[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin (CPE) causes the gastrointestinal symptoms of the second most common bacterial foodborne illness. Previous studies suggested that a region named TM1, which has amphipathic characteristics and spans from amino acids 81 to 106 of the native CPE protein, forms a β-hairpin involved in β-barrel pore formation. To further explore the potential role of TM1 in pore formation, the single Cys naturally present in CPE at residue 186 was first altered to alanine by mutagenesis; the resultant rCPE variant, named C186A, was shown to retain cytotoxic properties. Cys scanning mutagenesis was then performed where individual Cys mutations were introduced into each TM1 residue of the C186A variant. When those Cys variants were characterized, three variants were identified that exhibit reduced cytotoxicity despite possessing similar binding and oligomerization abilities as the C186A variant from which they were derived. Pronase challenge experiments suggested that the reduced cytotoxicity of those two Cys variants, i.e., F91C and F95C, which model to the tip of the β-hairpin, was attributable to a lessened ability of these variants to insert into membranes after oligomerization. In contrast, another Cys variant, i.e., G103C, with impaired cytotoxicity apparently inserted into membranes after oligomerization but could not form a pore with a fully functional channel. Collectively, these results support the TM1 region forming a β-hairpin as an important step in CPE insertion and pore formation. Furthermore, this work identifies the first amino acid residues specifically involved in those two steps in CPE action.
Full-text · Article · Sep 2012 · Infection and immunity
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin (CPE) is a major cause of food poisoning and antibiotic-associated diarrhea. Upon its release from C. perfringens spores, CPE binds to its receptor, claudin, at the tight junctions between the epithelial cells of the gut wall and subsequently forms pores in the cell membranes. A number of different complexes between CPE and claudin have been observed, and the process of pore formation has not been fully elucidated. We have determined the three-dimensional structure of the soluble form of CPE in two crystal forms by X-ray crystallography, to a resolution of 2.7 and 4.0 Å, respectively, and found that the N-terminal domain shows structural homology with the aerolysin-like β-pore-forming family of proteins. We show that CPE forms a trimer in both crystal forms and that this trimer is likely to be biologically relevant but is not the active pore form. We use these data to discuss models of pore formation.
Full-text · Article · Aug 2011 · Journal of Molecular Biology
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens is a Gram-positive anaerobic species of bacterium that is notable for its ability to produce a plethora of toxins, including membrane-active toxins (alpha-toxins), pore-forming toxins (-toxins) and binary toxins (iota-toxins). Here, the crystallization of the full-length wild-type C. perfringens enterotoxin is reported, which is the causative agent of the second most prevalent food-borne illness in the United States and has been implicated in many other gastrointestinal pathologies. Several crystal forms were obtained. However, only two of these optimized crystal forms (I and II) were useable for X-ray diffraction data collection. The form I crystals diffracted to d(min) = 2.7 A and belonged to space group C2, while the form II crystals diffracted to d(min) = 4 A and belonged to space group P2(1)3.
Full-text · Article · Jul 2010 · Acta Crystallographica Section F Structural Biology and Crystallization Communications
[Show abstract][Hide abstract] ABSTRACT: The 24-member claudin protein family plays a key role in maintaining the normal structure and function of epithelial tight junctions. Previous studies with fibroblast transfectants and naturally sensitive Caco-2 cells have also implicated certain claudins (e.g., Claudin-4) as receptors for Clostridium perfringens enterotoxin (CPE). The present study first provided evidence that the second extracellular loop (ECL-2) of claudins is specifically important for mediating the host cell binding and cytotoxicity of native CPE. Rat fibroblast transfectants expressing a Claudin-4 chimera, where the natural ECL-2 was replaced by ECL-2 from Claudin-2, exhibited no CPE-induced cytotoxicity. Conversely, CPE bound to, and killed, CPE-treated transfectants expressing a Claudin-2 chimera with a substituted ECL-2 from Claudin-4. Site-directed mutagenesis was then used to alter an ECL-2 residue that invariably aligns as N in claudins known to bind native CPE but as D or S in claudins that cannot bind CPE. Transfectants expressing a Claudin-4(N149D) mutant lost the ability to bind or respond to CPE, while transfectants expressing a Claudin-1 mutant with the corresponding ECL-2 residue changed from D to N acquired CPE binding and sensitivity. Identifying carriage of this N residue in ECL-2 as being important for native CPE binding helps to explain why only certain claudins can serve as CPE receptors. Finally, preincubating CPE with soluble recombinant Claudin-4, or Claudin-4 fragments containing ECL-2 specifically blocked the cytotoxicity on Caco-2 cells. This result opens the possibility of using receptor claudins as therapeutic decoys to ameliorate CPE-mediated intestinal disease.
