Protein quality control at the inner nuclear membrane.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The nuclear envelope, comprising inner and outer membranes, regulates nuclear processes.
• Protein homeostasis at the outer nuclear membrane relies on endoplasmic-reticulum-associated protein degradation (ERAD).
• Protein quality control mechanisms at the inner nuclear membrane (INM) remain largely uncharacterized.

Purpose of the Study:

• To identify and characterize protein degradation pathways at the INM in yeast.
• To understand the role of the Asi complex in INM protein quality control.
• To identify substrates of INM and ERAD E3 ubiquitin ligases.

Main Methods:

• Utilized a genome-wide yeast library with a tandem fluorescent protein timer for unbiased screening.
• Employed genetic analysis to compare the Asi pathway with ERAD.
• Identified substrates of Asi, Hrd1, and Doa10 E3 ubiquitin ligases.

Main Results:

• Discovered a novel INM protein degradation pathway mediated by the Asi complex (Asi1 and Asi3).
• The Asi complex, with Ubc6 and Ubc7, degrades soluble and integral membrane proteins.
• Identified over 50 substrates for Asi, Hrd1, and Doa10 E3 ubiquitin ligases.
• Demonstrated that the Asi ubiquitin ligase degrades mislocalized integral membrane proteins.

Conclusions:

• The Asi complex represents a distinct but complementary pathway to ERAD for protein degradation.
• This INM-specific pathway is crucial for maintaining the integrity and identity of the inner nuclear membrane.
• The findings provide new insights into nuclear envelope protein quality control.