Structure of the cell-binding component of the Clostridium difficile binary toxin reveals a di-heptamer macromolecular assembly

Authors

• Xingjian Xu, CUNY Advanced Science Research CenterFollow
• Raquel Godoy-Ruiz, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• Kaylin A. Adipietro, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• Christopher Peralta, CUNY Advanced Science Research Center
• Danya Ben-Hail, CUNY Advanced Science Research Center
• Kristeny M. Varney, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• Mary E. Cook, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• Braden M. Roth, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• Paul T. Wilder, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• Thomas Cleveland, National Institute of Standards
• Alexander Grishaev, National Institute of Standards
• Heather M. Neu, University of Maryland School of Pharmacy
• Sarah L. J. Michel, University of Maryland School of Pharmacy
• Wenbo Yu, Institute for Bioscience and Biotechnology Research, University of Maryland
• Dorothy Beckett, Department of Chemistry & Biochemistry, University of Maryland
• Richard R. Rustand, Merck & Co., Inc.
• Catherine Lancaster, Merck & Co., Inc.
• John W. Loughney, Merck & Co., Inc.
• Adam Kristopeit, Merck & Co., Inc.
• Sianny Christantii, Merck & Co., Inc.
• Jessica W. Olson, Merck & Co., Inc.
• Alexander D. MacKerell, Institute for Bioscience and Biotechnology Research, University of Maryland
• Amedee des Georges, CUNY Advanced Science Research CenterFollow
• Edwin Pozharski, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine
• David J. Weber, Department of Biochemistry & Molecular Biology, University of Maryland School of Medicine

Document Type

Article

Publication Date

1-14-2020

Abstract

Targeting Clostridium difficile infection is challenging because treatment options are limited, and high recurrence rates are common. One reason for this is that hypervirulent C. difficile strains often have a binary toxin termed the C. difficile toxin, in addition to the enterotoxins TsdA and TsdB. The C. difficile toxin has an enzymatic component, termed CDTa, and a pore-forming or delivery subunit termed CDTb. CDTb was characterized here using a combination of singleparticle cryoelectron microscopy, X-ray crystallography, NMR, and other biophysical methods. In the absence of CDTa, 2 di-heptamer structures for activated CDTb (1.0 MDa) were solved at atomic resolution, including a symmetric (^SymCDTb; 3.14 Å) and an asymmetric form (^AsymCDTb; 2.84 Å). Roles played by 2 receptor-binding domains of activated CDTb were of particular interest since the receptorbinding domain 1 lacks sequence homology to any other known toxin, and the receptor-binding domain 2 is completely absent in other well-studied heptameric toxins (i.e., anthrax). For ^AsymCDTb, a Ca²⁺ binding site was discovered in the first receptor-binding domain that is important for its stability, and the second receptor-binding domain was found to be critical for host cell toxicity and the diheptamer fold for both forms of activated CDTb. Together, these studies represent a starting point for developing structure-based drug-design strategies to target the most severe strains of C. difficile.

Comments

This article was originally published in PNAS, Proceedings of the National Academy of Sciences of the United States, available at https://doi.org/10.1073/pnas.1919490117

This work is distributed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0).