An evolutionarily distinct chaperone promotes 20S proteasome α-ring assembly in plants

Area of Science:

• Molecular Biology
• Cell Biology
• Protein Biochemistry

Background:

• The 26S proteasome's core protease (CP) subcomplex is crucial for protein degradation.
• CP assembly involves sequential ring formation, starting with the alpha-ring.
• Existing chaperones like Pba1-Pba2 facilitate alpha-ring assembly in yeast.

Purpose of the Study:

• To identify novel chaperones involved in alpha-ring assembly in Arabidopsis.
• To characterize the function and interactions of the identified chaperone PBAC5.

Main Methods:

• Yeast two-hybrid screening
• Co-immunoprecipitation assays
• Analysis of Arabidopsis mutants lacking specific chaperones

Main Results:

• PBAC5 was identified as a novel alpha-ring assembly chaperone in Arabidopsis.
• PBAC5 forms a trimeric complex with PBAC1 and PBAC2 and interacts with alpha subunits.
• Arabidopsis mutants lacking PBAC5, PBAC1, or PBAC2 exhibit hypersensitivity to various stresses and proteasome assembly defects.
• PBAC5 homologs are found across diverse eukaryotic kingdoms.

Conclusions:

• PBAC5 is essential for proper alpha-ring assembly and proteasome function in Arabidopsis.
• The discovery of PBAC5 expands our understanding of proteasome biogenesis.
• PBAC5 represents a conserved component of proteasome assembly across eukaryotes.