Role of intramembrane charged residues in the quality control of unassembled T-cell receptor α-chains at the endoplasmic reticulum

摘要

Endoplasmic reticulum (ER)-associated degradation (ERAD) of unassembled T-cell receptor α-chain (TCRα) is reliant on the presence of two basic residues in the transmembrane (TM) segment of TCRα. The precise role of these residues in ER quality control is unclear. Here, we show that a TCRα mutant lacking these intramembrane charged residues has a tendency to form homooligomers through an interchain disulfide bond that involves a specific pair of cysteine residues. Covalent oligomerization of TCRα appears to stabilize it at the ER membrane. The presence of a single lysine residue at specific positions within the TCRα TM domain abolishes its oligomerization and causes its rapid degradation. Conversely, when TCRα oligomerization is induced by a bivalent compound, the degradation of TCRα is inhibited. Together, these results suggest that the intramembrane charged residues in TCRα do not function as a signal for substrate recognition in ERAD. Instead, their primary role is to reduce TCRα oligomerization, maintaining it in a retrotranslocation-competent state. Our results also suggest that the ERAD machinery is inefficient when coping with oligomerized substrates, indicating a requirement for chaperone-mediated protein disassembly in the ER lumen prior to retrotranslocation.