The impact of single amino acid substitutions in CD3gamma on the CD3epsilongamma interaction and T-cell receptor-CD3 complex formation.

The human T-cell receptor-CD3 complex consists of at least eight polypeptide chains; CD3gamma- and delta-dimers associate with the disulfide linked alphabeta- and zetazeta-dimers to form a functional receptor complex. The exact structure of this complex is still unknown. We now have examined the interaction between CD3gamma and CD3 in human T-cells. For this purpose, we have generated site-directed mutants of CD3gamma that were introduced in human T-cells defective in CD3gamma expression. Cell-surface and intracellular expression of the introduced CD3gamma chains was determined, as was the association with CD3delta, CD3, and the T-cell receptor. Although the introduction of wild type CD3gamma and CD3gamma (78Y-F) fully restored T-cell receptor assembly and expression, the introduction of CD3gamma (82C-S), CD3gamma (85C-S), and CD3gamma (76Q-E) all resulted in an impaired association between CD3gamma and CD3 and a lack of cell-surface expressed CD3gamma. Finally, the introduction of CD3gamma (76Q-L) and CD3gamma (78Y-A) restored the expression of TCR-CD3deltagammazeta2 complexes, although the association between CD3gamma and CD3 was impaired. These results indicate that several amino acids in CD3gamma are essential for an optimal association between CD3gamma and CD3 and the assembly of a cell-surface expressed TCR-CD3deltagammazeta2 complex.