ERAD and protein import defects in a sec61 mutant lacking ER-lumenal loop 7

Area of Science:

• Cellular Biology
• Protein Translocation
• Endoplasmic Reticulum Biology

Background:

• The Sec61 channel is crucial for protein transport across the endoplasmic reticulum (ER) membrane.
• Its role in secretory protein biogenesis and ER-associated degradation (ERAD) is established.
• The function of the ER-lumenal loop 7 (L7) in channel gating remains unclear.

Purpose of the Study:

• To investigate the role of Sec61p's ER-lumenal loop 7 (L7) in protein translocation and ERAD.
• To elucidate the mechanism of Sec61 channel opening for different translocation modes.

Main Methods:

• Utilized yeast models to study the Y345H mutation in L7 and complete L7 deletion (sec61∆L7).
• Assessed protein import into the ER, ERAD of soluble and membrane proteins.
• Analyzed Sec61 channel stability, co-translational protein integration, and Sec complex formation.

Main Results:

• The Y345H mutation caused delayed misfolded protein export but no ER import defects in yeast.
• Sec61∆L7 yeast exhibited hypersensitivity to cold and tunicamycin, with severe defects in soluble protein import and ERAD.
• Membrane protein ERAD and co-translational integration were largely unaffected in sec61∆L7.

Conclusions:

• Sec61p's L7 is essential for initiating posttranslational soluble protein import into the ER.
• L7 plays a critical role in the export of misfolded soluble proteins from the ER.
• These findings suggest L7 is key for the transverse gating of the Sec61 channel.