Stoichiometry of the T-cell receptor-CD3 complex and key intermediates assembled in the endoplasmic reticulum.

The T-cell receptor (TCR)-CD3 complex is critical for T-cell development and function, and represents one of the most complex transmembrane receptors. Models of different stoichiometry and valency have been proposed based on cellular experiments and these have important implications for the mechanisms of receptor triggering. Since determination of receptor stoichiometry in T-cells is not possible due to the presence of previously synthesized, unlabeled receptor components with different half-lives, we examined the stoichiometry of the receptor assembled in endoplasmic reticulum (ER) microsomes of B-cell origin. The stoichiometric relationship among all subunits was directly determined using intact radiolabeled TCR-CD3 complexes that were isolated with a sequential, non-denaturing immunoprecipitation method, and identical results were obtained with two detergents belonging to different structural classes. The results firmly establish that the alphabeta TCR-CD3 complex assembled in the ER is monovalent and composed of one copy of the TCRalphabeta, CD3deltaepsilon, CD3gammaepsilon and zeta-zeta dimers.