Colocalized transmembrane determinants for ER degradation and subunit assembly explain the intracellular fate of TCR chains.

The intracellular fate of T cell antigen receptor (TCR) subunits (alpha beta gamma delta epsilon zeta 2) is determined by their assembly in the endoplasmic reticulum (ER). To study the structural bases for this tight correlation between assembly and intracellular fate, we sought to define the nature of determinants for both ER degradation and subunit assembly within the TCR-alpha chain. We found that a 9 amino acid transmembrane sequence of the TCR-alpha chain, containing 2 critical charged residues, was sufficient to cause ER degradation when placed in the context of the Tac antigen, used here as a reporter protein. CD3-delta assembled with chimeric proteins containing this short transmembrane sequence, and this assembly resulted in abrogation of targeting for ER degradation. Thus, the colocalization of determinants for ER degradation and sites of subunit interactions explains how the fate of some newly synthesized TCR chains can be decided on the basis of their assembly status.