Protein quality control: U-box-containing E3 ubiquitin ligases join the fold

Area of Science:

• Cellular Biology
• Molecular Biology
• Biochemistry

Background:

• Molecular chaperones, including heat-shock protein 70 (Hsp70) and Hsp90, are crucial for protein folding and refolding damaged proteins.
• Protein degradation is primarily mediated by HECT and RING domain E3 ubiquitin ligases.
• The U-box protein family is emerging as a distinct class of E3 enzymes involved in protein degradation.

Purpose of the Study:

• To investigate the mechanism by which misfolded or slowly folding polypeptides are targeted for proteasomal degradation.
• To elucidate the role of co-chaperones in protein quality control pathways.
• To characterize the function of the U-box protein CHIP in conjunction with Hsp70 and Hsp90.

Main Methods:

• Investigated the interaction between molecular chaperones (Hsp70, Hsp90) and co-chaperones.
• Utilized biochemical assays to study polyubiquitination of chaperone substrates.
• Characterized the E3 ligase activity of CHIP.

Main Results:

• CHIP, a U-box protein, functions as a degradatory co-chaperone for Hsp70 and Hsp90.
• CHIP facilitates the polyubiquitination of chaperone substrates, marking them for degradation.
• Demonstrated that the interplay between chaperones and co-chaperones determines the fate of non-native proteins.

Conclusions:

• The interaction of Hsp70 and Hsp90 with co-chaperones dictates whether proteins are refolded or targeted for degradation.
• CHIP represents a key component in the protein quality control machinery, linking chaperone activity to proteasomal degradation.
• These findings establish a model where degradatory co-chaperones like CHIP play a critical role in managing non-native cellular proteins.