| Structural highlights
Function
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][1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] Active form of the toxin, which is released into the host cytosol following autoprocessing and inactivates small GTPases (PubMed:8144660, PubMed:7777059, PubMed:16157585, PubMed:17901056, PubMed:24905543, PubMed:24919149). 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:7777059, PubMed:16157585, PubMed:17901056, PubMed:24905543, PubMed:24919149). 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:7777059, PubMed:24919149).[14] [15] [16] [17] [18] [19]
Publication Abstract from PubMed
Clostridium difficile causes life-threatening diarrhea and is the leading cause of healthcare-associated bacterial infections in the United States. TcdA and TcdB bacterial toxins are primary determinants of disease pathogenesis and are attractive therapeutic targets. TcdA and TcdB contain domains that use UDP-glucose to glucosylate and inactivate host Rho GTPases, resulting in cytoskeletal changes causing cell rounding and loss of intestinal integrity. Transition state analysis revealed glucocationic character for the TcdA and TcdB transition states. We identified transition state analogue inhibitors and characterized them by kinetic, thermodynamic and structural analysis. Iminosugars, isofagomine and noeuromycin mimic the transition state and inhibit both TcdA and TcdB by forming ternary complexes with Tcd and UDP, a product of the TcdA- and TcdB-catalyzed reactions. Both iminosugars prevent TcdA- and TcdB-induced cytotoxicity in cultured mammalian cells by preventing glucosylation of Rho GTPases. Iminosugar transition state analogues of the Tcd toxins show potential as therapeutics for C. difficile pathology.
Inhibition of Clostridium difficile TcdA and TcdB toxins with transition state analogues.,Paparella AS, Aboulache BL, Harijan RK, Potts KS, Tyler PC, Schramm VL Nat Commun. 2021 Nov 1;12(1):6285. doi: 10.1038/s41467-021-26580-6. PMID:34725358[20]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
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- ↑ Paparella AS, Aboulache BL, Harijan RK, Potts KS, Tyler PC, Schramm VL. Inhibition of Clostridium difficile TcdA and TcdB toxins with transition state analogues. Nat Commun. 2021 Nov 1;12(1):6285. PMID:34725358 doi:10.1038/s41467-021-26580-6
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