Lectin Activity of the TcdA and TcdB Toxins of Clostridium difficile.

Lauren E Hartley-Tassell,Milena M Awad,Christopher J Day,Maria Scarselli,Kate L Seib,Joe Tiralongo,Michael P Jennings,Silvana Savino,Dena Lyras

doi:10.1128/iai.00676-18

Abstract

Clostridium difficile is a major cause of hospital-acquired antibiotic-associated diarrhea. C. difficile produces two cytotoxins, TcdA and TcdB; both toxins are multidomain proteins that lead to cytotoxicity through the modification and inactivation of small GTPases of the Rho/Rac family. Previous studies have indicated that host glycans are targets for TcdA and TcdB, with interactions thought to be with both α- and β-linked galactose. In the current study, screening of glycan arrays with different domains of TcdA and TcdB revealed that the binding regions of both toxins interact with a wider range of host glycoconjugates than just terminal α- and β-linked galactose, including blood groups, Lewis antigens, N-acetylglucosamine, mannose, and glycosaminoglycans. The interactions of TcdA and TcdB with ABO blood group and Lewis antigens were assessed by surface plasmon resonance (SPR). The blood group A antigen was the highest-affinity ligand for both toxins. Free glycans alone or in combination were unable to abolish Vero cell cytotoxicity by TcdB. SPR competition assays indicate that there is more than one glycan binding site on TcdB. Host glycoconjugates are common targets of bacterial toxins, but typically this binding is to a specific structure or related structures. The binding of TcdA and TcdB is to a wide range of host glycans providing a wide range of target cells and tissues in vivo.

Highlights

Clostridium difficile is a major cause of hospital-acquired antibioticassociated diarrhea
C. difficile produces two major cytotoxins, TcdA and TcdB (TcdA/B), with TcdB thought to be largely responsible for the gut damage that occurs during Clostridium difficile infections (CDIs) [3, 4]
TcdA and TcdB are multidomain proteins that consist of at least four functionally distinct regions (A, C, D, and B) [7,8,9]. These include the glucosyltransferase domain (GTD) that is responsible for inactivating small Rho-dependent GTPases, the cysteine protease domain (CPD) required for proteolytic cleavage of the toxins, the delivery domain (DD) that enables the translocation of the N terminus of the proteins into the cell cytosol, and the receptor binding domain (RBD) that encodes the combined repetitive oligopeptide (CROP) structures, March 2019 Volume 87 Issue 3 e00676-18

Summary

Introduction

Clostridium difficile is a major cause of hospital-acquired antibioticassociated diarrhea. C. difficile produces two major cytotoxins, TcdA and TcdB (TcdA/B), with TcdB thought to be largely responsible for the gut damage that occurs during CDI [3, 4] Both toxins are monoglucosyltransferases that form part of the family of large clostridial toxins, or LCTs. Both toxins are monoglucosyltransferases that form part of the family of large clostridial toxins, or LCTs These toxins modify and inactivate small GTPases of the Rho/Rac family, leading to colonic inflammation, tissue damage, and cell death [5, 6]. As suggested by Schorch et al, all LCTs, including TcdB, are likely to use a similar binding mechanism to initiate host cell contact [13]

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