Structural basis of human 20S proteasome biogenesis

Area of Science:

• Molecular Biology
• Structural Biology
• Cellular Biology

Background:

• Proteasomes are essential cellular machines that degrade proteins, preventing the buildup of toxic substances.
• The formation of the 20S core complex requires the coordinated action of five chaperones: PAC1-4 and POMP.

Purpose of the Study:

• To elucidate the structural mechanisms by which chaperones facilitate human proteasome assembly.
• To provide a molecular blueprint for the biogenesis of the 20S proteasome core particle.

Main Methods:

• Endogenous chaperone tagging using CRISPR/Cas gene editing.
• Cryo-electron microscopy (cryo-EM) to analyze chaperone-bound complexes.
• Structural analysis of proteasome assembly intermediates.

Main Results:

• Identified an early α-ring intermediate stabilized by PAC1-4.
• Observed a transition to β-ring assembly involving PAC3/PAC4 dissociation and PAC1 rearrangement.
• Demonstrated that β-ring completion and dimerization trigger pro-peptide cleavage, leading to POMP and PAC1/PAC2 dissociation and mature 20S proteasome formation.

Conclusions:

• The study reveals critical structural insights into the human proteasome assembly pathway.
• A molecular model for 20S proteasome biogenesis is provided, highlighting key chaperone roles and structural transitions.