Structural comparison of α/β and γ/δ T cell receptor-CD3 complexes reveals identical subunit interactions but distinct cross-linking patterns of T cell receptor chains

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Abstract
Here we compare the subunit interactions within the α/β and γ/δ T cell receptor‐CD3 (TcR‐CD3) complexes. By using different detergent solubilization protocols, subunit interactions can be defined within such cell surface receptor complexes. It was found that in both TcR‐CD3 complexes analogous subunit interactions can be defined: CD3γ and CD3δ each form a stable complex with separate CD3ε chains. Both the TcRγ/δ and TcR α/β form stable receptor complexes with these CD3 γ/ε and CD3 δ/ε subunits. A ζ homodimer is present in these TcR‐CD3 complexes. However, biochemical cross‐linking results in a covalent bond between the CD3γ chain and the TcRβ chain in α/β TcR‐CD3 complexes and between the CD3γ chain and the TcRδ in γ/δ TcR‐CD3 complexes. This latter observation was independent of the type of TcR γ/δ studied (e.g. disulfide or non‐disulfide linked). These cross‐linking results either indicate that the TcR β and δ chains are each others structural homolog or that in TcR‐CD3 complexes both TcR chains (α and β, γ and δ) are spatially closely associated with the CD3γ chain. The identical subunit interactions in the α/β and γ/δ TcR‐CD3 complexes indicate no large structural differences between these receptor complexes but rather suggest a striking conservation of crucial interaction between subunits in the TcR‐CD3 complexes.