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The binding of TCRs to their peptide-MHC ligands is characterized by a low affinity, slow kinetics, and a high degree of cross-reactivity. Here, we report the results of a kinetic and thermodynamic analysis of two TCRs binding to their peptide-MHC ligands, which reveal two striking features. First, significant activation energy barriers must be overcome during both association and dissociation, suggesting that conformational adjustments are required. Second, the low affinity of binding is a consequence of highly unfavorable entropic effects, indicative of a substantial reduction in disorder upon binding. This is evidence that the TCR and/or peptide-MHC have flexible binding surfaces that are stabilized upon binding. Such conformational flexibility, which may also be a feature of primary antibodies, is likely to contribute to cross-reactivity in antigen recognition.

Type

Journal article

Journal

Immunity

Publication Date

03/1999

Volume

10

Pages

357 - 365

Keywords

Animals, Binding Sites, Entropy, Evolution, Molecular, HLA-A2 Antigen, Humans, Kinetics, Mice, Oligopeptides, Protein Binding, Protein Conformation, Receptors, Antigen, Receptors, Antigen, T-Cell, Temperature, Viral Proteins