Preview · Article · Nov 2009 · Infection and immunity
[Show abstract][Hide abstract] ABSTRACT: The protective antigen (PA) component of the anthrax toxin (ATx) plays an essential role in the pathogenesis of the bioterrorism bacterium Bacillus anthracis. After oligomerization on the cell surface and docking of lethal factor and/or edema factor, PA is internalized and undergoes a conformational change when exposed to the low pH of the endosome to form a membrane-penetrating pore. While the structure of the PA prepore has been determined, precise structural information regarding the pore state remains lacking. Oxidative protein footprinting (OPF) can provide dynamic structural information about a protein complex through analysis of amino acid oxidation both before and after a conformational change. In this study, PA at pH 7.5 and 5.5 was exposed to hydroxyl radicals generated by ionizing radiation. Mass spectrometry was then used to both identify and quantitate the extent of oxidation of differentially modified residues. Several residues were found to be more readily oxidized at pH 7.5, most of which clustered toward the bottom plane of the prepore heptamer. Two amino acids had greater oxidation rates at pH 5.5, both found on the outer periphery of the prepore. When the OPF results were mapped to a current computational model of the pore, the accessibilities of some residues were consistent with their modeled positions in the pore (i.e., Y688 and V619/I620), while data for other residues (W346 and M350) appeared to conflict with the model. The results from this study illustrate the utility of OPF in generating empirical structural information for yet undetermined structures and offering opportunities for refinement for models thereof.
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin (CPE) causes the symptoms of a very common food poisoning. To assess whether CPE-induced cytotoxicity is necessary
for enterotoxicity, a rabbit ileal loop model was used to compare the in vivo effects of native CPE or recombinant CPE (rCPE),
both of which are cytotoxic, with those of the noncytotoxic rCPE variants rCPE D48A and rCPE168-319. Both CPE and rCPE elicited significant fluid accumulation in rabbit ileal loops, along with severe mucosal damage that starts
at villus tips and then progressively affects the entire villus, including necrosis of epithelium and lamina propria, villus
blunting and fusion, and transmural edema and hemorrhage. Similar treatment of ileal loops with either of the noncytotoxic
rCPE variants produced no visible histologic damage or fluid transport changes. Immunohistochemistry revealed strong CPE or
rCPE168-319 binding to villus tips, which correlated with the abundant presence of claudin-4, a known CPE receptor, in this villus region.
These results support (i) cytotoxicity being necessary for CPE-induced enterotoxicity, (ii) the CPE sensitivity of villus
tips being at least partially attributable to the abundant presence of receptors in this villus region, and (iii) claudin-4
being an important intestinal receptor for CPE. Finally, rCPE168-319 was able to partially inhibit CPE-induced histologic damage, suggesting that noncytotoxic rCPE variants might be useful for
protecting against some intestinal effects of CPE.
Preview · Article · Sep 2008 · Infection and immunity
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin is a common cause of food-borne and antibiotic-associated diarrhea. The toxin's receptors on intestinal epithelial cells include claudin-3 and -4, members of a large family of tight junction proteins. Toxin-induced cytolytic pore formation requires residues in the NH(2)-terminal half, whereas residues near the COOH terminus are required for binding to claudins. The claudin-binding COOH-terminal domain is not toxic and is currently under investigation as a potential drug absorption enhancer. Because claudin-4 is overexpressed on some human cancers, the toxin is also being investigated for targeting chemotherapy. Our aim was to solve the structure of the claudin-binding domain to advance its therapeutic applications. The structure of a 14-kDa fragment containing residues 194 to the native COOH terminus at position 319 was solved by x-ray diffraction to a resolution of 1.75A. The structure is a nine-strand beta sandwich with previously unappreciated similarity to the receptor-binding domains of several other toxins of spore-forming bacteria, including the collagen-binding domain of ColG from Clostridium histolyticum and the large Cry family of toxins (including Cry4Ba) of Bacillus thuringiensis. Correlations with previous studies suggest that the claudin-4 binding site is on a large surface loop between strands beta8 and beta9 or includes these strands. The sequence that was crystallized (residues 194-319) binds to purified human claudin-4 with a 1:1 stoichiometry and affinity in the submicromolar range similar to that observed for binding of native toxin to cells. Our results provide a structural framework to advance therapeutic applications of the toxin and suggest a common ancestor for several receptor-binding domains of bacterial toxins.
