus alpha hemolysin and leukotoxins, but exhibits different channel properties in lipid bilayers. In contrast to Beta toxin, Delta toxin recognizes G_M2 as receptor and forms anion-selective channels.

NetB, a new toxin that is associated with avian necrotic enteritis caused by Clostridium perfringens

For over 30 years a phospholipase C enzyme called alpha-toxin was thought to be the key virulence factor in necrotic enteritis caused by Clostridium perfringens. However, using a gene knockout mutant we have recently shown that alpha-toxin is not essential for pathogenesis. We have now discovered a key virulence determinant. A novel toxin (NetB) was identified in a C. perfringens strain isolated from a chicken suffering from necrotic enteritis (NE). The toxin displayed limited amino acid sequence similarity to several pore forming toxins including beta-toxin from C. perfringens (38% identity) and alpha-toxin from Staphylococcus aureus (31% identity). NetB was only identified in C. perfringens type A strains isolated from chickens suffering NE. Both purified native NetB and recombinant NetB displayed cytotoxic activity against the chicken leghorn male hepatoma cell line LMH; inducing cell rounding and lysis. To determine the role of NetB in NE a netB mutant of a virulent C. perfringens chicken isolate was constructed by homologous recombination, and its virulence assessed in a chicken disease model. The netB mutant was unable to cause disease whereas the wild-type parent strain and the netB mutant complemented with a wild-type netB gene caused significant levels of NE. These data show unequivocally that in this isolate a functional NetB toxin is critical for the ability of C. perfringens to cause NE in chickens. This novel toxin is the first definitive virulence factor to be identified in avian C. perfringens strains capable of causing NE. Furthermore, the netB mutant is the first rationally attenuated strain obtained in an NE-causing isolate of C. perfringens; as such it has considerable vaccine potential.

Clostridium perfringens can cause gas gangrene and food poisoning in humans and causes several enterotoxemic diseases in animals including avian necrotic enteritis. This disease affects all chicken producing countries worldwide and is a considerable burden on the commercial chicken production industry. Until recently alpha-toxin was thought to be the major virulence factor involved in necrotic enteritis. However, by using an alpha-toxin null mutant it has been demonstrated that this toxin is not essential for disease. This paper details the identification and characterisation of a novel toxin, NetB, and provides evidence that the protein is an essential factor in causing necrotic enteritis in chickens. NetB has limited protein sequence identity to the beta-toxin of C. perfringens, which causes mucosal necrosis of the small intestine in humans and animals. We demonstrate that NetB null mutants can no longer cause disease in chickens, whereas both the wild-type and mutant complemented with a wild-type netB gene caused significant levels of necrotic enteritis. The identification of this important toxin advances our understanding of the pathogenesis of the disease and opens significant opportunities for the development of novel vaccines against necrotic enteritis in poultry.

Involvement of tumour necrosis factor-alpha in Clostridium perfringens beta-toxin-induced plasma extravasation in mice

BACKGROUND AND PURPOSE

Clostridium perfringens beta-toxin, an important agent of necrotic enteritis, causes plasma extravasation due to the release of a tachykinin NK(1) receptor agonist in mouse skin. In this study, we investigated the role of cytokines in beta-toxin-induced plasma extravasation.

EXPERIMENTAL APPROACH

Male Balb/c, C3H/HeN and C3H/HeJ mice were anaesthetized with pentobarbitone and beta-toxin was injected i.d. into shaved dorsal skin. SR140333, capsaicin, chlorpromazine and pentoxifylline were given as pretreatment when required before the injection of the toxin. Cytokines in the dorsal skin were measured by ELISA.

KEY RESULTS

Injection (i.d.) of beta-toxin induced a dose-dependent increase in dermal TNF-alpha and interleukin (IL)-1beta levels with a concomitant increase in plasma extravasation, but not the release of IL-6. SR140333 and capsaicin significantly inhibited the toxin-induced release of TNF-alpha and IL-1beta. The plasma extravasation and the release of TNF-alpha induced by beta-toxin were significantly inhibited by chlorpromazine and pentoxifylline which inhibit the release of TNF-alpha. The toxin-induced plasma extravasation in mouse skin was attenuated by pretreatment with a monoclonal antibody against TNF-alpha, but not anti-IL-1beta. Furthermore, the toxin caused an increase in plasma extravasation in both C3H/HeN (TLR4-intact) and C3H/HeJ (TLR4-deficient) mice. In C3H/HeN mice, the toxin-induced leakage was not inhibited by pretreatment with anti-TLR4/MD-2 antibody.

