Analysis of the interaction site for the self superantigen Mls-1a on T cell receptor Vβ

Abstract

Superantigen bound to major histocompatibility complex (MHC) products have been shown to stimulate T cells in a Vβ-specific manner. Mouse T cells bearing Vβ8.1 usually respond to the self superantigen, Mls-1a, whereas T cells bearing Vβ8.2a do not. Previously, using site-directed mutational analysis, we identified the residues of natural variants of T cell receptor (TCR) Vβ8.2 that conferred Mls-1a reactivity. These residues are predicted to lie on a β-pleated sheet of the TCR Vβ element, well away from the expected binding site for antigen and MHC proteins. This study was undertaken to determine the effect of glycosylation on this β-pleated sheet on Mls-1a reactivity and to map the extent of the interaction site on Vβ8.2 for Mls-1a. A panel of T cell hybridomas expressing mutant Vβ8.2 elements were tested for their responses to Mls-1a, as well as to peptides derived from the conventional protein antigen, chicken ovalbumin. Here we demonstrate that first, N-linked carbohydrate on the lateral surface of Vβ blocks the interaction of the TCR Vβ with the self superantigen, Mls-1a, but has no effect on the TCR interaction with peptide antigen and MHC, second, that the interaction site for Mls-1a extends over the surface of the solvent-exposed β-pleated sheet on the side of the TCR, and third, that mutations which affect both superantigen and peptide antigen reactivity lie at the beginning of the first complementarity determining region of Vβ, consistent with models of the trimolecular complex of TCR-peptide-MHC.