The proteasome under the microscope: the regulatory particle in focus

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The 26S proteasome is a large protein complex responsible for regulated protein degradation in eukaryotic cells.
• While the core peptidase of the proteasome is well-characterized, the mechanism of substrate engagement and translocation by the regulatory particle remains unclear.
• Understanding the 26S proteasome is crucial for comprehending cellular protein homeostasis and disease.

Purpose of the Study:

• To review recent advancements in understanding the structure and mechanism of the 26S proteasome, particularly the regulatory particle.
• To discuss biological insights gained from recent subnanometer cryo-electron microscopy (cryo-EM) structures.
• To identify challenges in achieving atomic resolution of the entire 26S proteasome complex.

Main Methods:

• Subnanometer cryo-electron microscopy (cryo-EM) was employed to determine structures of the 26S proteasome.
• Analysis of structural data to infer mechanisms of substrate binding, ubiquitination removal, unfolding, and translocation.
• Literature review and discussion of existing knowledge and recent findings.

Main Results:

• Recent cryo-EM structures provide unprecedented views of the 19-subunit regulatory particle's architecture.
• These structures offer insights into how the regulatory particle interacts with ubiquitinated substrates.
• The ATP-dependent mechanisms for substrate unfolding and translocation are being elucidated.

Conclusions:

• Subnanometer cryo-EM has significantly advanced our understanding of the 26S proteasome's regulatory particle and substrate processing.
• Key steps in substrate delivery, including ubiquitination removal and unfolding, are better understood.
• Achieving atomic resolution of the complete 26S proteasome remains a significant technical challenge.