The structure of the T cell receptor (TCR)/CD3 complex

The TCR is made up of two disulfide-linked chains, alpha and beta, (or gamma and delta); the CD3 complex consists of five polypeptides, one each of gamma and delta, two of epsilon, and a disulfide-linked homodimer of two zeta chains [zeta]₂, or a heterodimer of zeta and eta (shown here). The carboxyl termini of these proteins are intracytoplasmic. ZAP-70 and fyn are tyrosine kinases important in T cell activation.