Influence of the NH2-terminal Amino Acid of the T Cell Receptor α Chain on Major Histocompatibility Complex (MHC) Class II + Peptide Recognition

The α/β T cell receptor (TCR) recognizes peptide fragments bound in the groove of major histocompatibility complex (MHC) molecules. We modified the TCR α chain from a mouse T cell hybridoma and tested its ability to reconstitute TCR expression and function in an α chain–deficient variant of the hybridoma. The modified α chain differed from wild type only in its leader peptide and mature NH2-terminal amino acid. Reconstituted cell surface TCR complexes reacted normally with anti-TCR and anti-CD3 antibodies. Although cross-linking of this TCR with an antibody to the TCR idiotype elicited vigorous T cell hybridoma activation, stimulation with its natural MHC + peptide ligand did not. We demonstrated that this phenotype could be reproduced simply by substituting the glutamic acid (E) at the mature NH2 terminus of the wild type TCR α chain with aspartic acid (D). The substitution also dramatically reduced the affinity of soluble α/β-TCR heterodimers for soluble MHC + peptide molecules in a cell-free system, suggesting that it did not exert its effect simply by disrupting TCR interactions with accessory molecules on the hybridoma. These results demonstrate for the first time that amino a