Interaction of Cholera Toxin with its Receptor the Monosialoganglioside GM1: A Fluorescence Study
Cholera toxin (CT) is an enterotoxin secreted by Vibrio cholerae producing its pathological effects by increasing the c-AMP level in intestinal epithelial cells1,2. It is an oligomeric protein (Mr ~ 84,000) composed of two structural and functional distinct subunits CT A and CT B (Mr ~ 29,000 and 55,000 respectively). CT B contains five identical polypeptide chains (Mr = 11,600), most likely arranged in a ring-like pentameric configuration and CT A consists of two non-identical polypeptide chains A or a-chain (Mr = 23,000) and A2 or γ-chain (Mr = 5,500) linked by a single disulfide bridge (for reviews see refs. 1, 3–5). CT A is synthesized as a single polypeptide chain which is “nicked” between the two cysteine residues by an extracellular bacterial protease. During this proteolysis two serine residues are removed at the COOH terminus of A1 6. The first event in the action of CT on cells is the rapid, irreversible binding to receptors on the cell surface. It is generally accepted that the receptor for the toxin is the mono-sialoganglioside GM1 (for reviews see refs. 3,4,7).
KeywordsLipid Bilayer Adenylate Cyclase Fluorescence Quenching Cholera Toxin Amino Acid Side Chain
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