Disulfide linkage of the ζ and η chains of the T cell receptor. Possible identification of two structural classes of receptors

The T cell antigen receptor (TCR) is a multisubunit membrane complex. It consists of two disulfide-linked polymorphic chains (either α-β or γ-δ heterodimers) which are noncovalently linked to five invariant chains. The CD3-γ and CD3-δ chains bear N-linked carbohydrates and the CD3-ε and ζ chains are nonglycosylated. Further analysis of the ζ chain in murine T cells demonstrates that it can exist as either a homodimer or disulfide linked to an additional protein with an apparent M(r) of 22,000. The partial peptide map of this 22-kDa protein is different than ζ and all of the CD3 components. Like ζ, it has no apparent N-linked carbohydrate chains. We have chosen to refer to this subunit as the η chain of the TCR. Ninety percent of ζ in cloned and nonclonal populations of T cells exist as a homodimer, and the remainder is found linked to the η chain. The tight regulation of the ζ-ζ to ζ-η ratio suggests an important functional role for these structural components of the TCR.