Molecular Mechanism of Cholerae Toxin (ctx) in Causing Diarrhea
DOI:
https://doi.org/10.30649/obj.v1i2.16Keywords:
Vibrio cholerae, cholerae toxin (ctx), type II secretion (T2S), GM1 ganglioside, adenilate cyclase, T0xR geneAbstract
Vibrio cholerae is one of the pathogenic bacteria transmitted through contaminated
food, especially contaminated seafood and beverages. V. cholerae produces cholerae toxin
(ctx) which is encoded by the ctx gene located within its chromosome. This toxin has been
recognized as one of the toxins responsible for cholera outbreaks. The mechanism of ctx gene
expression is induced by environmental signals such as pH, osmolarity, temperature, bile,
amino acids, and CO2. These signals will be a positive transcriptional factor to the ToxR gene
that regulates the biogenesis of cholerae toxin. After cholerae toxin has been successfully
expressed, V. cholerae uses a type II secretion (T2S) pathway to deliver cholerae toxin to the
extracellular environment. Cholerae toxin consists of A and B subunits. The B subunit plays
a role in attaching to the receptor Manosialosyl Ganglioside (GM1 ganglioside) and the A
subunit plays a role in catalyzing ADP-ribosylation of Gs (stimulatory) protein and turning
them into active condition. The Gs protein will convert the inactive adenilate cyclase (AC)
into active AC. The increase of AC activity will increase the cyclic adenosine 3'5'-
monophosphate (cAMP) concentration along the cell membrane. The cAMP then causes the
active secretion of sodium (Na+), chloride (Cl-), potassium (K+), bicarbonate (HCO3-), and water (H2O) out of the cell into the intestinal lumen, resulting in large fluid losses and
electrolyte imbalances.
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