IDENTIFICATION OF CLASS-II MAJOR HISTOCOMPATIBILITY COMPLEX AND T-CELL RECEPTOR-BINDING SITES IN THE SUPERANTIGEN TOXIC SHOCK SYNDROME TOXIN-1

Superantigens, in association with class II major histocompatibility c omplex (MHC) molecules, activate T cells bearing particular beta chain variable domains of the T cell receptor (TCR). Unlike conventional pe ptide antigens, superantigens bind as intact proteins to TCR and MHC m olecules outside their peptide binding sites. To characterize these in teractions at the molecular level, random point mutations were generat ed in the gene encoding toxic shock syndrome toxin 1, a bacterial supe rantigen associated with toxic shock syndrome. Functionally impaired m utants were identified based on their lack of murine and human T cell stimulatory activities, and experiments analyzing binding to human his tocompatibility leukocyte antigen-DR molecules differentiated residues involved in MHC from TCR binding. The results showed that the great m ajority of mutations are clustered in two distinct regions of the toxi c shock syndrome toxin 1 molecule. The class II MHC binding site is lo cated in the hydrophobic region bf the NH2-terminal domain, and the TC R binding site is primarily in the major central groove of the COOH-te rminal domain. These studies provide insight into the interactions nec essary for superantigen-mediated disease in humans.