title: Defining a novel domain of staphylococcal toxic shock syndrome toxin-1 critical for major histocompatibility complex class II binding, superantigenic activity, and lethality.
abstract: Staphylococcal toxic shock syndrome toxin-1 (TSST-1) is implicated in the pathogenesis of superantigen-mediated shock. We previously identified TSST-1 residues G31/S32 to be important for major histocompatibility complex (MHC) class II binding, as well as superantigenic and lethal activities. However, the site-directed TSST-1 mutant toxin, G31R, could still induce mitogenesis and low-level TNF alpha secretion, suggesting that additional MHC class II binding sites other than G31/S32 may exist. In the current study, a TSST-1-neutralizing monoclonal antibody, MAb5, was found to inhibit TSST-1 binding to human peripheral blood mononuclear cells, neutralize TSST-1-induced mitogenesis and cytokine secretion, and protect against TSST-1-induced lethality in vivo. Epitope mapping revealed that MAb5 bound to TSST-1 residues 51-56 (T(51-56); 51YYSPAF56). Peptide T(51-56) was synthesized and found to also inhibit TSST-1 binding to human monocytes as well as TSST-1-induced mitogenesis, cytokine secretion, and lethality in vivo. This T(51-56) epitope, located within the beta 3/beta 4 loop, and the previously identified G31/S32 epitope, within the beta 1/beta 2 loop of TSST-1, are separated within the primary sequence, but spatially juxtaposed to each other. Collectively, these findings suggest that a discontinuous epitope comprising of regions within both the beta 1/beta 2 and beta 3/beta 4 loops, are critical for MHC class II binding, and the consequent superantigenic and lethal activities of TSST-1.
authors.affiliation: Department of Medicine, University of British Columbia, Vancouver, Canada.
authors.forename: W W
authors.initials: WW
authors.lastname: Kum
authors.forename: K B
authors.initials: KB
authors.lastname: Laupland
authors.forename: A W
authors.initials: AW
authors.lastname: Chow
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000096:biosynthesis / Q000378:metabolism; D001427:Bacterial Toxins; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D004768:Enterotoxins / Q000737:chemistry / Q000378:metabolism*; D018604:Epitope Mapping; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008938:Mitosis; D008958:Models, Molecular; D009000:Monocytes / Q000166:cytology / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011817:Rabbits; D012772:Shock, Septic / Q000139:chemically induced / Q000401:mortality; D013211:Staphylococcus aureus / Q000378:metabolism*; D018089:Superantigens / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D001427:Bacterial Toxins; D016207:Cytokines; D004768:Enterotoxins; D000949:Histocompatibility Antigens Class II; D010446:Peptide Fragments; D018089:Superantigens; C030107:enterotoxin F, Staphylococcal