Preview · Article · Feb 2008 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin (CPE) binds to host cell receptors, forming a small complex precursor for two large complexes reportedly having molecular masses of approximately 155 or approximately 200 kDa. Formation of the approximately 155 kDa complex causes a Ca(2+) influx that leads to apoptosis or oncosis. CPE complex composition is currently poorly understood, although occludin was identified in the approximately 200 kDa complex. The current study used heteromer gel shift analysis to show both CPE large complexes contain six CPE molecules. Ferguson plots and size exclusion chromatography re-sized the approximately 155 and approximately 200 kDa complexes as approximately 425-500 kDa and approximately 550-660 kDa respectively. Co-immunoprecipitation and electroelution studies demonstrated both CPE-binding and non-CPE-binding claudins are associated with all three CPE complexes in Caco-2 cells and with small complex and approximately 425-500 kDa complex of claudin 4 transfectants. Fibroblast transfectants expressing claudin 4 or C-terminal truncated claudin 4 were CPE-sensitive and formed the approximately 425 kDa complex, indicating claudin-induced cell signalling is not required for CPE action and that expression of a single receptor claudin suffices for approximately 425-500 kDa CPE complex formation. These results identify CPE as a unique toxin that combines with tight junction proteins to form high-molecular-mass hexameric pores and alter membrane permeability.
Preview · Article · Dec 2007 · Cellular Microbiology
[Show abstract][Hide abstract] ABSTRACT: Brain metastasis is the most commonly occurring intracranial tumor whose incidence seems to be increasing. With standard therapy, the average survival time of patients is approximately 8 months, and treatment often leads to neurologic dysfunction in long-term survivors, emphasizing the need for novel therapeutics. Clostridium perfringens enterotoxin (CPE) has recently been shown to rapidly and specifically destroy cancer cells expressing CPE receptors claudin-3 and claudin-4. Unfortunately, the utility of CPE is precluded by systemic toxicity because its receptors are expressed in numerous organs. Here, we provide the first preclinical evidence that CPE may be uniquely suited to the local treatment of brain metastasis. By immunohistochemical analysis, claudin-3 and claudin-4 were expressed frequently in metastases from breast (15 of 18), lung (15 of 20), and colon (12 of 14) carcinoma, and infrequently in metastases from renal cell carcinoma (2 of 16) and melanoma (2 of 16). In contrast, expression of claudin-3 and claudin-4 was absent in adjacent normal brain tissue. Further examination of the central nervous system (CNS) revealed low or undetectable levels of claudin-3 and claudin-4 in all regions tested by Western and immunohistochemical analysis. Treatment of breast cancer cell lines (MCF-7, MDA-MB-468, NT2.5-luc) and normal human astrocytes with CPE in vitro resulted in rapid and dose-dependent cytolysis exclusively in breast cancer cells, correlating with claudin-3 and claudin-4 expression. Moreover, intracranial CPE treatment significantly inhibited tumor growth and increased survival in two murine models of breast cancer brain metastasis, without any apparent local or systemic toxicity. These data suggest that CPE therapy may have efficacy against a wide variety of brain metastases without CNS toxicity.
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin (CPE) is the etiological agent of the third most common food-borne illness in the United States. The enteropathogenic effects of CPE result from formation of large CPE-containing complexes in eukaryotic cell membranes. Formation of these approximately 155- and approximately 200-kDa complexes coincides with plasma membrane permeability changes in eukaryotic cells, causing a Ca2+ influx that drives cell death pathways. CPE contains a stretch of amino acids (residues 81 to 106) that alternates markedly in side chain polarity (a pattern shared by the transmembrane domains of the beta-barrel pore-forming toxin family). The goal of this study, therefore, was to investigate whether this CPE region is involved in pore formation. Complete deletion of the CPE region from 81 to 106 produced a CPE variant that was noncytotoxic for Caco-2 cells and was unable to form CPE pores. However, this variant maintained the ability to form the approximately 155-kDa large complex. This large complex appears to be a prepore present on the plasma membrane surface since it showed greater susceptibility to proteases, increased complex instability, and a higher degree of dissociation from membranes compared to the large complex formed by recombinant CPE. When a D48A mutation was engineered into this prepore-forming CPE variant, the resultant variant was unable to form any prepore approximately 155-kDa large complex. Collectively these findings reveal a new step in CPE action, whereby receptor binding is followed by formation of a prepore large complex, which then inserts into membranes to form a pore.
