Enhancement of diphtheria toxin potency by replacement of the receptor binding domain with tetanus toxin C-fragment: A potential vector for delivering heterologous proteins to neurons

This study describes the expression, purification, and characterization of a recombinant fusion toxin, DAB(389)TTC, composed of the catalytic and memb rane translocation domains of diphtheria toxin (DAB(389)) linked to the rec eptor binding fragment of tetanus toxin (C-fragment). As determined by its ability to inhibit cellular protein synthesis in primary neuron cultures, D AB(389)TTC was similar to 1,000-fold more cytotoxic than native diphtheria toxin or the previously described fusion toxin, DAB(389)MSH. The cytotoxic effect of DAB(389)TTC on cultured cells was specific toward neuronal-type c ells and was blocked by coincubation of the chimeric toxin with tetanus ant itoxin. The toxicity of DAB(389)TTC, like that of diphtheria toxin, was dep endent on passage through an acidic compartment and ADP-ribosyltransferase activity of the DAB(389) catalytic fragment. These results suggest that a c atalytically inactive form of DAB(389)TTC may be useful as a nonviral vehic le to deliver exogenous proteins to the cytosolic compartment of neurons.