Structural Model of the Extracellular Assembly of the TCR-CD3 Complex

• CD3γε and CD3δε can individually bind to the TCR to yield a two-sided binding model
• CD3γε binds to the TCR β subunit and CD3δε binds to the TCR α subunit
• The molecular basis of TCR-CD3 interactions is examined through NMR spectroscopy
• The extracellular TCR-CD3 structure is revealed using computational docking

SummaryAntigen recognition of peptide-major histocompatibility complexes (pMHCs) by T cells, a key step in initiating adaptive immune responses, is performed by the T cell receptor (TCR) bound to CD3 heterodimers. However, the biophysical basis of the transmission of TCR-CD3 extracellular interaction into a productive intracellular signaling sequence remains incomplete. Here we used nuclear magnetic resonance (NMR) spectroscopy combined with mutational analysis and computational docking to derive a structural model of the extracellular TCR-CD3 assembly. In the inactivated state, CD3γε interacts with the helix 3 and helix 4-F strand regions of the TCR Cβ subunit, whereas CD3δε interacts with the F and C strand regions of the TCR Cα subunit in this model, placing the CD3 subunits on opposing sides of the TCR. This work identifies the molecular contacts between the TCR and CD3 subunits, identifying a physical basis for transmitting an activating signal through the complex.

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