The Y105 phosphosite between the SH3.1 and SH3.2 domains of Nck1 regulates its binding to CD3ϵ.

In αβ T cells, ligand binding to T cell receptor (TCR) triggers conformational changes at CD3ε subunits to expose the proline-rich sequence (PRS), which binds to the non-catalytic region of tyrosine kinase (Nck) via its Src homology 3 (SH3).1 domain. Recruitment of Nck to CD3ε initiates phosphorylation of various signaling proteins that activate T cells. However, the mechanisms by which Nck associates with and dissociates from the TCR remain poorly understood. This study identifies the tyrosine 105 (Y105) phosphosite between the SH3.1 and SH3.2 domains of Nck1 that regulates the Nck1-CD3ϵ association. Notably, a Y105 mutation resulted in prolonged association of Nck1 with TCR, impaired the phosphorylation of CD3ε, TCRζ, ζ-chain-associated protein kinase 70, and extracellular signal-regulated kinase 1/2, and abrogated the recruitment of lymphocyte-specific kinase (Lck) to TCR. These findings revealed the function of Y105 as a molecular switch that controls the assembly and disassembly of Nck1 and CD3ε.