 Mutagenesis studies with SEA have indicated that both binding sites are required for optimal T-cell activation.These studies containing TSST-1 indicate that the TCR binding domain lies at the top of the back side of this toxin, though the complete interaction remains to be determined.There have also been indications that the TCR binding site of TSST-1 is mapped to the major groove of the central alpha helix or the short amino terminal alpha helix.