Identification of two binding sites in staphylococcal enterotoxin B that confer specificity for TCR V beta gene products.
The enterotoxins produced by Staphylococcus aureus are potent mitogens. They stimulate T cells in an oligoclonal fashion that is dependent on the expression of particular variable region gene elements in the beta-chain of the TCR (V beta). The fourth hypervariable loop of the TCR beta-chain is generally regarded as the site of contact for both viral and microbial superantigens. Recently, residues 60 and 61 of staphylococcal enterotoxin B (SEB) have been highlighted as central to the interaction of this toxin with the TCR. We have, therefore, analysed a series of toxins with mutations at these positions to investigate how amino acid substitutions affect the ability of mutant toxins to stimulate both human and mouse T cells. Each of the variant toxins induced proliferation in a murine V beta 8.3 T cell clone, whereas a V beta 8.1 T cell clone only responded to native toxin. A panel of nine human T cell clones expressing six different V beta elements, all of which responded to native SEB, was tested for reactivity to the variant toxins. Only one V beta 19.1+ T cell clone was found to be sensitive to substitution at positions 60 and 61 in a manner analogous to the murine V beta 8.1 T cell clone. Semi-quantitative analysis of the TCR V beta expression of human T cell lines expanded with native and mutant SEB revealed that none of the variant toxins could stimulate T cells that expressed V beta 19.1. Taken together, these results suggest that the interaction of mouse V beta 8.1 and human V beta 19.1 TCRs with SEB differs from other TCRs. Sequence comparisons of the different TCR V beta chains indicated that residues in the second complementarity determining region (CDR2) interact with the 60-61 loop of SEB. Therefore, a minimum of two distinct binding modules confer specificity to the interaction of the TCR with SEB.
Hayball
J D
JD
Department of Immunology, St Mary's Hospital Medical School, Imperial College of Science, Technology and Medicine, London, UK.
Robinson
J H
JH
O'Hehir
R E
RE
Verhoef
A
A
Lamb
J R
JR
Lake
R A
RA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002999:Clone Cells; D004768:Enterotoxins / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D008213:Lymphocyte Activation; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000378:metabolism*; D018089:Superantigens / Q000737:chemistry* / Q000235:genetics
D004768:Enterotoxins; D016693:Receptors, Antigen, T-Cell, alpha-beta; D018089:Superantigens; C031818:enterotoxin B, staphylococcal