STRUCTURAL BASIS FOR THE INTERACTION OF SUPERANTIGEN WITH THE ALTERNATIVE SUPERANTIGEN-BINDING RECEPTOR P85

Superantigens are microbial products which bind both to the TCR beta-c hain and, with moderate affinity, to MHC class II molecules. Class II- bearing cells bind the superantigen and present the superantigen to T cells expressing certain TCR beta-chain variable region alleles. We ha ve previously reported that the superantigen staphylococcal enterotoxi n B (SEE) binds with moderate affinity to the protein p85 expressed on COS-1, an African Green Monkey kidney fibroblast-like cell line. In t he present report we carry out a structural analysis to examine the ba sis for the interaction of superantigen to p85. We show that SEC1, SEC 2, and SEC3 also bind to p85 based on inhibition of the binding of rad iolabeled SEE. On the other hand? SEA, SED, SEE and toxic shock syndro me toxin-l do not exhibit detectable binding. In an effort to characte rize the structural basis for the SEE binding to p85, we have generate d both amino- and carboxy-terminal truncations of SEE expressed as fus ion proteins with the maltose-binding protein of Escherichia coil. Our results show that the full-length SEE fusion protein and a truncation missing the 81 amino-terminal amino acids both compete successfully w ith native SEE for binding. On the other hand, carboxy-terminal trunca tions in which 19 or 34 residues are deleted both fail to compete for binding. These results are consistent with results which show that mon oclonal anti-SEE antibodies specific for carboxy-terminal determinants block SEE binding to p85, but an amino-terminal mAb fails to exhibit any alteration in binding. These results suggest that residues at or n ear the carboxy-terminus of SEE play a role in binding to p85. (C) 199 7 Elsevier Science Ltd.