Abstract
ABSTRACTThe T-cell receptor (TCR) complex comprises TCRαβ, CD3γε, CD3δε, and CD3ζζ. TCRαβ engagement with peptide-bound major histocompatibility complex (pMHC) triggers CD3 phosphorylation, which is regulated by mechanical force. However, the inner workings of the TCR mechanotransduction machinery remains unclear. TCR ectodomain (ECD) interactions have been inferred from structural and mutagenesis studies. Due to their extreme weakness, however, direct measurements of affinity had failed and of force regulation have never been attempted. Here we measured two-dimensional affinities and force-dependent lifetimes of interactions among TCRαβ, CD3γε, and CD3δε ECDs, showing a cooperative CD3δε–TCRαβ–CD3γε catch bond with longer- lasting lifetime that exceeds the TCR–pMHC bond lifetime. Molecular dynamics stimulations revealed a central interacting region surrounded by TCR ECDs and identified critical interacting residues at their interfaces. Interfering TCR ECD interactions by antibodies impaired TCR–pMHC interaction and T cell function. Mutating residues that mediate TCR ECD cis-interactions with CD3s altered the catch bond of TCR–pMHC trans-interaction, which correlates with changed T cell cytokine production. Thus, TCR mechanotransduction is supported by cooperative TCR ECD interactions, which regulates T cell function. Our results provide a missing link between pMHC ligation and CD3 signaling and may guide future TCR engineering design for immunotherapies.
Publisher
Cold Spring Harbor Laboratory