Which of the following bacteria act by increasing cAMP.
Correct Answer: Vibrio cholera
Description: Ans. is 'a' i.e. Vibrio cholera Cholera produces a potent enterotoxin known as cholera toxin.This toxin consists of five B subunits and a single A subunit and has structural, functional and antigenic similarity to heat-labile toxin expressed by strains of enterotoxigenic Escherichia coltThe A subunit of the toxin is made up of two peptides (A1 and A2), linked by a single disulphide bridge.The B subunit binds to sugar residues of ganglioside GM1on the cells lining the villi and crypt of the small intestine (V. cholera never invades the intestinal epithelium but remain within the lumen and secretes the cholera toxin).It is believed that the insertion of the B subunit into the host cell membrane forms a transmembrane channel through which a toxic A subunit can pass into the cytoplasm.The cholera enterotoxin causes the transfer of adenosine diphosphoribose (ADP ribose) from nicotinamide ademine dinucleotide (NAD} to a regulatory protein, which is part of the adenylate cyclase enzyme responsible for the generation of intracellular cyclic adenosine monophosphate (cAMP).The result is irreversible activation of adenylate cyclase and overproduction of cAMP.This in turn causes inhibition of uptake of Na+ and Cl- ions by cells lining the villi, together with hypersecretion of Cl- and HCO3-ions.This blocks the uptake of water which normally accompanies Na+ and Cl- absorption and there is passive net outflow of water across mucosal cells leading to serious loss of water and electrolytes.Heat stable toxin of E.coli acts through cGMP.
Category:
Microbiology
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