title: Structural basis for antibody recognition in the receptor-binding domains of toxins A and B from Clostridium difficile.
abstract: Clostridium difficile infection is a serious and highly prevalent nosocomial disease in which the two large, Rho-glucosylating toxins TcdA and TcdB are the main virulence factors. We report for the first time crystal structures revealing how neutralizing and non-neutralizing single-domain antibodies (sdAbs) recognize the receptor-binding domains (RBDs) of TcdA and TcdB. Surprisingly, the complexes formed by two neutralizing antibodies recognizing TcdA do not show direct interference with the previously identified carbohydrate-binding sites, suggesting that neutralization of toxin activity may be mediated by mechanisms distinct from steric blockage of receptor binding. A camelid sdAb complex also reveals the molecular structure of the TcdB RBD for the first time, facilitating the crystallization of a strongly negatively charged protein fragment that has resisted previous attempts at crystallization and structure determination. Electrospray ionization mass spectrometry measurements confirm the stoichiometries of sdAbs observed in the crystal structures. These studies indicate how key epitopes in the RBDs from TcdA and TcdB are recognized by sdAbs, providing molecular insights into toxin structure and function and providing for the first time a basis for the design of highly specific toxin-specific therapeutic and diagnostic agents.
authors: From the Department of Biological Sciences and Alberta Glycomics Centre, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors: Tomohiko
authors: T
authors: Murase
authors: Luiz
authors: L
authors: Eugenio
authors: Melissa
authors: M
authors: Schorr
authors: Greg
authors: G
authors: Hussack
authors: Jamshid
authors: J
authors: Tanha
authors: Elena N
authors: EN
authors: Kitova
authors: John S
authors: JS
authors: Klassen
authors: Kenneth K S
authors: KK
authors: Ng
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000737:chemistry* / Q000276:immunology; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D001427:Bacterial Toxins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D016360:Clostridioides difficile / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D018360:Crystallography, X-Ray; D004768:Enterotoxins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D006801:Humans; D017434:Protein Structure, Tertiary; D057127:Single-Chain Antibodies / Q000737:chemistry* / Q000276:immunology; D013329:Structure-Activity Relationship
chemical_list: D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004768:Enterotoxins; D000939:Epitopes; D057127:Single-Chain Antibodies; C041348:tcdA protein, Clostridium difficile; C031815:toxB protein, Clostridium difficile
keywords: Antibodies; Bacterial Toxins; Mass Spectrometry (MS); Protein-Protein Interactions; X-ray Crystallography