Preview · Article · Jun 2007 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Claudin-4, a tight junction (TJ) protein and receptor for the C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE), is overexpressed in epithelial ovarian cancer (EOC). Previous research suggests DNA methylation is a mechanism for claudin-4 overexpression in cancer and that C-CPE acts as an absorption-enhancing agent in claudin-4-expressing cells. We sought to correlate claudin-4 overexpression in EOC with clinical outcomes and TJ barrier function, investigate DNA methylation as a mechanism for overexpression, and evaluate the effect of C-CPE on the TJ.
Claudin-4 expression in EOC was quantified and correlated with clinical outcomes. Claudin-4 methylation status was determined, and claudin-4-negative cell lines were treated with a demethylating agent. Electric cell-substrate impedance sensing was used to calculate junctional (paracellular) resistance (Rb) in EOC cells after claudin-4 silencing and after C-CPE treatment.
Claudin-4 overexpression in EOC does not correlate with survival or other clinical endpoints and is associated with hypomethylation. Claudin-4 overexpression correlates with Rb and C-CPE treatment of EOC cells significantly decreased Rb in a dose- and claudin-4-dependent noncytotoxic manner.
C-CPE treatment of EOC cells leads to altered TJ function. Further research is needed to determine the potential clinical applications of C-CPE in EOC drug delivery strategies.
Full-text · Article · May 2007 · Neoplasia (New York, N.Y.)
[Show abstract][Hide abstract] ABSTRACT: The opportunistic pathogen Pseudomonas aeruginosa is a leading cause of nosocomial pneumonia. Among its virulence factors, the type IV pili of P. aeruginosa strain 1244 contain a covalently linked, three-sugar glycan of previously unknown significance. The work described in this
paper was carried out to determine the influence of the P. aeruginosa 1244 pilin glycan on pilus function, as well as a possible role in pathogenesis. To accomplish this, a deletion was introduced
into the pilO gene of this organism. The isogenic knockout strain produced, 1244G7, was unable to glycosylate pilin but could produce pili
normal in appearance and quantity. In addition, this strain had somewhat reduced twitching motility, was sensitive to pilus-specific
bacteriophages, and could form a normal biofilm. Analysis of whole cells and isolated pili from wild-type P. aeruginosa strain 1244 by transmission electron microscopy with a glycan-specific immunogold label showed that this saccharide was distributed
evenly over the fiber surface. The presence of the pilin glycan reduced the hydrophobicity of purified pili as well as whole
cells. With regard to pathogenicity, P. aeruginosa strains producing glycosylated pili were commonly found among clinical isolates and particularly among those strains isolated
from sputum. Competition index analysis using a mouse respiratory model comparing strains 1244 and 1244G7 indicated that the
presence of the pilin glycan allowed for significantly greater survival in the lung environment. These results collectively
suggest that the pilin glycan is a significant virulence factor and may aid in the establishment of infection.
Full-text · Article · Jan 2006 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Clostridium perfringens enterotoxin (CPE) has a unique mechanism of action that results in the formation of large, sodium dodecyl sulfate-resistant complexes involving tight junction proteins; those complexes then induce plasma membrane permeability alterations in host intestinal epithelial cells, leading to cell death and epithelial desquamation. Previous deletion and point mutational studies mapped CPE receptor binding activity to the toxin's extreme C terminus. Those earlier analyses also determined that an N-terminal CPE region between residues D45 and G53 is required for large complex formation and cytotoxicity. To more finely map this N-terminal cytotoxicity region, site-directed mutagenesis was performed with recombinant CPE (rCPE). Alanine-scanning mutagenesis produced one rCPE variant, D48A, that failed to form large complexes or induce cytotoxicity, despite having normal ability to bind and form the small complex. Two saturation variants, D48E and D48N, also had a phenotype resembling that of the D48A variant, indicating that both size and charge are important at CPE residue 48. Another alanine substitution rCPE variant, I51A, was highly attenuated for large complex formation and cytotoxicity, but rCPE saturation variants I51L and I51V displayed a normal large complex formation and cytotoxicity phenotype. Collectively, these mutagenesis results identify a core CPE sequence extending from residues G47 to I51 that directly participates in large complex formation and cytotoxicity.
Preview · Article · Jan 2005 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Feb 2004 · Reviews of Physiology, Biochemistry and Pharmacology