Structural basis for HLA-DQ binding by the streptococcal superantigen SSA.
Streptococcal superantigen (SSA) is a 28,000 Mr toxin originally isolated from a pathogenic strain of Streptococcus pyogenes that has 60% sequence identity with staphylococcal enterotoxin B (SEB). SSA and SEB, however, do not compete for binding on the surfaces of cells expressing MHC class II molecules. This behavior had been ascribed to SSA and SEB binding to distinct sites on, or different subsets of, HLA-DR molecules. Here we demonstrate that SSA binds predominantly to HLA-DQ, rather than to HLA-DR molecules, and present the crystal structure of SSA at 1.85 A resolution. These data provide a structural basis for interpreting the interaction of SSA with HLA-DQ molecules as well as a foundation for understanding bacterial superantigen affinities for distinct MHC isotypes.
Sundberg
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Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
Jardetzky
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D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000276:immunology*; D018360:Crystallography, X-Ray; D006683:HLA-DQ Antigens / Q000737:chemistry / Q000276:immunology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011994:Recombinant Proteins / Q000737:chemistry / Q000276:immunology; D017386:Sequence Homology, Amino Acid; D013297:Streptococcus pyogenes / Q000276:immunology*
D000942:Antigens, Bacterial; D006683:HLA-DQ Antigens; D011994:Recombinant Proteins; C117321:streptococcal superantigen SSA