Substrate Insolubility Dictates Hsp104-Dependent Endoplasmic-Reticulum-Associated Degradation

Area of Science:

• Cell Biology
• Protein Degradation
• Molecular Chaperones

Background:

• Misfolded proteins in the endoplasmic reticulum (ER) are degraded via ER-associated degradation (ERAD).
• The initial selection mechanism for ERAD substrates is not well understood.
• Understanding substrate selection is crucial for controlling protein homeostasis.

Purpose of the Study:

• To investigate the selection process of misfolded proteins for ERAD.
• To identify factors influencing ERAD substrate selection.
• To elucidate the role of chaperones in ERAD substrate selection.

Main Methods:

• Constructed a series of protein truncations in an ER-tethered domain to study ERAD substrate selection.
• Assessed degradation rates of truncated proteins.
• Analyzed the correlation between substrate instability, detergent insolubility, and ERAD.
• Investigated the role of Hsp104 in the degradation of insoluble protein species.

Main Results:

• ERAD substrate instability positively correlated with detergent insolubility, indicating selection of aggregation-prone species.
• Hsp104 facilitated the degradation of insoluble protein aggregates.
• Retrotranslocation of ubiquitinated substrates from the ER was impaired without Hsp104.
• Chaperone-mediated selection removes potentially toxic, aggregation-prone proteins from the ER membrane.

Conclusions:

• Aggregation-prone proteins are selected for ER-associated degradation (ERAD).
• The chaperone Hsp104 plays a critical role in selecting and degrading these aggregation-prone ERAD substrates.
• Chaperone-mediated selection prevents the accumulation of toxic protein species in the ER.