title: FK506-binding protein 51 interacts with Clostridium botulinum C2 toxin and FK506 inhibits membrane translocation of the toxin in mammalian cells.
abstract: The binary Clostridium botulinum C2 toxin consists of the binding/translocation component C2IIa and the separate enzyme component C2I. C2IIa delivers C2I into the cytosol of eukaryotic target cells where C2I ADP-ribosylates actin. After receptor-mediated endocytosis of the C2IIa/C2I complex, C2IIa forms pores in membranes of acidified early endosomes and unfolded C2I translocates through the pores into the cytosol. Membrane translocation of C2I is facilitated by the activities of host cell chaperone Hsp90 and the peptidyl-prolyl cis/trans isomerase (PPIase) cyclophilin A. Here, we demonstrated that Hsp90 co-precipitates with C2I from lysates of C2 toxin-treated cells and identified the FK506-binding protein (FKBP) 51 as a novel interaction partner of C2I in vitro and in intact mammalian cells. Prompted by this finding, we used the specific pharmacological inhibitor FK506 to investigate whether the PPIase activity of FKBPs plays a role during membrane translocation of C2 toxin. Treatment of cells with FK506 protected cultured cells from intoxication with C2 toxin. Moreover, FK506 inhibited the pH-dependent translocation of C2I across membranes into the cytosol but did not interfere with the enzyme activity of C2I or binding of C2 toxin to cells. Furthermore, FK506 treatment delayed intoxication with the related binary actin ADP-ribosylating toxins from Clostridium perfringens (iota toxin) and Clostridium difficile (CDT) but not with the Rho-glucosylating Clostridium difficile toxin A (TcdA). In conclusion, our results support the hypothesis that clostridial binary actin-ADP-ribosylating toxins share a specific FKBP-dependent translocation mechanism during their uptake into mammalian cells.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Ulm Medical Center, Albert-Einstein-Allee 11, Ulm, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Kaiser
authors.forename: Natalie
authors.initials: N
authors.lastname: Böhm
authors.forename: Katharina
authors.initials: K
authors.lastname: Ernst
authors.forename: Simon
authors.initials: S
authors.lastname: Langer
authors.forename: Carsten
authors.initials: C
authors.lastname: Schwan
authors.forename: Klaus
authors.initials: K
authors.lastname: Aktories
authors.forename: Michel
authors.initials: M
authors.lastname: Popoff
authors.forename: Gunter
authors.initials: G
authors.lastname: Fischer
authors.forename: Holger
authors.initials: H
authors.lastname: Barth
mesh_terms: D000818:Animals; D001905:Botulinum Toxins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D006367:HeLa Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D011485:Protein Binding; D016559:Tacrolimus / Q000494:pharmacology; D022021:Tacrolimus Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D014709:Vero Cells; D000099159:Tacrolimus Binding Protein 5
chemical_list: D001905:Botulinum Toxins; D018841:HSP90 Heat-Shock Proteins; D016559:Tacrolimus; D022021:Tacrolimus Binding Proteins; D000099159:Tacrolimus Binding Protein 5; C096324:botulinum toxin type C