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bioRxiv · 10.1101/2022.04.14.488403

Cooperative ectodomain interaction among TCRαβ, CD3γε, and CD3δε enhances TCR mechanotransduction

Yuan, Z.·Cong, P.·Natarajan, A.·Ge, C.·Travaglino, S.·Beesam, S.·Grazette, D.·Krogsgaard, M.·Zhu, C.
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Abstract

TCR signaling poses a mechanical problem: pMHC binding occurs at the TCR{beta} ectodomain (ECD) head, whereas ITAM phosphorylation occurs on CD3 cytoplasmic tails. Chemistry cannot bridge this >10 nm gap, requiring the two events to be coupled through the TCR-CD3 interface, thus involving conformational allostery and being regulatable by force. Although weak ECD cis-interactions between TCR{beta} and CD3 have been proposed to contribute to this coupling, their kinetics and mechanical competence remain elusive. Here, we quantify TCR{beta}-CD3 ECD cis-interactions in a pseudo-cis configuration using two-dimensional binding and single-bond force spectroscopy, finding that TCR{beta}-CD3{gamma}{varepsilon} and TCR{beta}-CD3{delta}{varepsilon} interactions have low affinity and rapid kinetics, yet form catch bonds. Critically, concurrent engagement of CD3{gamma}{varepsilon} and CD3{delta}{varepsilon} produces high cis-cooperativity, yielding a stronger and longer-lasting CD3{gamma}{varepsilon}-TCR{beta}-CD3{delta}{varepsilon} trimolecular catch bond than the sum of the two dimeric bonds, with force-stabilized lifetimes matching those of agonist TCR-pMHC trans-interaction. Molecular dynamics simulations reveal an expanded, cooperative, and asymmetric contact network, making CD3{delta}{varepsilon} more force-responsive and susceptible to conformational change than CD3{gamma}{varepsilon}. Interface mutations do not alter force-free affinities but remodel cooperative cis-bond profiles, leading to an inverse correlation with trans-bond profiles and T cell signaling. These results identify cooperative ECD cis-interaction as a mechanically regulatable allosteric coupling element at the TCR-CD3 junction important to antigen recognition and signal initiation.

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Yuan, Z., Cong, P., Natarajan, A., Ge, C., Travaglino, S., Beesam, S., Grazette, D., Krogsgaard, M., Zhu, C.. 2022-04-15. Cooperative ectodomain interaction among TCRαβ, CD3γε, and CD3δε enhances TCR mechanotransduction. https://doi.org/10.1101/2022.04.14.488403

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