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'''Unreleased structure'''


The entry 9ohf is ON HOLD  until Paper Publication
==CryoEM structure of apo Toxin B (TcdB) from Clostridioides difficile in the open CROP state==
<StructureSection load='9ohf' size='340' side='right'caption='[[9ohf]], [[Resolution|resolution]] 3.19&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[9ohf]] is a 1 chain structure with sequence from [https://en.wikipedia.org/wiki/Clostridioides_difficile Clostridioides difficile]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=9OHF OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=9OHF FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Electron Microscopy, [[Resolution|Resolution]] 3.19&#8491;</td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=9ohf FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=9ohf OCA], [https://pdbe.org/9ohf PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=9ohf RCSB], [https://www.ebi.ac.uk/pdbsum/9ohf PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=9ohf ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/TCDB_CLODI TCDB_CLODI] Precursor of a cytotoxin that targets and disrupts the colonic epithelium, inducing the host inflammatory and innate immune responses and resulting in diarrhea and pseudomembranous colitis (PubMed:20844489, PubMed:24919149). TcdB constitutes the main toxin that mediates the pathology of C.difficile infection, an opportunistic pathogen that colonizes the colon when the normal gut microbiome is disrupted (PubMed:19252482, PubMed:20844489). Compared to TcdA, TcdB is more virulent and more important for inducing the host inflammatory and innate immune responses (PubMed:19252482, PubMed:24919149). This form constitutes the precursor of the toxin: it enters into host cells and mediates autoprocessing to release the active toxin (Glucosyltransferase TcdB) into the host cytosol (PubMed:10768933, PubMed:11152463, PubMed:12941936, PubMed:17334356, PubMed:20498856). Targets colonic epithelia by binding to the frizzled receptors FZD1, FZD2 and FZD7, and enters host cells via clathrin-mediated endocytosis (PubMed:27680706). Frizzled receptors constitute the major host receptors in the colonic epithelium, but other receptors, such as CSPG4 or NECTIN3/PVRL3, have been identified (PubMed:25547119, PubMed:26038560, PubMed:27680706). Binding to carbohydrates and sulfated glycosaminoglycans on host cell surface also contribute to entry into cells (By similarity). Once entered into host cells, acidification in the endosome promotes the membrane insertion of the translocation region and formation of a pore, leading to translocation of the GT44 and peptidase C80 domains across the endosomal membrane (PubMed:11152463, PubMed:12941936, PubMed:24567384). This activates the peptidase C80 domain and autocatalytic processing, releasing the N-terminal part (Glucosyltransferase TcdB), which constitutes the active part of the toxin, in the cytosol (PubMed:17334356, PubMed:27571750).[UniProtKB:P16154]<ref>PMID:10768933</ref> <ref>PMID:11152463</ref> <ref>PMID:12941936</ref> <ref>PMID:17334356</ref> <ref>PMID:19252482</ref> <ref>PMID:20498856</ref> <ref>PMID:20844489</ref> <ref>PMID:24567384</ref> <ref>PMID:24919149</ref> <ref>PMID:25547119</ref> <ref>PMID:26038560</ref> <ref>PMID:27571750</ref> <ref>PMID:27680706</ref>  Active form of the toxin, which is released into the host cytosol following autoprocessing and inactivates small GTPases (PubMed:16157585, PubMed:17901056, PubMed:24905543, PubMed:24919149, PubMed:7777059, PubMed:8144660). Acts by mediating monoglucosylation of small GTPases of the Rho family (Rac1, RhoA, RhoB, RhoC, RhoG and Cdc42) in host cells at the conserved threonine residue located in the switch I region ('Thr-37/35'), using UDP-alpha-D-glucose as the sugar donor (PubMed:16157585, PubMed:17901056, PubMed:24905543, PubMed:24919149, PubMed:7777059). Monoglucosylation of host small GTPases completely prevents the recognition of the downstream effector, blocking the GTPases in their inactive form, leading to actin cytoskeleton disruption and cell death, resulting in the loss of colonic epithelial barrier function (PubMed:24919149, PubMed:7777059).<ref>PMID:16157585</ref> <ref>PMID:17901056</ref> <ref>PMID:24905543</ref> <ref>PMID:24919149</ref> <ref>PMID:7777059</ref> <ref>PMID:8144660</ref>
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
Intestinal bile acids are a family of host and microbiota metabolites that can directly inhibit toxin B (TcdB), the primary virulence factor of Clostridioides difficile that causes infectious diarrhoea and colitis. However, the mechanism underlying the inhibition is unclear. Here we used cryogenic electron microscopy and determined the structure of TcdB bound to inhibitory bile acids cholic acid (methyl ester) and taurochenodeoxycholic acid at 2.9 A and 3.3 A resolution, respectively. These structures revealed that bile acids lock the C-terminal CROP domain of TcdB in a conformation that allosterically masks the two receptor-binding sites and prevents target cell recognition. Guided by the structure, we synthesized gut-restricted bile acid derivatives, designed to evade the bile acid reuptake transporters within the gut. One of the derivatives, sBA-2, was retained within the gut upon oral dosing and protected mice from toxin-induced C. difficile disease pathology. Our study uncovers the structural basis of inhibition of TcdB by bile acids and its analogues, paving the way for the development of orally deliverable therapeutics against C. difficile.


Authors: Miletic, S., Li, Z., Melnyk, R.A.
Structure-guided design of a synthetic bile acid that inhibits Clostridioides difficile TcdB toxin.,Miletic S, Icho S, Li Z, Tam J, Rose EC, Perkins CE, Nakhi A, Yang X, Hang HC, Rubinstein JL, Dosa PI, Theriot CM, Melnyk RA Nat Microbiol. 2025 Dec;10(12):3215-3228. doi: 10.1038/s41564-025-02179-1. Epub , 2025 Nov 18. PMID:41254394<ref>PMID:41254394</ref>


Description: CryoEM structure of apo Toxin B (TcdB) from Clostridioides difficile in the open CROP state
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
[[Category: Unreleased Structures]]
</div>
[[Category: Melnyk, R.A]]
<div class="pdbe-citations 9ohf" style="background-color:#fffaf0;"></div>
[[Category: Li, Z]]
== References ==
[[Category: Miletic, S]]
<references/>
__TOC__
</StructureSection>
[[Category: Clostridioides difficile]]
[[Category: Large Structures]]
[[Category: Li Z]]
[[Category: Melnyk RA]]
[[Category: Miletic S]]
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