Clustering of the ζ-Chain Can Initiate T Cell Receptor Signaling

T cell activation is initiated when ligand binding to the T cell receptor (TCR) triggers intracellular phosphorylation of the TCR-CD3 complex. However, it remains unknown how biophysical properties of TCR engagement result in biochemical phosphorylation events. Here, we constructed an optogenetic tool that induces spatial clustering of zeta -chain in a light controlled manner. We showed that spatial clustering of the zeta -chain intracellular tail alone was sufficient to initialize T cell triggering including phosphorylation of zeta -chain, Zap70, PLC gamma, ERK and initiated Ca2+ flux. In reconstituted COS-7 cells, only Lck expression was required to initiate zeta -chain phosphorylation upon zeta -chain clustering, which leads to the recruitment of tandem SH2 domain of Zap70 from cell cytosol to the newly formed zeta -chain clusters at the plasma membrane. Taken together, our data demonstrated the biophysical relevance of receptor clustering in TCR signaling.