A model of the molecular structure of toxin III from Anemonia sulcata.

A Chou and Fasman analysis of the Toxin III from Anemonia sulcata reveals that this short polypeptide (27 residues) probably is mostly made up of a nearly continuous beta-turn structure (7 beta-turns). This structure allows only one possible solution of disulfide bond formation (3-23, 4-17, 6-17). The resulting rigid structure has very few degrees of freedom. Molecular models indicate that one side of the molecule bearing tyr(7), trp(8), pro(25), glu(20) and lys(20) is very similar in its three-dimensional structure to that part of the molecule of variant III toxin from Centruroides sculpturatus as revealed by x-ray crystallography, bearing tyr(4), trp(47), gly(3), glu(2) and lys(1), all of which are invariant or allow only very conservative substitutions. This analysis, therefore, suggests a specific conformation for Toxin III.