CONCLUSIONS AND IMPLICATIONS

These observations show that beta-toxin-induced plasma extravasation in mouse skin is related to the release of TNF-alpha via the mechanism involving tachykinin NK(1) receptors, but not via TLR4.

A novel toxin homologous to large clostridial cytotoxins found in culture supernatant of Clostridium perfringens type C

An unknown cytotoxin was identified in the culture supernatant of Clostridium perfringens type C. The cytotoxin, named TpeL, which was purified using mAb-based affinity chromatography, had a lethal activity of 62 minimum lethal dose (MLD) mg(-1) in mice and a cytotoxic activity of 6.2x10(5) cytotoxic units (CU) mg(-1) in Vero cells. The nucleotide sequence of TpeL was determined. The entire ORF had a length of 4953 bases, and the same nucleotide sequence was not recorded in the GenBank/EMBL/DDBJ databases. The molecular mass calculated from the deduced amino acid sequence was 191 kDa, and a signal peptide region was not found within the ORF. The deduced amino acid sequence exhibited 30-39 % homology to Clostridium difficile toxins A (TcdA) and B (TcdB), Clostridium sordellii lethal toxin (TcsL) and Clostridium novyi alpha-toxin (TcnA). The amino acid sequence of TpeL is shorter than these toxins, and the homologous region was located at the N-terminal site. Eighteen strains of C. perfringens types A, B and C were surveyed for the presence of the tpeL gene by PCR. The tpeL gene was detected in all type B (one strain) and C strains (five strains), but not in any type A strains (12 strains). TpeL was detected in culture filtrates of the five type C strains by dot-blot analysis, but not in the type B strain. It was concluded that TpeL is a novel toxin similar to the known large clostridial cytotoxins. Furthermore, the data indicated that TpeL is produced by many C. perfringens type C strains.

Role of tyrosine-57 and -65 in membrane-damaging and sphingomyelinase activities of Clostridium perfringens alpha-toxin

Clostridium perfringens alpha-toxin (370 residues) is a major virulence factor in the pathogenesis of gas gangrene. The toxin is composed of an N-terminal domain (1-250 residues) where lies the catalytic site and a C-terminal domain (251-370 residues), the Ca(2+)-binding domain, responsible for binding to membranes. The role of Tyr-57 and Tyr-65 close to the catalytic pocket (site) in the N-domain was investigated. Replacement of Tyr-57 and -65 with alanine, leucine, or phenylalanine did not affect the sphingomyelinase activity of the toxin for sodium deoxycholate-solubilized shingomyelin. However, the substitution of Tyr-57 and -65 with alanine or leucine resulted in a radical reduction in the hemolysis of sheep erythrocytes, the release of carboxyfluorescein from shingomyelin-cholesterol (1:1) liposomes, and a significant decrease in binding to the liposomes. The binding of variant toxins, Y57C/C169L and Y65C/C169L, labeled with the environmentally sensitive fluorophore, acrylodan, to the liposomes suggested insertion of the variants in a hydrophobic environment in the bilayer. These observations suggested that Tyr-57 and -65 play a role in the penetration of the toxin into the bilayer of membranes and access of the catalytic site to sphingomyelin in membranes, but do not participate in the enzymatic activity.

The enteric toxins of Clostridium perfringens

The Gram-positive pathogen Clostridium perfringens is a major cause of human and veterinary enteric disease largely because this bacterium can produce several toxins when present inside the gastrointestinal tract. The enteric toxins of C. perfringens share two common features: (1) they are all single polypeptides of modest (approximately 25-35 kDa) size, although lacking in sequence homology, and (2) they generally act by forming pores or channels in plasma membranes of host cells. These enteric toxins include C. perfringens enterotoxin (CPE), which is responsible for the symptoms of a common human food poisoning and acts by forming pores after interacting with intestinal tight junction proteins. Two other C. perfringens enteric toxins, epsilon-toxin (a bioterrorism select agent) and beta-toxin, cause veterinary enterotoxemias when absorbed from the intestines; beta- and epsilon-toxins then apparently act by forming oligomeric pores in intestinal or extra-intestinal target tissues. The action of a newly discovered C. perfringens enteric toxin, beta2 toxin, has not yet been defined but precedent suggests it might also be a pore-former. Experience with other clostridial toxins certainly warrants continued research on these C. perfringens enteric toxins to develop their potential as therapeutic agents and tools for cellular biology.

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.

