alpha beta T cell receptor interactions with syngeneic and allogeneic ligands: Affinity measurements and crystallization

Cellular immunity is mediated by the interaction of an alpha beta T cell receptor (TCR) with a peptide presented within the context of a major histocompatibility complex (MHC) molecule. Alloreactive T cells have alpha beta TCRs that can recognize both self- and foreign peptide-MHC (pMHC) complexes, implying that the TCR has significant complementarity with different pMHC. To characterize the molecular basis for alloreactive TCR recognition of pMHC, we have produced a soluble, recombinant form of an alloreactive alpha beta T cell receptor in Drosophila melanogaster cells. This recombinant TCR, 2C, is expressed as a correctly paired alpha beta heterodimer, with the chains covalently connected via a disulfide bond in the C-terminal region. The native conformation of the 2C TCR was probed by surface plasmon resonance (SPR) analysis by using conformation-specific monoclonal antibodies, as well as syngeneic and allogeneic pMHC ligands. The 2C interaction with H-2K(b)-dEV8, H-2K(bm3)-dEV8, H-2K(b)-SIYR, and H-2L(d)-p2Ca spans a range of affinities from K-d = 10(-4) to 10(-6) M for the syngeneic (H-2K(b)) and allogeneic (H-2K(bm3), H-2L(d)) ligands. In general, the syngeneic ligands bind with weaker affinities than the allogeneic ligands, consistent with current threshold models of thymic selection and T cell activation. Crystallization of the 2C TCR required proteolytic trimming of the C-terminal residues of the alpha and beta chains. X-ray quality crystals of complexes of 2C with H-2K(b)-dEV8, H-2K(bm3)-dEV8 and H-2K(b)-SIYR have been grown.