Cholera toxin binds to which receptors in intestine-

Ans. is 'd' i.e., GM1 gangliosides through B subunito V. cholerae produces cholera toxin, the model for enterotoxins, whose action on the mucosal epithelium is responsible for the characteristic diarrhoea of the cholera. Cholera toxin resembles heat labile toxin of E. coli.o Cholera toxin is a protein complex made up of six subunits --> a single copy of'A' subunit (Port A) and five copies of 'ET subunit (Part B). 'A' subunit has two fragments; Ai and A2. Cholera toxin |||A subunit (active part)B subunit|||| |Al fragmentA2 fragmentBinds to GM1 Ganglioside|| A DP ribosylation of G-proteinLinks the A, fragment to B subunit|Stimulation of adenyl cyclase and increased production of cAMPo cAMP inhibits the absorptive sodium transport system (decreases sodium & chloride reabsorption) and activates the secretory chloride transport system (increases chloride and bicarbonate secretion)o This leads to accumulation of sodium choride in the intestinal lumen.o Accumulated sodium chloride draws water into the lumen due to increased osmolality leading to watery diarrhoea.o Cholera toxin production is determined by a filamentous phage integrated with bacterial chromosome.o Endotoxin has no role in pathogenesis.