CD3

The TCR is made up two chains (α and β, red polypeptides) which have characteristic extracellular Ig folds that are stabilized by disulfide bonds. The TCR does not have a cytosolic signaling domain. In order to couple extracellular ligand (peptide-MHC [pMHC] complexes) recognition to intracellular signaling, it constitutively associates with six polypeptides of the CD3 family—which exist as disulfide-linked dimers of CD3ε-CD3γ, CD3ε-CD3δ, CD3ζ-CD3ζ. The TCRCD3 complex is stabilized by electrostatic interactions in the membranespanning region with the positive charges on Lysine (K) and Arginine (R) in the TCR α and β chains associating with the aspartic acid (D) on the CD3 molecules. In addition, glutamic acid residue (E) on the CD3γ chain stabilizes the extended lattice like interactions to form the holocomplex. The immunoreceptor tyrosine–based activation motifs (ITAMs) on the CD3 chains are marked as blue boxes. A total of 10 ITAMs are therefore associated with the TCR complex, the largest number for any receptor unit.