Q.42 Cholera toxin increases cAMP levels by
(A) modifying Gi protein
(B) modifying Gs protein
(C) binding to adenylate cyclase
(D) activating cAMP phosphodiesterase

Cholera Toxin Increases cAMP Levels by Modifying Gs Protein

Cholera toxin elevates cAMP levels through a specific biochemical mechanism central to Vibrio cholerae’s pathogenesis. The correct answer to this multiple-choice question is option (B). This SEO-optimized article breaks down the mechanism and all options for biotechnology and microbiology students.

Correct Answer

Cholera toxin increases cAMP levels by modifying Gs protein. It ADP-ribosylates the alpha subunit of Gs, locking it in an active state that continuously stimulates adenylate cyclase to produce cAMP. This leads to excessive cAMP accumulation, disrupting ion transport and causing diarrhea.​

Option Analysis

(A) Modifying Gi Protein

Gi protein inhibits adenylate cyclase, reducing cAMP levels. Modifying Gi would decrease cAMP, opposite to cholera toxin’s effect. Pertussis toxin, not cholera toxin, targets Gi.​

(B) Modifying Gs Protein

Correct. Cholera toxin’s A subunit catalyzes ADP-ribosylation of Gsα, preventing GTP hydrolysis and prolonging adenylate cyclase activation. This sustains high cAMP production.​

(C) Binding to Adenylate Cyclase

Cholera toxin does not bind adenylate cyclase directly. It acts via Gs protein modification to indirectly activate the enzyme. Direct binding is not the mechanism.​

(D) Activating cAMP Phosphodiesterase

cAMP phosphodiesterase degrades cAMP, lowering its levels. Cholera toxin does not activate this enzyme; it promotes cAMP buildup by enhancing synthesis.​