Exhaustive Characterization of TCR–pMHC Binding Energy Estimated by the String Model and Miyazawa-Jernigan Matrix

Abstract

Accurate calculations of protein-protein binding free energies based on rigorous models, which consider the binding complex structure in atomic detail, are computationally expensive and impracticable to apply to T cell repertoire formation that occurs in the thymus because this process involves the interactions among numerous combinations of T cell receptors (TCRs) and presented peptides. By comparison, an evaluation of binding free-energy using a combination of the string model and Miyazawa-Jernigan matrix is very efficient and was therefore applied to estimate interaction energies between T cell receptor-peptide-MHC (TCR-pMHC) complexes, which appeared to successfully explain the effects of binding capacity of MHC on repertoire-formation and the reason for the presence of elite-controllers of some viral infections. However, this evaluation method is overly simplified and requires more detailed considerations when applied to evaluating TCR-pMHC interactions. In this study, we examined this method exhaustively and revealed the limitations of the method. Following features necessitate cautious attitude when interpreting the calculation results: first, the apparent increase in the number of hot spots in accordance with an increase of educational epitope pool size does not mean an increased TCR specificity of surviving clones; second, strong binders to any TCR converge to some limited sequences that are determined by the physical nature of the Miyazawa-Jernigan matrix.