LOW PH INDUCES A HYDROPHOBIC DOMAIN IN THE TETANUS TOXIN MOLECULE

Binding of the nonionic detergent [3H]Triton X-100 by tetanus toxin, by its fragment C and by its .alpha. chain was studied. At .gtoreq. pH 4.00, tetanus toxin does not bind Triton X-100. At pH < 4.00, binding of detergent to the toxin occurs. At pH 3.00, a maximum of 100 mol bound/mol of protein is reached only when the detergent concentration exceeds its critical micelle concentration. No measurable amount of Triton X-100 is bound by the toxin C fragment at pH 3.00. Most of the tetanus toxin .alpha. chain precipitates out in Triton X-100 at pH 3.00. Leakage of K+ from single-walled asolectin vesicles loaded with K was observed with tetanus toxin at pH < 4.00. When ganglioside GD1b was present on the asolectin vesicles, release of K+ was obtained with tetanus toxin between pH 4.00 to 5.00. As for diphtheria toxin, entry of tetanus toxin into an acidic compartment of target cells might be required for the expression of its biological activity.