| 1.C.59 The Clostridium perfringens Enterotoxin (CPE) Family
C. perfringens uses an arsenal of 14 toxins to cause enteric and histotoxic infections in humans and domestic animals. One of these is CPE, also called heat-labile enterotoxin B chain precursor, possibly the most important of them from a medical standpoint. It forms complexes of variable sizes (~135, 155 and 200 kDa), but the 155 kDa complex alone causes 86Rb+ release and is probably responsible for the diarrheal and cramping symptoms of C. perfringens type A food poisoning. CPE also prevents tight junction formation, possibly by complexing the tight junction structural protein, occludin, in the 200 kDa complex. CPE is thus a bifunctional toxin which first generates pores (the 155 kDa complex) and then damages the tight junctions (the 200 kDa complex). It thus increases both cellular and paracellular permeability, thereby contributing to diarrhea of C. perfringens gastrointestinal disease. The Clostridium botulinum haemagglutinin/neurotoxin is 623 aas long (in contrast to CPE which is 309 aas long) and exhibits an internal repeat. Both repeats are about 24% identical to CPE. This toxin is composed of several subcomponents of ~53, 33, 23 and 17 kDa. Mature botulinum toxins are large and heterogeneous in size (Singh et al., 2001).
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. Briggs et al. (2011) 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. They show that CPE forms a trimer in both crystal forms, and that this trimer is likely to be biologically relevant, although it is not the active pore form. The crystal structure of Clostridium perfringens enterotoxin displays features of beta-pore-forming toxins (Kitadokoro et al., 2011).
The soluble monomer of the β-barrel pore-forming toxin (PFTs), Monalysin, is
cleaved to yield oligomeric pores. The structure of a cleaved form
lacking the transmembrane domain has been solved by x-ray crystalography
and cryo-EM (PDB#4MJT; Leone et al. 2015).
The structure displays an elongated shape, resembling those of
beta-pore-forming toxins such as
aerolysin, but it lacks the receptor binding domain. Pro-monalysin forms
a stable doughnut-like 18-mer complex
composed of two disk-shaped nonamers held together by N-terminal
swapping of the pro-peptides. This is in contrast with the monomeric
pro-form of the other beta-PFTs that are receptor-dependent for membrane interaction. The membrane-spanning region of
pro-monalysin is fully buried in
the center of the doughnut, suggesting that upon pro-peptide cleavage,
the two disk-shaped nonamers
can - and have to - dissociate to leave the transmembrane segments free
to deploy and lead to pore
formation. In contrast with other toxins, the delivery of 18 subunits at
once, nearby the cell
surface, may be used to by-pass the requirement for a receptor-dependent
concentration to reach the
threshold for oligomerization into the pore forming complex (Leone et al. 2015).
The transport reactions catalyzed by members of the CPE familly is:
small molecules (in)  small molecules (out)
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| References: |
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Benz, R. and M.R. Popoff. (2018). Enterotoxin: The Toxin Forms Highly Cation-Selective Channels in Lipid Bilayers. Toxins (Basel) 10:.
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Briggs, D.C., C.E. Naylor, J.G. Smedley, 3rd, N. Lukoyanova, S. Robertson, D.S. Moss, B.A. McClane, and A.K. Basak. (2011). Structure of the food-poisoning Clostridium perfringens enterotoxin reveals similarity to the aerolysin-like pore-forming toxins. J. Mol. Biol. 413: 138-149.
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Freedman, J.C., M.R. Hendricks, and B.A. McClane. (2017). The Potential Therapeutic Agent Mepacrine Protects Caco-2 Cells against Enterotoxin Action. mSphere 2:.
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Kitadokoro, K., K. Nishimura, S. Kamitani, A. Fukui-Miyazaki, H. Toshima, H. Abe, Y. Kamata, Y. Sugita-Konishi, S. Yamamoto, H. Karatani, and Y. Horiguchi. (2011). Crystal structure of Clostridium perfringens enterotoxin displays features of β-pore-forming toxins. J. Biol. Chem. 286: 19549-19555.
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Leone P., Bebeacua C., Opota O., Kellenberger C., Klaholz B., Orlov I., Cambillau C., Lemaitre B. and Roussel A. (2015). X-ray and Cryo-electron Microscopy Structures of Monalysin Pore-forming Toxin Reveal Multimerization of the Pro-form. J Biol Chem. 290(21):13191-201.
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Pahle, J., J. Aumann, D. Kobelt, and W. Walther. (2015). Oncoleaking: Use of the Pore-Forming Clostridium perfringens Enterotoxin (CPE) for Suicide Gene Therapy. Methods Mol Biol 1317: 69-85.
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Singh, U., L.L. Mitic, E.U. Wieckowski, J.M. Anderson and B.A. McClane (2001). Comparative biochemical and immunocytochemical studies reveal differences in the effects of Clostridium perfringens enterotoxin on polarized CaCo-2 cells versus vero cells. J. Biol. Chem. 276: 33402-33412.
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Veshnyakova, A., J. Protze, J. Rossa, I.E. Blasig, G. Krause, and J. Piontek. (2010). On the Interaction of Clostridium perfringens Enterotoxin with Claudins. Toxins (Basel) 2: 1336-1356.
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Walther, W., S. Petkov, O.N. Kuvardina, J. Aumann, D. Kobelt, I. Fichtner, M. Lemm, J. Piontek, I.E. Blasig, U. Stein, and P.M. Schlag. (2012). Novel Clostridium perfringens enterotoxin suicide gene therapy for selective treatment of claudin-3- and -4-overexpressing tumors. Gene Ther 19: 494-503.
