Alanine scanning mutagenesis of an αβ T cell receptor:: Mapping the energy of antigen recognition

The T cell receptor (TCR) from the alloreactive T lymphocyte 2C recognizes a nonamer peptide QL9 complexed with the MHC class I molecule H2-L-d. Forty-two single-site alanine substitutions of the 2C TCR were analyzed for binding to QL9/L-d and anti-TCR antibodies. The results provided a detailed energy map of T cell antigen recognition and indicated that the pMHC and clonotypic antibody epitopes on the TCR were similar. Although residues in each V alpha and V beta CDR are important in binding pMHC, the most significant energy for the TCR/QL9/L-d interaction was contributed by CDRs 1 and 2 of both alpha and beta chains. The extent to which the individual energy contributions are directed at class I helices or peptide was also assessed.