Dissociation of cholera toxin functional regions after interaction with vesicles containing ganglioside G M1

Abstract

immunoelectron microscopy have provided evidence that the latent period may represent the time required for a redistribution of the toxin-receptor complexes in the cell membrane [ 10,111. Whether the active functional region penetrates the membrane through channels [ 121 or a change in the conformation of the toxin [ 131, resulting from the mobility of the toxin--s1 complexes in the membrane, remains to be determined. At present, although some authors have reported an interaction of hydrophobic nature between protomer A and membranes [13,14], no direct evidence of the dissociation either of protomer A or of the (Y chain has been obtained, after binding of the toxin to biological membranes. In view of these observations, we examined the characteristic and specific binding of cholera toxin to vesicles containing GM1 [15] with respect to the possible interactions of the active (Y fragment with model membranes. The effect of binding on the reactivity of the interchain disulfide bond connecting the Q! and 7pS functional regions was also studied. This communication shows that the interaction of cholera toxin with GM1--vesicles is strong enough to induce perturbations in the lipid membrane but it does not affect the dissociation of the active (Y chain from the vesicle-bound toxin.