Toxin Action: Molecular Mechanisms


Toxins are compounds of different nature, including cytotoxic proteins, polypeptides of variable lengths, alkaloids and others. They are produced by different organisms and are poisonous to animals. Toxins act by affecting functions that are essential to the survival of the cell or to its communication with its environment. Because the action of many toxins is highly specific for a particular cellular target, toxins have been valuable in elucidating the mechanisms that maintain and control essential cellular functions.

Keywords: G protein; signal transduction; neurotoxin; ion channel

Figure 1.

Effects of cholera toxin (CT) and pertussis toxin (PT) on the GTPase cycle of G proteins. HR, hormone receptor; Pi, inorganic phosphate. See text for details.

Figure 2.

Schematic presentation of the transmembrane arrangement of the principal subunits of voltage‐gated ion channels. Sodium and calcium channels share the general structure of four homologous repeated domains (I–IV) that are organized in the membrane around a central pore, the ion‐conducting pathway. The potassium channel is composed of four polypeptides, each homologous to one repeat of the sodium or calcium channel domains. Each domain consists of six putative transmembrane α‐helical segments (S1–S6). The most highly conserved segment is S4, which contains a unique motif of a positively charged amino acid residue followed by two nonpolar residues that is repeated four to eight times in each S4 helix. These S4 structures, which participate in the voltage‐sensing mechanism, are indicated in each domain by a (+) sign. The short segments (SS1 and SS2), which are invaginations of the loops between transmembrane segments S5 and S6, form part of the ion‐conducting pathway, the ‘pore region’ (area bounded by a jagged line). Black triangles represent the external vestibules of the pore. The linker connecting domains III and IV in the sodium channels represents a region that is thought to participate in the fast inactivation process.



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Further Reading

Hille B (1992) Ionic Channels of Excitable Membranes. Sunderland, MA: Sinauer.

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Cassel, Dan, Menez, Andre, and Gordon, Dalia(Jan 2003) Toxin Action: Molecular Mechanisms. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001406]