The antigenic structure of a scorpion toxin.

Scorpion toxins constitute a family of homologous proteins that exert potent pharmacological effects on ion channels. These proteins are immunogenic and constitute a good model for investigation of the molecular basis of antigenicity. In the first part of this article we summarize the results we have obtained in recent years concerning the location of the main antigenic regions of a model toxin, toxin II of the North African scorpion Androctonus australis Hector. Then, thanks to the recently available atomic coordinates of this toxin, we analyzed the relationships between the structural features of the protein and the location of the antigenic regions: we found that antigenic regions are located at exposed parts of the molecular surface, i.e. in reverse turns and the alpha-helix. These surface parts also correspond to segments of the polypeptide chain which are most accessible to a large spherical probe modelizing an antibody molecule. Finally, we obtained a general idea of what could be the main discontinuous antigenic determinants by looking for the neighboring relationships between the most exposed residues of the protein.