A MUTATION AT GLYCINE RESIDUE-31 OF TOXIC SHOCK SYNDROME TOXIN-1 DEFINES A FUNCTIONAL SITE CRITICAL FOR MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II BINDING AND SUPERANTIGENIC ACTIVITY

Random mutagenesis with hydroxylamine was done on toxic shock syndrome toxin-1 (TSST-1) to identify the amino acid residues critical for bin ding to major histocompatibility complex (MHC) class II molecules of h uman monocytes. A double mutant with amino acid substitutions of glyci ne 31-->arginine and aspartic acid 184-->asparagine (G31R.D184N) demon strated markedly reduced binding to human monocytes and induction of m itogenesis or cytokine secretion. Site-directed mutagenesis revealed t hat G31R, but not D184N, was at least 4 orders of magnitude less activ e than wild type recombinant (r) TSST-1 in these biologic activities a nd did not induce lethal shock in mice. The global structure of G31R r emained highly similar to wild type rTSST-1 as evidenced by circular d ichroism spectroscopy and binding to anti-TSST-1 polyclonal and monocl onal antibodies. These studies identified TSST-1 residue 31 as critica l for binding to MHC class II molecules and for the consequent superan tigenic and lethal properties of TSST-1.