title: Generation of a potent chimeric toxin by replacement of domain III of Pseudomonas exotoxin with ricin A chain KDEL.
abstract: Following cellular uptake, Pseudomonas exotoxin (PE) is cleaved by cellular protease which generates an enzymatically active C-terminal fragment (amino acids 280-613). This 37 kD fragment translocates to the cell cytosol where it ADP-ribosylates elongation factor 2 and inhibits protein synthesis. A recombinant hybrid toxin (designated PE-RTA) in which the ADP-ribosylation domain (domain 111) was replaced by the RNA N-glycosidase domain of ricin (the A chain or RTA) has been produced in E. coli. The hybrid toxin effectively and specifically depurinated 28S ribosomal RNA, indicating that the ricin A moiety folded into its native conformation. The cytotoxicity of PE-RTA for L929 cells was approximately 100-fold less than either native PE or whole ricin. However, the addition of the tetrapeptide KDEL to the C-terminus of PE-RTA (producing PE-RTA KDEL) increased cytotoxicity to the level of the native toxins. By analogy to PE, both PE-RTA and PE-RTA KDEL would be proteolytically cleaved within PE domain II during cell entry. A single amino acid substitution, believed to disrupt an essential step in the transport of the catalytically active PE fragment to the cell cytosol (Trp281 to Ala: Zdanovsky, A.G., Chiron, M., Pastan, I., and FitzGerald, D. J. (1993) J. Biol. Chem. 268, 21791-21799), reduced the cytotoxicities of both PE and PE-RTA KDEL by approximately 100-fold. Taken together, these data show that the ricin A chain component of the hybrid toxin requires essential PE-derived sequences at both the N- and C-termini of the translocating fragment. Clearly, in the context of this fusion protein, ricin A chain cannot effect its own transfer to the cytosol.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry, U.K.
authors.forename: C
authors.initials: C
authors.lastname: Pitcher
authors.forename: L
authors.initials: L
authors.lastname: Roberts
authors.forename: S
authors.initials: S
authors.lastname: Fawell
authors.forename: A G
authors.initials: AG
authors.lastname: Zdanovsky
authors.forename: D J
authors.initials: DJ
authors.lastname: FitzGerald
authors.forename: J M
authors.initials: JM
authors.lastname: Lord
mesh_terms: D036002:ADP Ribose Transferases; D000595:Amino Acid Sequence; D000818:Animals; D001427:Bacterial Toxins; D002460:Cell Line; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005098:Exotoxins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity; D051379:Mice; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry* / Q000235:genetics; D021382:Protein Sorting Signals; D011500:Protein Synthesis Inhibitors / Q000737:chemistry / Q000633:toxicity; D011550:Pseudomonas aeruginosa; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity; D012276:Ricin / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D005098:Exotoxins; D009842:Oligopeptides; D021382:Protein Sorting Signals; D011500:Protein Synthesis Inhibitors; D011993:Recombinant Fusion Proteins; D012276:Ricin; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C073762:lysyl-aspartyl-glutamyl-leucine