Diphtheria Structure

Page 1170 (Figure 28 5) is adapted from crystallographic coordinates deposited with the Protein Data Bank PDB ID IDDN White A Ding X Vanderspek J C Murphy J R Ringe D Structure of the Metal Ion Activated Diphtheria Toxin Re pressor/Tox Operator Complex Nature 394 p 502 (1998)... 

FIGURE 10.32 The structures of (a) S-eudotoxiu (two views) from Bacillus thuringiensis and (b) diphtheria toxin from Cmynehacterium diphtheriae. Each of these toxins possesses a bundle of a-hehces which is presumed to form the trausmembraue channel when the toxin Is Inserted across the host membrane. In S-endotoxln, helix 5 (white) Is surrounded by 6 helices (red) In a 7-hellx bundle. In diphtheria toxin, three hydrophobic helices (white) lie at the center of the transmembrane domain (red). 

Colliei R.J., and Kandel, J. (1971) Structure and activity of diphtheria toxin./. Biol. Chem. 246, 1496-1503. 

The structural differences between bacterial and eukaryotic elongation factors are highlighted by the selective action that diphtheria has on eukaryotic systems (box 29B). 

Collier, R. J., and Cole, H. A. (1969) Diphtheria toxin subunit active in vitro. Science 164,1179. Collier, R. J., and Kandel, J. (1971) Structure and activity of diphtheria toxin. J. Biol. Chem. 246, 1496-1503. 

Uherek, C., Fominaya, J. and Weis, W. (1998) A modular DNA carrier protein based on the structure of Diphtheria Toxin mediates target cell-specific gene delivery. J. Biol. Chem., 273, 8835-8841. 

A few years ago, we began a research program to develop methods of analysis which would involve the use of FAB and a high performance tandem mass spectrometer. The tandem instrument was the first triple sector mass spectrometer to be designed and built by a commercial instrument company (Kratos of Manchester, U.K.). The first mass spectrometer of the combination is a double focussing Kratos MS-50 which is coupled to a low resolution electrostatic analyzer, which serves as the second mass spectrometer U). This FAB MS-MS combination has been used to verify the structures of an unknown cyclic peptide (2), a new amino acid modified by diphtheria toxin (3), and an ornithine-containing lipid (4). A number of methods have also been worked out which rely on this instrumentation. They Include the structural determination of cyclic peptides (5), nucleosides and nucleotides (6), and unsaturated fatty acids (7) and the analysis of mixtures of both anionic (8) and cationic surfactants (9). 

Starch-like substances are produced in several species of bacteria.18,21 For example, Escherichia coli produces a linear glucan.21,29 Corynebacterium diphtheriae produces a starch-like material and Clostridium butyricum produces a glucan with some branching.21 Neisseria perflava produces a glucan, intermediate in structure between amylopectin and glycogen 29 however, more recent work shows that the structure more closely approaches that of glycogen.30... 

Pohl E, Holmes RK, Hoi WGJ. Motion of the DNA-binding domain with respect to the core of the diphtheria toxin repressor (DtxR) revealed in the crystal structures of apo- and holo-DtxR. J. Biol. Chem. 1998 273 22420-22427. 

White A, Ding X, vander Spek JC, Murphy JR, Ringe D. Structure of the metal-ion-activated diphtheria toxin repressor/tox operator complex. Nature 1998 394 502-506. 

B.T. Porse and RA. Garrett. 1999. Ribosomal mechanics, antibiotics, and GTP hydrolysis Cell 97 423-426. (PubMed) D. Eisenberg. 1992. The crystal structure of diphtheria toxin Nature 357 216-222. (PubMed)... 

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]. 

Wilson BA, Collier RJ (1992) Diphtheria toxin and Pseudomonas aeruginosa exotoxin A Active-site structure and enzymatic mechanism. In Curr. Top. Microbiol. Immunol. 175 27-41. 

Unlike diphtheria toxin, little is known about the structures required for the translocation of the enzymatic subunit of PT. In diphtheria toxin and Pseudomonas aeruginosa exotoxin A, the B moiety can be clearly subdivided into two distinct domains, one responsible for receptor binding, composed essentially of (3 sheets, and one responsible for translocation of the A subunits, essentially composed of a helices (Allured etal., 1986 Choe etal., 1992). There is no clear translocation domain in PT, and much less is known about the internalization step of PT, compared to diphtheria toxin and exotoxin A. 

Structural homologies between PFTs and other toxins have not been identified. However, the process of membrane permeabilization may be operative in many cases where proteins have to escape from an intracellular compartment. Well known examples are diphtheria toxin, the neurotoxins and anthrax toxin. Specific domains in many intracel-lularly active toxins have in fact been shown to produce pores in artificial lipid bilayers, and membrane permeabilization is thought to form the basis for translocation of the active moieties from the late endo-some to the cytoplasm (reviewed in Montecucco et ai, 1994). The molecular mechanism of this translocation remains obscure. In the... 

Fig. 1. Schematic structure of intact and nicked diphtheria toxin (a) and of a fusion protein where a passenger protein has been fused to the N-terminus of the A-fragment (b)...

Diphtheria toxin is produced as a single polypeptide chain (Fig. la) yyhich is easily cleaved ("nicked") by trypsin and trypsin-like proteases into two disulfide-linked fragments, A and B (Pappenheimer, 1977). The structure of the nicked toxin resembles that of the plant toxins ricin, abrin, modeccin, viscumin and others (Olsnes and Sandvig, 1985). 

Van Ness BG, Howard JB, Bodley JW (1980) ADP-ribosylation of elongation factor 2 by diphtheria toxin. NMR spectra and proposed structure of ribosyl-diphthamide and its hydrolysis products. J Biol Cbem 255 10710-10716. 

Most exotoxins fall into one of three categories on the basis of their structure and activities. These are the A-B toxins, the cytolytic toxins and the superantigen toxins. The A-B toxins consist of a B subunit that binds to a host cell receptor, covalently bound to the A subunit that mediates the enzymic activity responsible for toxicity. Most exotoxins (e.g. diphtheria toxin, cholera toxin) are of the A-B category. The cytolytic toxins such as haemolysins and phospholipases do not have separable A and B... 

---