MHC class I H-2L(d) complexed with peptide QL9 (or p2Ca) is a high- affinity alloantigen for the 2C TCR. We used the crystal structure of H- 2L(d) with a mixture of bound peptides at 3.1 A to construct a model of the allogeneic 2C-L(d)/QL9 complex for comparison with the syngeneic 2C-K(b)/dEV8 structure. A prominent ridge on the floor of the L(d) peptide-binding groove, not present in K(b), creates a C-terminal bulge in L(d) peptides that greatly increases interactions with the 2C β-chain. Furthermore, weak electrostatic complementarity between Asp77 on the α1 helix of K(b) and 2C is enhanced in the allogeneic complex by closer proximity of QL9 peptide residue AspP8 to the 2C HV4 loop.
Speir, J. A., Garcia, K. C., Brunmark, A., Degano, M., Peterson, P. A., Teyton, L., & Wilson, I. A. (1998). Structural basis of 2C TCR allorecognition of H-2L(d) peptide complexes. Immunity, 8(5), 553–562. https://doi.org/10.1016/S1074-7613(00)80560-9