The guanidinium toxin binding site on the sodium channel.

Study of TTX and STX toxins and their interaction with cloned Na channels has led to a molecular model of the toxins' binding site. This model is able to explain isoform differences in binding affinity, allowing prediction of the structures of toxin-resistant channels. It provides an example of a detailed drug binding site that could serve as an example for drug engineering to improve affinity and specificity. The model has also suggested important molecular characteristics of the channel's permeation path, providing a wealth of ideas for study of this fundamental biophysical process at the molecular level. The model of the TTX and STX binding site outlines an approach to resolution of molecular structure and of certain structure-function relationships, and experimentation provoked by the model will assist in improving it.