Role of CD3γ in T cell receptor assembly

Abstract

The T cell receptor (TCR) consists of the Tiαβ heterodimer and the associated CD3γδε and ζ2 chains. The structural relationships between the subunits of the TCR complex are still not fully known. In this study we examined the role of the extracellular (EC), transmembrane (TM), and cytoplasmic (CY) domain of CD3γ in assembly and cell surface expression of the complete TCR in human T cells. A computer model indicated that the EC domain of CD3γ folds as an Ig domain. Based on this model and on alignment studies, two potential interaction sites were predicted in the EC domain of CD3γ. Site-directed mutagenesis demonstrated that these sites play a crucial role in TCR assembly probably by binding to CD3ε. Mutagenesis of N-linked glycosylation sites showed that glycosylation of CD3γ is not required for TCR assembly and expression. In contrast, treatment of T cells with tunicamycin suggested that N-linked glycosylation of CD3δ is required for TCR assembly. Site-directed mutagenesis of the acidic amino acid in the TM domain of CD3γ demonstrated that this residue is involved in TCR assembly probably by binding to Tiβ. Deletion of the entire CY domain of CD3γ did not prevent assembly and expression of the TCR. In conclusion, this study demonstrated that specific TCR interaction sites exist in both the EC and TM domain of CD3γ. Furthermore, the study indicated that, in contrast to CD3γ, glycosylation of CD3δ is required for TCR assembly and expression.