The chaperonin TRiC/CCT is essential for the action of bacterial glycosylating protein toxins like Clostridium difficile toxins A and B Marcus Steinemanna,b, Andreas Schlosserc, Thomas Janka,1, and Klaus Aktoriesa,d,1 aInstitute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; bFaculty of Biology, University of Freiburg, 79104 Freiburg, Germany; cRudolf Virchow Center for Experimental Biomedicine, University of Würzburg, 97080 Würzburg, Germany; and dCenter for Biological Signaling Studies, University of Freiburg, 79104 Freiburg, Germany Edited by F. Ulrich Hartl, Max Planck Institute of Biochemistry, Martinsried, Germany, and approved August 8, 2018 (received for review May 3, 2018) Various bacterial protein toxins, including Clostridium difficile tox- however, how the large toxins cross the endosomal membrane and ins A (TcdA) and B (TcdB), attack intracellular target proteins of host how the glucosyltransferase is reactivated in the cytosol remain cells by glucosylation. After receptor binding and endocytosis, the unknown. Moreover, the question of reactivation and refolding of toxins are translocated into the cytosol, where they modify target bacterial glycosyltransferases during and after translocation is proteins (e.g., Rho proteins). Here we report that the activity of enigmatic for many toxins/effectors known. In this study, we found translocated glucosylating toxins depends on the chaperonin that chaperonin TCP-1 ring complex (TRiC)/ chaperonin con- TRiC/CCT. The chaperonin subunits CCT4/5 directly interact with taining TCP-1 (CCT) plays a pivotal role in toxin translocation the toxins and enhance the refolding and restoration of the gluco- and/or refolding. TRiC/CCT is a molecular machine involved in syltransferase activities of toxins after heat treatment. Knockdown proper folding of a large number of newly synthesized eukaryotic of CCT5 by siRNA and HSF1A, an inhibitor of TRiC/CCT, blocks the proteins (24, 25). Approximately 10% of cytosolic proteins appear cytotoxic effects of TcdA and TcdB. In contrast, HSP90, which is to interact with TRiC/CCT (25, 26). The chaperonin is essential involved in the translocation and uptake of ADP ribosylating toxins, for the folding of many cytoskeleton proteins, including actin (27– is not involved in uptake of the glucosylating toxins. We show that 29) and tubulin (30, 31). We report that not only TcdA and TcdB, the actions of numerous glycosylating toxins from various toxin but also numerous other glycosylating toxins, including toxins/ types and different species depend on TRiC/CCT. Our data indicate effectors from Clostridia and Photorhabdus species, depend on the that the TRiC/CCT chaperonin system is specifically involved in toxin TRiC/CCT system. These findings provide insight into the actions uptake and essential for the action of various glucosylating protein and properties of glycosylating toxins that are translocated into toxins acting intracellularly on target proteins. the cytosol of host cells. chaperonin | toxin uptake | glycosyltransferase toxins | Results Clostridium difficile toxins | TRiC/CCT TRiC/CCT Interacts with TcdB and Other Glycosyltransferase Toxins. The initial aim of the study was to identify cytosolic interaction lycosylating protein toxins are major virulence factors of partners of glycosylating toxins in host cells. To this end, we used Gvarious pathogenic bacteria, including Clostridia, Legionella, C. difficile toxin TcdB and Legionella pneumophila effector SetA, Yersinia, Photorhabdus species, and Escherichia coli (1, 2). Pro- totypical members of this toxin/effector family are toxins A Significance (TcdA) and B (TcdB) from Clostridium difficile. This pathogen is the causative agent of antibiotic-associated diarrhea and pseu- domembranous colitis (3–5) and has emerged as a major Glucosylation of host proteins is a common pathogenicity mechanism of bacterial protein toxins. Prominent examples are healthcare threat in clinical settings (6). The clostridial gluco- Clostridium difficile sylating toxins TcdA and TcdB play pivotal roles in C. difficile toxins A and B, which inactivate Rho proteins infections (7). Related glucosylating toxins from Clostridium by glucosylation and cause diarrhea and pseudomembranous colitis in C. difficile infections. So far, host factors involved in sordellii and Clostridium novyi cause gas gangrene, necrotizing uptake and/or intracellular stabilization of the toxins are not fasciitis, and toxic shock syndrome (8, 9). known. Here we show that TRiC/CCT chaperonins interact with TcdA and TcdB have been in the focus of intensive research for glycosylating toxins and play an essential role in the intoxication two decades. The two toxins are related multidomain proteins process. Knockdown of chaperonins or inhibition of TRiC/CCT with an N-terminal glucosyltransferase domain (10), followed by functions by compound HSF1A prevents the cytotoxic effects of an autoprotease domain (11) and a large middle part of the toxins, glucosylating toxins. In contrast, HSP90, which is essential for which