ROLE OF CD3-GAMMA IN T-CELL RECEPTOR ASSEMBLY

The T cell receptor (TCR) consists of the Ti alpha beta heterodimer an d the associated CD3 gamma delta epsilon and zeta(2) chains. The struc tural relationships between the subunits of the TCR complex are still not fully known. In this study we examined the role of the extracellul ar (EC), transmembrane (TM), and cytoplasmic (CY) domain of CD3 gamma in assembly and cell surface expression of the complete TCR in human T cells. A computer model indicated that the EC domain of CD3 gamma fol ds as an Ig domain. Based on this model and on alignment studies, two potential interaction sites were predicted in the EC domain of CD3 gam ma. Site-directed mutagenesis demonstrated that these sites play a cru cial role in TCR assembly probably by binding to CD3 epsilon. Mutagene sis of N-linked glycosylation sites showed that glycosylation of CD3 g amma is not required for TCR assembly and expression. In contrast, tre atment of T cells with tunicamycin suggested that N-linked glycosylati on of CD3 delta is required for TCR assembly. Site-directed mutagenesi s of the acidic amino acid in the TM domain of CD3 gamma demonstrated that this residue is involved in TCR assembly probably by binding to T i beta. Deletion of the entire CY domain of CD3 gamma did not prevent assembly and expression of the TCR. In conclusion, this study demonstr ated that specific TCR interaction sites exist in both the EC and TM d omain of CD3 gamma. Furthermore, the study indicated that, in contrast to CD3 gamma, glycosylation of CD3 delta is required for TCR assembly and expression.