The rotational orientation of the T cell receptor bound to peptide: MHC

The T cell receptor (TCR) is the multi-chained cell surface molecule that mediates the specific recognition of antigen by the T cell. The alpha and beta chains of the TCR are members of the immunoglobulin gene superfamily and form the antigen binding components of the TCR. Although the function of alphabeta-TCRs has been well characterized, less is known about their molecular structure. Current three-dimensional structural models of TCR are based on the similarities in primary sequence between the TCR with immunoglobulin genes. Models of the ternary structure of the TCR and MHC complex have also been proposed. These models, however, do not address the question of the rotational orientation of TCR on the peptide:MHC complex. This thesis uses molecular biological techniques to characterize the molecular interactions between TCR and the peptide:MHC complex to determine the rotational orientation. of TCR bound to the peptide:MHC complex.The well characterized CD4+ I-Ak restricted cloned T cell line, D10, and its specific ligands are used in T-cell functional response assays to identify TCR:ligand interaction sites. An analysis of the antigenic peptide by truncation and substitution of residues identify the residue in position p2 as important for interaction with TCR. Studies with MHC molecules, containing mutations at various putative TCR or peptide interaction sites identify residues in MHC alpha-chain HVR2 as an important TCR interaction site. Finally, residue 52 of the TCR alpha-chain CDR2 is mapped to peptide position p2 and MHC alpha-chain HVR2. These data are synthesized into a three-dimension ternary model of interaction between TCR, antigenic-peptide, and MHC using a computer graphics program. These results demonstrate a direct interaction between the germline encoded CDR2 of the TCR with the antigenic-peptide, which provides an explanation for why certain Valpha genes are highly correlated with certain peptide-antigens and suggests that TCR-MHC spatial interaction have stereotypic rotational orientation