TCR-pMHC complex formation triggers CD3 dynamics

Abstract

The mechanism of T cell triggering upon engagement with a peptide-MHC (pMHC) complex remains a challenging problem. In order to observe structural and dynamics changes in the T cell receptor (TCR) upon pMHC binding, we carried out coarse grained molecular dynamics simulations of TCR-only and TCR-pMHC systems starting from a recently solved cryo-EM structure of the TCR and CD3 co-receptors. The simulations were performed in biological membranes for an aggregated length of 2 ms. We observed that, while unengaged TCRs adopted conformations that bent and restricted the dynamics of the CD3 co-receptors, the pMHC-bound TCRs adopted elongated conformations that allowed CD3 co-receptors to diffuse more freely. In this way, the TCR-pMHC pair acted as a "drawbridge", licensing the dynamics of the CD3 co-receptors, resulting in signal transmission across the plasma membrane.