Binding component of Clostridium perfringens iota-toxin induces endocytosis in Vero cells

Clostridium perfringens iota-toxin is a binary toxin consisting of two individual proteins, the binding component (Ib) and the enzyme component (Ia). Wild-type Ib bound to Vero cells at 4 and 37 degrees C and formed oligomers at 37 degrees C but not at 4 degrees C. The Ib-induced K(+) release from the cells was dependent on the oligomer formation of Ib in the cells, but the oligomer formation did not induce rounding activity or cytotoxicity. After incubation of the cells with recombinant Ib (rIb) at 37 degrees C, the Ib oligomer in the cell became resistant to pronase treatment with time, but the Ib monomer was sensitive to the treatment. Furthermore, treatment of Vero cells with rIb in the presence of bafilomycin, methylamine, or ethylamine resulted in accumulation of the oligomer in the cells but had no effect on K(+) release. Moreover, incubation with Ib plus Ia in the presence of these agents caused no rounding in the cells. These observations suggest that Ib binds to Vero cells, itself oligomerizing to form ion-permeable channels and that the formation of oligomer then induces endocytosis.

Mode of action of beta-barrel pore-forming toxins of the staphylococcal alpha-hemolysin family

Staphylococcal alpha-hemolysin is the prototype of a family of bacterial exotoxins with membrane-damaging function, which share sequence and structure homology. These toxins are secreted in a soluble form which finally converts into a transmembrane pore by assembling an oligomeric beta-barrel, with hydrophobic residues facing the lipids and hydrophilic residues facing the lumen of the channel. Besides alpha-hemolysin the family includes other single chain toxins forming homo-oligomers, e.g. beta-toxin of Clostridium perfringens, hemolysin II and cytotoxin K of Bacillus cereus, but also the staphylococcal bi-component toxins, like gamma-hemolysins and leucocidins, which are only active as the combination of two similar proteins which form hetero-oligomers. The molecular basis of membrane insertion has become clearer after the determination of the crystal structure of both the oligomeric pore and the soluble monomer. Studies on this family of beta-barrel pore-forming toxins are important for many aspects: (i) they are involved in serious pathologies of humans and farmed animals, (ii) they are a good model system to investigate protein-membrane interaction and (iii) they are the basic elements for the construction of nanopores with biotechnological applications in various fields.

Role of tryptophan-1 in hemolytic and phospholipase C activities of Clostridium perfringens alpha-toxin

Replacement of the Trp-1 in Clostridium perfringens alpha-toxin with tyrosine caused no effect on hemolytic and phospholipase C (PLC) activities or on binding to the zinc ion, but that of the residue with alanine, glycine and histidine led to drastic decreases in these activities and a significant reduction in binding to the zinc ion. The hemolytic and PLC activities of W1H and W1A were significantly increased by the preincubation of these variant toxins with zinc ions, but the preincubation of W1G with the metal ion caused little effect on these activities. Gly-Ile-alpha-toxin, which contained an additional Gly-Ile linked to the N-terminal amino acid of alpha-toxin, did not show hemolytic activity, but showed about 6% PLC activity of the wild-type toxin. A mutant toxin, which contained an additional Gly-Ile linked to the N-terminus of a protein lacking 4 N-terminal residues of alpha-toxin, showed about 1 and 6% hemolytic and PLC activities of the wild-type toxin, respectively. Incubation of the mutant toxin with zinc ions caused a significant increase in PLC activity. These observations suggested that Trp-1 is not essential for toxin activity, but plays a role in binding to zinc ions.

Clostridium perfringens beta-toxin forms potential-dependent, cation-selective channels in lipid bilayers

Recombinant beta-toxin from Clostridium perfringens type C was found to increase the conductance of bilayer lipid membranes (BLMs) by inducing channel activity. The channels exhibited a distribution of conductances within the range of 10 to 380 pS, with the majority of the channels falling into two categories of conductance at 110 and 60 pS. The radii of beta-toxin pores found for the conductance states of 110 and 60 pS were 12.7 and 11.1 A, respectively. The single channels and the steady-state currents induced by beta-toxin across the BLMs exhibited ideal monovalent cation selectivity. Addition of divalent cations (Zn(2+), Cd(2+), or Mg(2+)) at a concentration of 2 mM increased the rate of beta-toxin insertion into BLMs and the single-channel conductance, while application of 5 mM Zn(2+) to a beta-toxin-induced steady-state current decreased the inward current by approximately 45%. The mutation of arginine 212 of beta-toxin to aspartate, previously shown to increase the 50% lethal dose of beta-toxin for mice nearly 13-fold, significantly reduced the ability of beta-toxin to form channels. These data support the hypothesis that the lethal action of beta-toxin is based on the formation of cation-selective pores in susceptible cells.