LOCALIZATION OF BINDING-SITES OF STAPHYLOCOCCAL-ENTEROTOXIN-B (SEB), A SUPERANTIGEN, FOR HLA-DR BY INHIBITION WITH SYNTHETIC PEPTIDES OF SEB

Staphylococcal enterotoxins are major causes of food poisoning and tox ic shock syndrome. Their ability to bind to major histocompatibility c omplex (MHC) class II molecules has been suggested to be the first ste p in the mechanism whereby they cause illness. By flow cytometric anal ysis, the sites of interaction of staphylococcal enterotoxin B (SEB) w ith HLA-DR molecules were probed in the present study by inhibiting th e binding of biotinylated SEB to a human T-cell line (HUT-78) with syn thetic peptides of SEB. Five peptides of SEB gave significant inhibiti on of binding: a peptide containing amino acids 9 to 20 [SEB(9-20)], S EB(30-38), SEB(61-70), SEB(90-114), and SEB(169-181). One peptide, SEB (39-51), enhanced binding, Among the inhibitory peptides, SEB(90-114), a peptide spanning the entire disulfide loop, showed the most efficie nt inhibition of binding. Peptides SEB(9-20) and SEB(39-51) include am ino acid residues that have been identified by previous mutation studi es (J.W. Kappler, A. Herman, J. Clements, and P. Marrack, J. Exp. Med. 175:387-396, 1992) as being important in binding to MHC class II. Ami no acids lining the alpha 5 groove of SEB have also been postulated to be involved in binding to MHC class LT molecules. However, only two o f the residues that line the alpha 5 groove of SEB, His-12 and Tyr-17, are on peptide SEB(9-20) that inhibits binding. These results confirm previous studies that implicated the amino-terminal portion of the mo lecule in binding to MHC class II molecules and further indicate an im portant role for residues in other regions, particularly the disulfide loop.