Diphtheria toxin factor

A different kind of enzyme, translocase [80700-39-6], which transfers a fragment of NAD to the protein—synthesis factor (elongation factor 2), is catalyzed by diphtheria toxin, thereby inhibiting protein synthesis (43). In tumor cells, the rate of protein synthesis is 100 to 1000 times more sensitive to diphtheria toxin than the analogous process in normal cells (41) therefore, diphtheria toxin is selectively toxic to tumor cells. 

Diphtheria toxin, Pseudomonas exotoxin A Elongation factor 2 ADP-ribosylation Inhibition of protein synthesis (diphtheria, Pseudomonas infection)... 

Shimisu, N., Nickimins, W.K., and Shimizu, Y. (1980) A cytotoxic epidermal growth factor cross-linked to diphtheria toxin A-fragment. FEES Lett. 118, 274. 

A third type of bacterial toxin, diphtheria toxin, catalyzes the ADP-ribosylation of eukaryotic elongation factor (EFTU), a type of small G protein involved in protein synthesis (Table 19-2). The functional activity of the elongation factor is inhibitedby this reaction. Finally, a botulinum toxin ADP-ribosylates and disrupts the function of the small G protein Rho, which appears to be involved in assembly and rearrangement of the actin cytoskeleton (Table 19-2). These toxins maybe involved in neuropathy (see Ch. 36) and membrane trafficking (see Ch. 9). 

In eukaryotic cells, elongation factor-2 (eEF-2) used in translocation is inactivated through ADP-ribosylation by Pseudomonas and Diphtheria toxins. 

Diphtheria toxin Bacterium A-B ADP ribosylation of elongation factor-2 ... 

A close relative of immunotoxins is the growth factor fusion toxin, in which antibody is replaced with a ligand or growth factor to provide selectively of the toxin domain in immunotoxin. One such molecule, containing human interleukin-2 (IL-2) fused to truncated diphtheria toxin (denileukin diftitox or Ontak), was approved by the FDA in 1999. 

Several other inhibitors of protein synthesis are notable because of their toxicity to humans and other mammals. Diphtheria toxin (Mr 58,330) catalyzes the ADP-ribosylation of a diphthamide (a modified histidine) residue of eukaryotic elongation factor eEF2, thereby inactivating it. Ricin (Afr 29,895), an extremely toxic protein of the castor bean, inactivates the 60S subunit of eukaryotic ribosomes by depurinating a specific adenosine in 23S rRNA. 

Factor EF-G from eukaryotes (eEF2) is similar to the bacterial protein, but its interaction with the larger eukaryotic ribosomes seems to be more complex. For example, interaction with the ribosomal stalk is more extensive.37 EF2 contains a single modified histidine called diphthamide.397 This amino acid is not found in other proteins but is always present in eukaryotic EF2 and also in EF-G from archaeobacteria. It is the site of modification by diphtheria toxin (Box 29-A). 

Inactivation of the EF-2 factor by diphtheria toxin through the ADP-ribosylation of a modified histidine side chain. 

Ramon G, Descombey P (1925) Sur 1 immunization antitetanique et sur la production de l antitoxine tetanique Compt Rend Soc Biol 93 508-98 Ratts R, Zeng H, Berg EA, Blue C, McComb ME et al. (2003) The cytosolic entry of diphtheria toxin catalytic domain requires a host cell cytosolic translocation factor complex. J Cell Biol 160 1139-50... 

E. S. Massuda, E. J. Dunphy, R. A. Redman, J. J. Schreiber, L. E. Nauta, F. G. Barr, I. H. Maxwell, and T. P. Cripe, Regulated expression of the diphtheria toxin A chain by a tumor-specific chimeric transcription factor results in selective toxicity for alveolar rhabdomyosarcoma cells, Proc. Natl. Acad. Sci. USA 94 14701 (1997). 

Figure 12.4 Inhibition of protein synthesis by diphtheria toxin transfer of an ADP-ribose moiety from NAD+ to a diphthamide residue in the elongation factor EF-2.

The ribosomal elongation Factor 11 is the acceptor protein for the ADP-ribosyltransferase activity of diphtheria toxin and P. aeruginosa exotoxin A, as well as a mammalian cytosolic ADP-ribosyltransferase. ADP-ribosylation results in loss of activity. The uncontrolled action of the bacterial toxins causes the cessation ofprotein synthesis andhence cell death. The more regulated action of the endogenous ADP-ribosyltransferase is part of the normal regulation of protein synthesis. 

Arora, N., Leppla, S.H. (1993). Fusions of anthrax toxin lethal factor with shiga toxin and diphtheria toxin enzymatic domains are toxic to mammalian cells. Infect. Immun. 62 4955-61. 

Figure 29.35. Blocking of Translocation by Diphtheria Toxin. Diphtheria toxin blocks protein synthesis in eukaryotes by catalyzing the transfer of an ADP-ribose unit from NAD+ to diphthamide, a modified amino acid residue in elongation factor 2 (translocase). Diphthamide is formed by a posttranslational modification (blue) of a histidine residue.

Family resemblance. Eukaryotic elongation factor 2 is inhibited by ADP ribosylation catalyzed by diphtheria toxin. What other G proteins are sensitive to this mode of inhibition ... 

Certain inhibitors - kirromycin, pulvomycin, fusidic acid and diphtheria toxin - which block protein synthesis by interacting with either elongation factor constitute potent probes to reveal eucaryal and/or bacterial traits on archaeal factors. 

The structurally related antibiotics kirromycin and pulvomycin both act upon EF-Tu of most bacteria (and chloroplasts) although not upon its eucaryal (EF-la) counterpart [158,159]. The steroid antibiotic fusidic acid interacts systematically with both the eucaryal (EF-2) and the bacterial (EF-G) translocating factors, including chloroplasts of higher plants. Diphtheria toxin (fragment A) discriminates between bacterial-mitochondrial and eucaryal translocating factors by selectively and irreversibly impairing the eucaryal EF-2 factors [160,161]. 

The results of in vitro assays, summarized in Table 9, show that archaea exhibit a uniform response to two of the factor-targeted inhibitors (diphtheria toxin and kirromycin) while being heterogeneous in their response to the other two (fusidic acid and pulvomycin). 

Archaea are systematically susceptible to ADP-ribosylation from NAD by the diphtheria toxin [118,166-168] although the rate of the ADP-ribosylation reaction is three orders of magnitude slower than that typically observed with eucaryal EF-2 [164,168]. Furthermore, in accordance with the sensitivity data, diphthamide occurs in archaea (//. halobium) but not in bacteria ( . coli) [164]. The archaeal EF-G-equivalent factor, therefore, resembles the eucaryal factor in having both the diphthamide that acts as the receptor for the ADP-ribose moiety of NAD, and the enzyme system which assists the post-translational conversion of histidine to diphthamide. 

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