CD3 has been classified into CD3γ, δ, ε and ζ chains. The sequence and structural homology of the human and mouse CD3γ, CD3δ and CD3ε genes, and their chromosomal proximity suggested that they arose by duplication of a common ancestral gene.
Glycosylation sites are present in the extracellular domain of the CD3γ and δ chains, but not in the extracellular domain of the ε chain.
The CD3γ, δ and ε
chains are members of the immunoglobulin superfamily which have
similarly positioned cysteine residues involved in disulfide bonds.
The CD3γ, δ and ε
chains possess the immunoreceptor tyrosine-based activation motif (ITAM),
and in their cytoplasmic
region an extracellular CXXCXE
motif.