Substrate structure determines p97- and RAD23A/B-mediated proteasomal degradation in human cells.

Area of Science:

• Cellular Biology
• Biochemistry
• Molecular Mechanisms of Protein Degradation

Background:

• Proteasomal degradation of ubiquitinated proteins is crucial for cellular homeostasis.
• Accessory factors like p97 and shuttle factors (e.g., RAD23A/B) are involved, but their precise roles and substrate-specific requirements remain unclear.
• Understanding these factors is key to developing targeted protein degradation therapies.

Purpose of the Study:

• To investigate how substrate structural properties influence the requirement for p97 and RAD23A/B in proteasomal degradation in human cells.
• To elucidate the relationship between substrate structure, ubiquitination, and the involvement of specific degradation machinery.

Main Methods:

• Utilized two distinct ubiquitin-fusion model substrates: well-folded Ub-GFP and unstructured Ub-GFP-tail.
• Performed interactome analyses to identify protein binding partners.
• Conducted knockdown experiments of RAD23A/B to assess degradation dynamics.
• Analyzed ubiquitin chain composition and length.

Main Results:

• Substrate structure dictates dependency on p97 and RAD23A/B for degradation.
• Well-folded Ub-GFP requires p97 and RAD23A/B, while Ub-GFP-tail bypasses them.
• Ub-GFP-tail shows stronger binding to the proteasome, whereas Ub-GFP interacts more with p97 and RAD23B.
• RAD23A/B knockdown impaired Ub-GFP degradation but not Ub-GFP-tail degradation.

Conclusions:

• Protein structure is a critical determinant of accessory factor requirements in the proteasomal degradation pathway.
• Targeted protein degradation strategies can be refined by considering substrate structural features.
• This study provides insights into the differential engagement of degradation machinery based on substrate conformation.