Abstract
Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are structurally similar AB5-type protein toxins. They move from the cell surface to the endoplasmic reticulum where the A1 catalytic subunit is separated from its holotoxin by protein disulfide isomerase (PDI), thus allowing the dissociated A1 subunit to enter the cytosol for a toxic effect. Despite similar mechanisms of toxicity, CT is more potent than LT. The difference has been attributed to a more stable domain assembly for CT as compared to LT, but this explanation has not been directly tested and is arguable as toxin disassembly is an indispensable step in the cellular action of these toxins.
Highlights
Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are structurally similar AB5-type protein toxins
We show that protein disulfide isomerase (PDI) disassembles CT more efficiently than LT, and this correlates with the greater cellular potency of CT in comparison to LT
CT and LT differ in toxicity and PDI‐driven toxin disassembly but not overall stability
Summary
Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are structurally similar AB5-type protein toxins. Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are A B5-type protein toxins that share ~ 82% amino acid sequence identity and a common toxicity m echanism[1,2]. They are composed of a receptor-binding pentamer of B subunits (B5) and an A subunit (Fig. 1). The A2 chain runs as a continuous α-helix down to the orifice of the B5 central opening and threads through the pore Despite these common conformational features, significant structural differences have been reported for the C-terminal tails of the A2 subunits of LT and CT. The last four or five amino acids of the A2 subunit are missing in these structures because of poor electron density
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