Specificity and Binding Properties of a Single-chain T Cell Receptor

Abstract

The specificity of a T cell is dictated by an α β T cell receptor (TCR) that recognizes a complex of peptide and a product of the major histocompatibility complex (MHC). Recent studies have begun to characterize the affinities and kinetics of these interactions, but details of the α β TCR structure and function are not known. To examine some of these issues, we focus in this report on a TCR derived from the T cell clone 2C. This TCR binds to a complex of the nonapeptide QL9 and the class I MHC product L dwith the highest affinity of any known TCR/ligand interaction ( K D∼10 −7M). Circular dichroism showed that a single-chain TCR (scTCR) containing linked V α and V β regions from T cell 2C and refolded from Escherichia coliinclusion bodies exhibited the characteristic β-sheet structure of immunoglobulins. A sensitive assay that is capable of detecting the interaction of soluble scTCR with peptide/MHC ligand on the surface of target cells was used to demonstrate that the peptide specificity of this scTCR reflects that of the TCR found on the surface of 2C. Analysis of several scTCR V α region mutants confirmed that the V α domain is critical for the specificity of scTCR binding. Finally, we identified some notable differences in the complementarity determining regions (CDR) of the 2C TCR compared to the CDR of previously characterized, cytochrome- specific TCR. These differences are discussed in the light of what is known about antibody binding sites, the high affinity of the 2C TCR, and the nature of the residues on QL9 that are predicted to interact with the TCR.