Produced by Vibrio cholerae, cholera toxin (CT) can bind to many types of cells; after binding to neurons, CT travels along the neuron toward the central nervous system, marking the way. In addition to this interesting property, cholera toxin is an enzyme which catalyzes the ADP-ribosylation of the Gs protein. Because Gs proteins are involved in many different chains of events which control cellular activity, cholera toxin enzyme is used to manipulate and study a variety of cellular responses.
Cholera toxin is a two-part toxin consisting of the enzymatic A subunit and a B subunit, actually a pentamer composed of five identical small proteins. Cholera toxin B subunit (CT B) binds with high efficiency to GM1 monosialoganglioside cell membrane receptors, present in many cell types, allowing use of CT experimentally in cell culture. Cholera toxin B subunit retains the full binding capacity of the intact toxin yet has the advantage of being completely nontoxic. When injected in a nerve, the toxin binds to the neuron membrane and moves retrogradely along the neuron. Antibodies directed to B subunit allow the visualization of neurons and their connections, track tracing. B subunit is conjugated to flourophores and small tags such as biotin, allowing different methods for visualizing neuronal paths.
When CT intoxicates a cell, it first binds to receptors, under goes endocytosis and travels to the endoplasmic reticulum where the enzymatically active A subunit (CTA) is translocated to the cytosol. Within the cytosol, the A subunit catalyzes ADP-ribosylation of the Gs protein, which activates adenylate cyclase and as a consequence increases the intracellular concentration of cAMP. Due to its natural ability to interact with this Gs molecular switch, cholera toxin is used to study signal transduction.
Interestingly, cholera toxin effectively modulates mammalian immune systems and acts as an adjuvant for co-administered antigens.
List Labs offers both the whole toxin CT and the B subunit as research reagents.
Cholera toxin reagent is produced and activated in native fermentation cultures of Vibrio cholerae. It is purified and tested for binding with ganglioside receptor GM1 coated plates; results are available in lot specific C of A’s. This is a highly purified reagent; both purity and low endotoxin content are measured and reported. It is described as azide-free because earlier products from List Labs were provided in a buffer containing the bacteriostatic agent, sodium azide. Purity of current product is maintained by filtration and aseptic processing.
List Labs purifies cholera toxin B subunit from native fermentation cultures of Vibrio cholerae. Toxin is first purified, disassembled and pure B subunit recovered. It is provided in a low-salt buffer required for use in track tracing along with our antibody (Product #703) but also suitable for many other uses. This protein is also called “choleragenoid”.
High titer polyclonal anti-cholera B subunit from goat, suitable for use in either toxin neutralization or binding assays, is available as a lyophilized powder. This antibody is also used along with B subunit for microscopic identification of neural connections. Antibody is tested for reactivity to CT B.
Conjugates of cholera toxin B subunit have been employed as histochemical markers in both axoplasmic transport and neuronal connectivity studies. The basis of this lies in the binding specificity of choleragenoid to GM1 ganglioside receptors on neuronal cell surfaces. List Labs offers cholera toxin B subunit conjugated to fluorescein (FITC), a sensitive fluorescent probe suitable for use in flow cytometry and microscopy, and biotinylated cholera toxin B subunit for high affinity cytochemistry for microscopy. Each of these conjugates are supplied as aseptically packaged lyophilized powders. Detailed lot analysis and instructions on reconstitution, storage and handling are provided with each shipment.