title: Evidence for dual receptor-binding sites in Clostridium difficile toxin A.
abstract: TcdA (308 kDa) and TcdB (270 kDa) disrupt the integrity of the intestinal epithelial barrier and provide an environment favorable for Clostridium difficile colonization. Recent evidence suggests that entry of TcdA into cells is mediated by at least two domains. Here, we report the characterization of a second receptor-binding domain (RBD2) for TcdA. While both the isolated combined repetitive oligopeptides (CROPs) and RBD2 fragments are rapidly internalized into cells under physiologic conditions, only the CROPs domain appreciably accumulates at the cell surface. Once internalized, CROPs and RBD2 are trafficked to late endosomal compartments. An internal deletion of RBD2 from TcdA holotoxin ablated toxicity in HT29 cells. These data are consistent with the recently proposed dual receptor model of cellular entry.
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO, USA.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Lambert
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Missouri School of Medicine, Columbia, MO, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Baldwin
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D001665:Binding Sites; D001692:Biological Transport; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D016360:Clostridioides difficile / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D004305:Dose-Response Relationship, Drug; D004768:Enterotoxins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D019073:HT29 Cells; D006801:Humans; D009842:Oligopeptides / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000633:toxicity
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; D009842:Oligopeptides; D011994:Recombinant Proteins; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile
keywords: 
  Clostridium difficile
  ; TcdA; receptor binding domain