is crucial for toxin translocation into the cytosol (3, 12–15). ADP-ribosylating toxins, does not affect the uptake of glucosy- The C-terminal part of the toxins participates in binding to target lating toxins. Our data provide insight into the cellular actions of cells, involving possibly three cell membrane receptors: Frizzled glucosylating toxins. (16), poliovirus receptor-like 3 (PVRL3) (17), and chondroitin sulfate proteoglycan 4 (18). After endocytosis of the toxin- Author contributions: M.S., T.J., and K.A. designed research; M.S. performed research; receptor complex, the toxins translocate from an acidic endo- M.S., A.S., and T.J. analyzed data; M.S., A.S., T.J., and K.A. wrote the paper; and K.A. somal compartment into the cytosol, where the autoprotease do- supervised the study. main is activated by inositol hexakisphosphate (11, 19) to release The authors declare no conflict of interest. the glucosyltransferase domain. TcdA and TcdB glucosylate and This article is a PNAS Direct Submission. inhibit small GTP-binding proteins of the Rho family, including Published under the PNAS license. Rho, Rac, and Cdc42 proteins, which are master regulators of the 1To whom correspondence may be addressed. Email: [email protected] cytoskeleton and involved in numerous cellular processes (20, 21). freiburg.de or [email protected]. Up to date, the translocation of the glycosylating toxins into This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. the cytosol is the least understood process of the toxins’ actions. 1073/pnas.1807658115/-/DCSupplemental. Pore formation by TcdA and TcdB has been described (22, 23); Published online September 4, 2018. 9580–9585 | PNAS | September 18, 2018 | vol. 115 | no. 38 www.pnas.org/cgi/doi/10.1073/pnas.1807658115 Downloaded by guest on September 28, 2021 a glucosyltransferase that is translocated into eukaryotic cells by The function of TRiC/CCT depends on ATP binding and the Dot/Icm type-IV secretion system (32–34). Glucosyltransferase hydrolysis (31). We tested the nucleotide dependence of the SetA modified ∼60- and ∼40-kDa proteins in Jurkat cell lysate in restoration of TcdB activity by CCT4/5. While ATP largely en- the presence of UDP-[14C]glucose. Further studies focused on hanced the restoration after heat treatment in the presence of the 60-kDa protein that was identified by 2D gel electrophoresis CCT4/5, ADP had no effect (Fig. 1E). The addition of nucleo- and mass spectrometry as the T-complex protein 1e (CCT5) of tides did not affect the glucosyltransferase activity under control the chaperonin TRiC/CCT complex (SI Appendix, Fig. S1). Sub- conditions (SI Appendix, Fig. S3F). sequently, we observed that the glucosyltransferase domain of We next investigated whether other enzyme activities of bac- TcdB (TcdBGT) also directly interacted with CCT5 in precipi- terial toxins are protected and restored by CCT4/5. To this end, tation experiments, although it did not glucosylate CCT subunits we studied the binary ADP ribosylating toxin CDT from C. dif- (Fig. 1A). To analyze a direct interaction of TcdB with CCT in ficile and compared the effects of CCT4/5 with BSA on the more detail, we purified recombinant CCT4 and CCT5 and restoration of the enzyme activity after heat treatment. In con- performed binding studies using surface plasmon resonance trast to TcdB, the ADP ribosylating toxin CDT was not protected spectrometry. These studies revealed an affinity in the low mi- from heat inactivation by CCT4/5, indicating a specific effect of cromolar range between TcdBGT and CCT4 or CCT5 (SI Ap- the chaperonin on glycosylating toxins (SI Appendix, Fig. S4). pendix, Fig. S2 A–D). Moreover, a similar interaction with CCT5 was observed with the glucosyltransferase domains of C. sordellii Effects of the TRiC/CCT Inhibitor HSF1A. We next studied whether lethal toxin (TcsL) and C. novyi alpha toxin (TcnA) (Fig. 1A). CCT4/5 plays a role in the intoxication of intact cells by TcdB. We To study whether TRiC/CCT participates in the stabilization used HSF1A, which was recently identified as a specific inhibitor or refolding of glucosylating toxins, we used CCT4/5, because it of TRiC/CCT (36). TcdB (5 pM) induced almost complete has been reported that CCT4 and CCT5 can form biologically rounding up of HeLa cells after treatment for 90 min (Fig. 2 A and active homo-oligomers (35). We pretreated TcdB at different B). HSF1A blocked the intoxication process in a concentration- temperatures (37°, 42°, 48°, and 55 °C) for 15 min in the presence dependent manner. While initial effects were observed at 10 μM, of ATP. Then the reaction mixture was cooled to 30 °C in the HSF1Aat50μM completely blocked TcdB-induced cytotoxicity. presence of CCT4/5, followed by toxin-catalyzed glucosylation of We also tested the in vivo glucosylation of Rac1 protein, which is GST-tagged RhoA or Rac1 (Fig. 1 B–D and SI Appendix, Fig. S3 targeted by TcdB (Fig. 2C). Therefore, we used an anti-Rac1 B and C). We used a 1:1 mixture of CCT4 and CCT5, because antibody that recognizes only nonmodified Rac1 (37).