Recognition of Semaphorin Proteins by P. sordellii Lethal Toxin Reveals Principles of Receptor Specificity in Clostridial Toxins

Cell. 2020 Jul 23;182(2):345-356.e16. doi: 10.1016/j.cell.2020.06.005.

Hunsang Lee ¹, Greg L Beilhartz ², Iga Kucharska ², Swetha Raman ², Hong Cui ², Mandy Hiu Yi Lam ¹, Huazhu Liang ³, John L Rubinstein ⁴, Daniel Schramek ⁵, Jean-Philippe Julien ⁶, Roman A Melnyk ⁷, Mikko Taipale ⁸

Affiliations

1 Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1, Canada.
2 Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, ON M5G 0A4, Canada.
3 Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, ON M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada.
4 Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, ON M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 1L7, Canada.
5 Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada.
6 Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, ON M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada; Molecular Architecture of Life Program, Canadian Institute for Advanced Research (CIFAR), Toronto, ON M5G 1M1, Canada. Electronic address: [email protected].
7 Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto, ON M5G 0A4, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada. Electronic address: [email protected].
8 Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1, Canada; Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Molecular Architecture of Life Program, Canadian Institute for Advanced Research (CIFAR), Toronto, ON M5G 1M1, Canada. Electronic address: [email protected].

PMID: 32589945 DOI: 10.1016/j.cell.2020.06.005

Abstract

Pathogenic clostridial species secrete potent toxins that induce severe host tissue damage. Paeniclostridium sordellii lethal toxin (TcsL) causes an almost invariably lethal toxic shock syndrome associated with gynecological infections. TcsL is 87% similar to C. difficile TcdB, which enters host cells via Frizzled receptors in colon epithelium. However, P. sordellii infections target vascular endothelium, suggesting that TcsL exploits another receptor. Here, using CRISPR/Cas9 screening, we establish semaphorins SEMA6A and SEMA6B as TcsL receptors. We demonstrate that recombinant SEMA6A can protect mice from TcsL-induced edema. A 3.3 Å cryo-EM structure shows that TcsL binds SEMA6A with the same region that in TcdB binds structurally unrelated Frizzled. Remarkably, 15 mutations in this evolutionarily divergent surface are sufficient to switch binding specificity of TcsL to that of TcdB. Our findings establish semaphorins as physiologically relevant receptors for TcsL and reveal the molecular basis for the difference in tissue targeting and disease pathogenesis between highly related toxins.

Keywords

CRISPR/Cas9 screening; Clostridial toxins; P. sordellii; SEMA6A; SEMA6B; TcsL; bacterial exotoxins; cryo-EM; semaphorin.

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