Cholera toxin between

Dallas WS, Falkow S Amino acid sequence homology between cholera toxin and Escherichia coli heat-labile toxin. Nature 1980 288 499-501. 

C. botulinum toxins belong to the AB group of toxins, which also includes diphtheria toxin, pseudomonas exotoxin A, anthrax toxin, Shiga(like) toxin, cholera toxin, pertussis toxin, and plant toxins, e.g., ricin. Moiety A has an enzymatic activity and usually modified cellular-target entering cytosol. Moiety B consists of one or more components and binds the toxin to surface receptors, and is responsible for translocation of the A component into cells. AB toxins are produced in a non-active form and are activated by a split between two cysteine residues within a region (Falnes and Sandvig, 2000). 

Ellipsometry can follow the interactions between two types of biological macromolecules, the first of those two bound physically to the surface, the other acting from the solution. The binding of conconavalin A to adsorbed mannan 180) and of cholera toxin to adsorbed ganglioside t83) are examples. The adsorption of complement factors to an antibody-coated surface was monitored by ellipsometry and a modification of the same method was used for quantification of migration inhibition of human polymorphonuclear leucocytes 182). Interaction of proteins and cells with affinity ligands covalently coupled to silicon surfaces has been also studied 183). 

Fig. 18.3. Schematic representation of the photoaffinity immobilization of the antibody cholera toxin (anti-CT). After irradiation of the photobiotin layered electrode in presence of the antibody, a covalent bond has been formed between the electrode and the antibody keeping its accessibility for immunoreactions with HRP-IgG anti-rabbit antibody.

The dopamine-stimulated formation of cAMP may initiate the dopamine-induced release of IR-PTH. A linear relationship exists between the dopamine-induced release of IR-PTH and the logarithm of the dopamine-induced accumulation of cAMP (17). Similarly, other agents increasing cAMP accumulation and IR-PTH release (e.g. beta-adrenergic agonists, secretin and phosphodiesterase inhibitors, also display such a log-linear relationship. Additional support for the possibility that intracellular cAMP might initiate PTH secretion comes from the observations that cholera toxin (JJ.), phosphodiesterase inhibitors (17) and dibutyryl cAMP (18), agents known to increase intracellular cAMP or mimic the biochemical effects of cAMP, increase the release of IR-PTH. 

Gershengorn et al. [9] found in thyrotropic tumor cells in culture that cAMP analogues, phosphodiesterase inhibitors and cholera toxin caused an increase in TSH release that was additive to that of TRH, that there was no correlation between TSH release and cAMP levels and that there was no change in binding of cAMP to protein kinase, suggesting that cAMP is not the physiological mediator of TRH-in-duced TSH release. 

Evidence from in vivo experiments after administration of hCG suggested that a lesion develops between the LH receptor and the adenylate cyclase in rat testis cells and ovarian cells (see Ref. 69 for other references). Further work carried out in vitro with tumour Leydig cells demonstrated that LH produced a decrease in LH stimulation of adenylate cyclase in intact cells. This loss of response persisted in plasma membranes prepared from the desensitized cells [70]. The response of the intact cells to cholera toxin and of the plasma membranes to fluoride and p(NH)ppG were not decreased. These studies suggested that the lesion occurred between the LH receptor and Gs, whereas the coupling between Gs and the adenylate cyclase catalytic unit was intact. Such a conclusion is in agreement with that of other workers investigating the catecholamine-induced desensitization of S49 lymphoma cells [71,72], This lesion may be necessary before internalization of the receptor can occur. 

There is another large class of receptors whose occupancy by an agonisf leads to inhibition of adenylate cyclase. These include the tt2 adrenergic receptors, receptors for acetylcholine, adenosine, prostaglandin E2 (Chapter 21), somatostatin, and some receptors for dopamine. Their responses are mediafed by inhibitory proteins Gj, which closely resemble Gg in their sizes, amino acid sequences, and heterotrimeric structures, but which inhibit adenylate cyclase when activated. A clear distinction between the Gg and Gj proteins is evident in the fact that Gg is irreversibly activated by the action of cholera toxin, while G loses its ability to respond to occupied receptors when modified by the action of Pertussis toxin (Box 11-A). A specialized heterotrimeric G protein known as transducin mediates the light-induced activation of a cyclic GMP phosphodiesterase in the retina " (see Chapter 23). Its a subunit is designated aj. The related gustducin is found in taste buds. ... 

Munoz, E., Zubi, A.M., Merrow, M., Sauter, N.P. and Huber, B.T. (1990b). Cholera toxin discriminates between T helper 1 and 2 cells in T cell receptor-mediated activation role of cAMP in T cell proliferation. J. Exp. Med. 172, 95-103. 

Picking WL, Moon H, Wu H, et al. (1995) Fluorescence analysis of the interaction between ganglioside GMi-containing phospholipid vesicles and the B subunit of cholera toxin. In Biochim. Biophys. Acta 1247 65—73. 

Tsai S-C, Adamik R, Moss J, etal. (1991) Guanine nucleotide-dependent formation of a complex between choleragen (cholera toxin) A subunit and bovine brain ADP-ribosylation factor. In Biochemistry 30 3697-3703. 

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