Cholera toxin (secreted by the bacterial pathogen, Vibrio cholera) disrupts the

Question

Cholera toxin (secreted by the bacterial pathogen, Vibrio cholera) disrupts the normal regulation of G protein signaling. Which of the following cell conditions listed below likely would be the most effective in counteracting the adverse effect of adding cholera toxin to the cells? A. Inhibition of GPCR GEF activity B. Overexpress ion of a constitutively active mutant form of the G-alpha-i subunit C. Mutation of the GPCR ligand binding domain D. Deletion of the G-beta subunit E. Simultaneous addition of Bordetella pertussis toxin

Explanation / Answer

Cholera is an incredibly dangerous disease, caused by Vibrio cholerae; the microbe releases a toxin into the intestinal tract that causes massive diarrhea through electrolyte loss. It is transmitted through contact with human feces-contaminated food and water, poor sanitation. The main reason that our body may not want to induce a potent immune attack against Vibrio cholerae is that Vibrio cholerae produce toxins as antigens.

Cholera toxin is made up of five identical B subunits and one “A subunit.” In causing cholera, first one of the B subunits of cholera toxin binds to a glycolipid receptor in the cytoplasmic membrane of an intestinal epithelial cell. Then, when the A subunit is cleaved, a portion of it known as A1 enters the cell’s cytosol, acting as an enzyme and activating adenylate cyclase.

After adenylate cyclase is activated, it enzymatically converts ATP (adenosine triphosphate) into cyclic AMP (cAMP), which stimulates secretion of excess levels of electrolytes from the cell. Through osmosis, water follows the electrolytes out of the cell into the intestinal lumen. This process results in the severe diarrhoea characterizing cholera.

Thus, the correct options are:

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