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Secretion of Clostridium difficile toxins A and B requires the holin-like protein TcdE.

Govind R, Dupuy B - PLoS Pathog. (2012)

Bottom Line: A C. difficile tcdE mutant strain grew at the same rate as the wild-type strain, but accumulated a dramatically reduced amount of toxin proteins in the medium.In addition, TcdE did not overtly affect membrane integrity of C. difficile in the presence of TcdA/TcdB.TcdE appears to be the first example of a bacterial protein that releases toxins into the environment by a phage-like system.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire Pathogenèse des Bactéries Anaérobies, Institut Pasteur, Paris, France.

ABSTRACT
The pathogenesis of Clostridium difficile, the major cause of antibiotic-associated diarrhea, is mainly associated with the production and activities of two major toxins. In many bacteria, toxins are released into the extracellular environment via the general secretion pathways. C. difficile toxins A and B have no export signature and their secretion is not explainable by cell lysis, suggesting that they might be secreted by an unusual mechanism. The TcdE protein encoded within the C. difficile pathogenicity locus (PaLoc) has predicted structural features similar to those of bacteriophage holin proteins. During many types of phage infection, host lysis is driven by an endolysin that crosses the cytoplasmic membrane through a pore formed by holin oligomerization. We demonstrated that TcdE has a holin-like activity by functionally complementing a λ phage deprived of its holin. Similar to λ holin, TcdE expressed in Escherichia coli and C. difficile formed oligomers in the cytoplamic membrane. A C. difficile tcdE mutant strain grew at the same rate as the wild-type strain, but accumulated a dramatically reduced amount of toxin proteins in the medium. However, the complemented tcdE mutant released the toxins efficiently. There was no difference in the abundance of tcdA and tcdB transcripts or of several cytoplasmic proteins in the mutant and the wild-type strains. In addition, TcdE did not overtly affect membrane integrity of C. difficile in the presence of TcdA/TcdB. Thus, TcdE acts as a holin-like protein to facilitate the release of C. difficile toxins to the extracellular environment, but, unlike the phage holins, does not cause the non-specific release of cytosolic contents. TcdE appears to be the first example of a bacterial protein that releases toxins into the environment by a phage-like system.

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PaLoc in C. difficile.A. Schematic diagram of PaLoc in toxigenic C. difficile strains. In non-toxigenic strains this region is replaced by a short 115 bp sequence. Arrows indicates the positive regulation of tcdR, tcdB and tcdA by σTcdR. B Predicted topology of TcdE and. λS holin Horizontal black bars represent the relative position of Cys 51 in S105 and Cys 29, 56, 79, 111 and 113 in TcdE.
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ppat-1002727-g001: PaLoc in C. difficile.A. Schematic diagram of PaLoc in toxigenic C. difficile strains. In non-toxigenic strains this region is replaced by a short 115 bp sequence. Arrows indicates the positive regulation of tcdR, tcdB and tcdA by σTcdR. B Predicted topology of TcdE and. λS holin Horizontal black bars represent the relative position of Cys 51 in S105 and Cys 29, 56, 79, 111 and 113 in TcdE.

Mentions: The toxin genes tcdA and tcdB lie within a chromosomal region of 19.6 kb designated the pathogenicity locus (PaLoc) (Figure 1A). The same locus encodes TcdR, an alternative sigma factor that specifically directs transcription from the toxin promoters as well as its own promoter, TcdC, an antagonist of TcdR that prevents the formation of the TcdR-containing RNA polymerase holoenzyme [12], [15], [16], and TcdE, whose function was not known.


Secretion of Clostridium difficile toxins A and B requires the holin-like protein TcdE.

Govind R, Dupuy B - PLoS Pathog. (2012)

PaLoc in C. difficile.A. Schematic diagram of PaLoc in toxigenic C. difficile strains. In non-toxigenic strains this region is replaced by a short 115 bp sequence. Arrows indicates the positive regulation of tcdR, tcdB and tcdA by σTcdR. B Predicted topology of TcdE and. λS holin Horizontal black bars represent the relative position of Cys 51 in S105 and Cys 29, 56, 79, 111 and 113 in TcdE.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369941&req=5

ppat-1002727-g001: PaLoc in C. difficile.A. Schematic diagram of PaLoc in toxigenic C. difficile strains. In non-toxigenic strains this region is replaced by a short 115 bp sequence. Arrows indicates the positive regulation of tcdR, tcdB and tcdA by σTcdR. B Predicted topology of TcdE and. λS holin Horizontal black bars represent the relative position of Cys 51 in S105 and Cys 29, 56, 79, 111 and 113 in TcdE.
Mentions: The toxin genes tcdA and tcdB lie within a chromosomal region of 19.6 kb designated the pathogenicity locus (PaLoc) (Figure 1A). The same locus encodes TcdR, an alternative sigma factor that specifically directs transcription from the toxin promoters as well as its own promoter, TcdC, an antagonist of TcdR that prevents the formation of the TcdR-containing RNA polymerase holoenzyme [12], [15], [16], and TcdE, whose function was not known.

Bottom Line: A C. difficile tcdE mutant strain grew at the same rate as the wild-type strain, but accumulated a dramatically reduced amount of toxin proteins in the medium.In addition, TcdE did not overtly affect membrane integrity of C. difficile in the presence of TcdA/TcdB.TcdE appears to be the first example of a bacterial protein that releases toxins into the environment by a phage-like system.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire Pathogenèse des Bactéries Anaérobies, Institut Pasteur, Paris, France.

ABSTRACT
The pathogenesis of Clostridium difficile, the major cause of antibiotic-associated diarrhea, is mainly associated with the production and activities of two major toxins. In many bacteria, toxins are released into the extracellular environment via the general secretion pathways. C. difficile toxins A and B have no export signature and their secretion is not explainable by cell lysis, suggesting that they might be secreted by an unusual mechanism. The TcdE protein encoded within the C. difficile pathogenicity locus (PaLoc) has predicted structural features similar to those of bacteriophage holin proteins. During many types of phage infection, host lysis is driven by an endolysin that crosses the cytoplasmic membrane through a pore formed by holin oligomerization. We demonstrated that TcdE has a holin-like activity by functionally complementing a λ phage deprived of its holin. Similar to λ holin, TcdE expressed in Escherichia coli and C. difficile formed oligomers in the cytoplamic membrane. A C. difficile tcdE mutant strain grew at the same rate as the wild-type strain, but accumulated a dramatically reduced amount of toxin proteins in the medium. However, the complemented tcdE mutant released the toxins efficiently. There was no difference in the abundance of tcdA and tcdB transcripts or of several cytoplasmic proteins in the mutant and the wild-type strains. In addition, TcdE did not overtly affect membrane integrity of C. difficile in the presence of TcdA/TcdB. Thus, TcdE acts as a holin-like protein to facilitate the release of C. difficile toxins to the extracellular environment, but, unlike the phage holins, does not cause the non-specific release of cytosolic contents. TcdE appears to be the first example of a bacterial protein that releases toxins into the environment by a phage-like system.

Show MeSH
Related in: MedlinePlus