Mutation of the disulfide loop in staphylococcal enterotoxin A. Consequences for T cell recognition
Grossman, D.; Van, M.; Mollick, J.A.; Highlander, S.K.; Rich, R.R.
Journal of Immunology 147(10): 3274-3281
1991
ISSN/ISBN: 0022-1767 PMID: 1834733 Document Number: 384174
The hallmark of T cell responses to staphylococcal enterotoxins (SE) and other super-Ag is a selective stimulation of cells expressing particular TCR-V .beta. segments. Our previous studies suggested that the disulfide loop in SE is critical for their interaction with the TCR. To investigate this concept in further detail we constructed disulfide loop mutants of staphylococcal enterotoxin A (SEA), and examined these altered toxins for mitogenicity, class II MHC binding, and V.beta. specificity. We found that substitutions of either Cys-96 or Cys-106 decreased mitogenicity by 100-fold without significantly affecting class II binding or resistance of the molecule to proteolysis. Several mutants lost the capacity to stimulate V.beta.11+ cells, except a Cys-106 .fwdarw. Gln mutant for which V.beta.11-stimulatory activity was increased. By contrast, mutants containing Cys .fwdarw. Ala substitutions acquired the capacity to stimulate V.beta.6+ cells. Despite these effects on V.beta. specificity, all mutants retained the predominant preference of SEA for V.beta.3+ cells. Neither exchange of regions flanking the loop in SEA with corresponding residues in SEB, nor conversion of the entire loop region of SEA to that of SEE, were associated with transfers of V.beta. specificity. Our results suggest that the disulfide loop in SEA contributes to toxin avidity for the TCR, rather than specificity for particular V.beta.