Functional mapping of the orientation for TCR recognition of an H2-K^b-restricted ovalbumin peptide suggests that the β-chain subunit can dominate the determination of peptide side chain specificity

T cells recognize a complex of antigenic peptide bound to the class I or class II products of the MHC. Crystallographic analysis of the interaction between MHC class I-bound peptide fragments and specific TCR have recently been described and highlight the importance of the CDR3 in determining peptide specificity. The results presented here show functional data for TCR recognition of the H2-K^b class-I restricted determinant derived from OVA (SIINFEKL) that are consistent with the TCR orientation defined by these crystal structures. In addition, we also found that the β-chain CDR3 dominates side chain specificity for the most exposed regions within this peptide. The data also suggest that this orientation and pattern of β-chain dominance may extend to the recognition of a second H2-K^b-restricted peptide from the herpes simplex virus type 1 glycoprotein B (SSIEFARL), which shares a common α-chain contact with the OVA peptide. These results are discussed in terms of a common orientation for TCR-ligand interaction and the greater potential for TCR β-chain CDR3 diversity in determining peptide side chain specificity.