page_title: Clostridium difficile toxin B
section_title: Genetics
hierarchical_section_title: Clostridium difficile toxin B / Function / Genetics
caption_attribution_description: English: Figurerepresentsthelocus of 19.8 kb found in C.difficile strain 630, DSM 27543&#160;https://www.dsmz.de/collection/catalogue/details/culture/DSM-27543&#160;, GenBankaccessionnumberAM180355&#160;https://www.ncbi.nlm.nih.gov/nuccore/AM180355&#160;, positions 770.154 to 789.973 bp. Genes depicted (left to right, 5’-3’ downstreamforward) are: 1.&#160;tcdD pathogenicity locus conserved protein, coexpressed and found in several operons encoding toxins in other species, with DNA repair and recombination&#160; activityreportedin highlysimilar archaealpeptides and Sigma factor positive regulator.&#160; 2. tcdB&#160;Clostridium_difficile_toxin_A, a&#160;&#160;cytotoxin, a very important protein for virulence.&#160;3.&#160;tcdE, an&#160;Holin-like protein secretion function.&#160;4.&#160;tcdA,&#160;Clostridium_difficile_toxin_A , enterotoxin. 5. tcdC,&#160;putative peptide (coding reverse) and negative regulator. Toxin B and Toxin A have a similarity at the DNA level. They both a&#160;functional&#160;toxin&#160;protein of&#160;4 domains, encoded in glycosylating enzymatic domain A, autocatalytic processing domain cysteine protease C, translocating&#160;domain D and binding C-terminal domain B.&#160;&#160;The protein undergoes postransductional modifications and the domains act in synergic effect to achieve pathogenic effects in the cell targeting&#160;&#160;Rho family of GTPases https://en.wikipedia.org/wiki/Rho_family_of_GTPases&#160;. It must be noted that the loci composition has been found to be variable across different strains. There are clinical isolates not having a functional toxin A (pseudogene), or having a large transposon insertion between toxin A and toxin B, or not having any functional toxin gene. Also there are strains having differences in the 5' regulator, having a pseudogene or small accessory&#160;genes.
context_page_description: Clostridium difficile toxin B is a cytotoxin produced by the bacteria Clostridium difficile. It is one of two major kinds of toxins produced by C. difficile, the other being an enterotoxin. Both are very potent and lethal.
context_section_description: The gene that encodes the TcdB protein, tcdB, is located within the chromosomal region of 19.6 kb. This is known as the locus of pathogenicity or PaLoc (Figure 2). The open reading frame (ORF) for tcdB is 7,098 nucleotides in length. It is important to mention that—besides the major toxin genes in the PaLoc region—there are three other accessory genes that encode in the PaLoc region: tcdR (L), tcdC (R) and tcdE in the middle. These genes help to regulate TcdA and TcdB expression. They also help to secrete or release the toxins from the cell. The encoding gene tcdE, located between tcdB and tcdA, is analogous to holin proteins, thus, it is suggested that tcdE works as a facilitator gene that enhances the release or secretion of TcdA and TcdB consequently increasing the permeability of the host cell membrane.
caption: Figure 2: Archetypical Pathogenicity Locus (PaLoc),encoding the large clostridial toxins(LCTs) involved in C. difficile infections CDI.
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