Neuronal binding of tetanus toxin compared to its ganglioside binding fragment (Hc)

The non-toxin 50 kD C-terminus peptide of the heavy chain of tetanus Hc contains the ganglioside binding domain of tetanus toxin (TTX). Hc retains much of the capacity of tetanus toxin for binding internalization and transport by neurons. For this reason tetanus Hc has been studied as a vector for delivery of therapeutic proteins to neurons. We directly compared Hc and TTX in the capacity to bind and be internalized by neurons by ELISA. Primary cultures of dissociated fetal cortical neurons were incubated with equimolar amounts of TTX or Hc. Neuronal associated tetanus protein was 4–8 fold greater on a molar basis with tetanus toxin compared to Hc (1 h incubation). This increase in neuronal tetanus protein was evident with incubation in concentrations from 0.1 µM to 2 µM. There were greater amounts of TTX delivered to the cultured cells at both 0 °C (representing membrane bound tetanus protein) and 37 °C (bound and internalized tetanus protein). Unlike Hc, TTX showed significant continued accumulation of protein with increasing incubation durations. Neuronal associated TTX increased 2–3 fold over incubation times ranging from 1 to 8 h. Tetanus toxin appears to be clearly superior to the ganglioside binding fragment (Hc) in the capacity for neuronal binding and internalization. Atoxic tetanus proteins containing additional molecular domains as well as Hc may be more suitable vectors for linkage with therapeutic proteins and delivery to neurons. Copyright © 1999 John Wiley & Sons, Ltd.