Structural comparison of alpha/beta and gamma/delta T cell receptor-CD3 complexes reveals identical subunit interactions but distinct cross-linking patterns of T cell receptor chains.

Here we compare the subunit interactions within the alpha/beta and gamma/delta 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: CD3 gamma and CD3 delta each form a stable complex with separate CD3 epsilon chains. Both the TcR gamma/delta and TcR alpha/beta form stable receptor complexes with these CD3 gamma/epsilon and CD3 delta/epsilon subunit. A zeta homodimer is present in these TcR-CD3 complexes. However, biochemical cross-linking results in a covalent bond between the CD3 gamma chain and the TcR beta chain in alpha/beta TcR-CD3 complexes and between the CD3 gamma chain and the TcR delta in gamma/delta TcR-CD3 complexes. This latter observation was independent of the type of TcR gamma/delta studied (e.g. disulfide or non-disulfide linked). These cross-linking results either indicate that the TcR beta and delta chains are each others structural homolog or that in TcR-CD3 complexes both TcR chains (alpha and beta, gamma and delta) are spatially closely associated with the CD3 gamma chain. The identical subunit interactions in the alpha/beta and gamma/delta 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.