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.C.59.1.1 | CPE (Clostridium perfringens Enterotoxin) has been used for suicide gene therapy for selective treatment of claudin-3-and-4-overexpressing tumors (Walther et al., 2011). It can be used as an oncoleaking/tumor eradication agent as this pore-forming protein exerts specific and rapid toxicity towards claudin-3- and -4-overexpressing cancers (Pahle et al. 2015). The crystal structure of Clostridium perfringens enterotoxin displays features of beta-pore-forming toxins (Kitadokoro et al., 2011). The N-terminal region (nCPE) mediates the cytotoxic effect through pore formation in the plasma membrane of the mammalian host cell. The C-terminal region (cCPE) binds to the second extracellular loop of a subset of claudins, Claudin-3 and claudin-4, with high affinity (Veshnyakova et al., 2010). cCPE is not cytotoxic but is a potent modulator of tight junctions. The toxin forms highly cation-selective channels in lipid bilayers (Benz and Popoff 2018). Mepacrine inhibits CPE-induced electrophysiology effects in artificial lipid bilayers lacking CPE receptors by blocking subunit oligomerization and pore formation (Freedman et al. 2017). | Bacteria; Firmicutes | Enterotoxin of Clostridium perfringens (P01558) |
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| 1.C.59.1.2 | Enterotoxin of 703 aas | | Enterotoxin of Clostridium massiliamazoniense |
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.C.59.2.1 | Neurotoxin of 623 aa | Clostridial species | Haemagglutinin/neurotoxin precursor of Clostridium botulinum (P46085) |
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| 1.C.59.2.2 | Enterotoxin of 625 aas | | Enterotoxin of Clostridium cuniculi |
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| 1.C.59.2.3 | Botulinum neurotoxin hemagglutinin HA70 subunit of 629 aas | | HA70 of Clostridium argentinense |
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.C.59.3.1 | The β-barrel pore-forming toxin (PFP), Monalysin. The soluble monomer is cleaved to yield oligomeric pores. The structure of a cleaved form lacking the transmembrane domain has been solved by x-ray crystalography and cryo-EM (PDB#4MJT; Leone et al. 2015). The structure displays an elongated shape, resembling those of beta-pore-forming toxins such as
aerolysin, but it lacks the receptor binding domain. Pro-monalysin forms a stable doughnut-like 18-mer complex
composed of two disk-shaped nonamers held together by N-terminal swapping of the pro-peptides. This is in contrast with the monomeric pro-form of the other beta-PFTs that are receptor-dependent for membrane interaction. The membrane-spanning region of pro-monalysin is fully buried in
the center of the doughnut, suggesting that upon pro-peptide cleavage, the two disk-shaped nonamers
can - and have to - dissociate to leave the transmembrane segments free to deploy and lead to pore
formation. In contrast with other toxins, the delivery of 18 subunits at once, nearby the cell
surface, may be used to by-pass the requirement for a receptor-dependent concentration to reach the
threshold for oligomerization into the pore-forming complex (Leone et al. 2015). | Proteobacteria | Monalysin of Pseudomonas entomophila (pathogen of Drosophila) |
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| 1.C.59.3.2 | Monalysin homologue of 245 aas | Proteobacteria | Monalysin homologue of Pseudomonas putida |
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| 1.C.59.3.3 | Putative toxin of 264 aas | Proteobacteria | Putative toxin of Cystobacter fuscus |
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.C.59.4.1 | Putative toxin, SmlA of 283 aas. Deleting the encoding gene gives rise to slime molds that can only form small aggregates. May regulate the secretion or processing of a secreted factor that regulates aggregate size.
| Amoebozoa; Mecetozoa
| SmlA of Dictyostelium discoideum (Slime mold) |
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| 1.C.59.4.2 | Uncharacterized protein of250 aas |
Amoebozoa; Mycetoza
| UP of Dictyostelium discoideum (Slime mold) |
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| 1.C.59.4.3 | Uncharacterized protein of 271 aas, SmlA | Amoebozoa (Mycetozoa) | UP of Polysphondylium pallidum (Cellular slime mold) |
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| 1.C.59.4.4 | Uncharacterized protein of 324 aas | | UP of Cavenderia fasciculata (Slime mold) (Dictyostelium fasciculatum) |
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| Examples: |
| TC# | Name | Organismal Type | Example |
| 1.C.59.5.1 | uncharacterized protein of 408 aas, DwiI. | | DwiI of Drosophila willistoni (Fruit fly) |
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| 1.C.59.5.2 | DUF1679 domain-containing protein of 354 aas | | DUF1679 ptotein of Henriciella litoralis |
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| 1.C.59.5.3 | Uncharacterized protein of 677 aas. | | UP of Mycobacterium marinum |
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| 1.C.59.5.4 | DUF1679 domain-containing protein of 488 aa | | DUF1679 protein of Sphingomonas panacis |
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| 1.C.59.5.5 | Uncharacterized protein of 414 aas | | UP of Trichuris suis |
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| 1.C.59.5.6 | DUF1679 domain-containing protein of 323 aa | | DUF1679 protein of Cyclobacterium amurskyense |
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| 1.C.59.5.7 | Uncharacterized protein of 418 aas | | UP of Zeugodacus cucurbitae (melon fly) |
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| 1.C.59.5.8 | Uncharacterized protein of 428 aas | | UP of Cimex lectularius |
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| 1.C.59.5.9 | Aminoglycoside phosphotransferase family protein of 330 aa | | AGPase of Deinococcus ficus |
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