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Affinity Switch during Proteasome Core Particle Maturation that Regulates Pba1–Pba2 and Regulatory Particle Association
Author(s) -
Wani Prashant,
Rowland Michael,
Ondracek Alex,
Deeds Eric,
Roelofs Jeroen
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.894.3
Subject(s) - proteasome , biogenesis , proteolysis , chemistry , ubiquitin , biophysics , dimer , microbiology and biotechnology , protease , biochemistry , biology , enzyme , gene , organic chemistry
The proteasome is a large protease complex which degrades ubiquitinated proteins. It consists of a core particle (CP) that contains the proteolytic active sites and a regulatory particle (RP) that regulates substrate binding and entry into the CP. Biogenesis of the proteasome is a complex process where total 66 protein subunits needs to be precisely assembled. Nine different chaperones have been identified that are required for efficient proteasome formation. Early in CP assembly a dimer of two of these chaperones, Pba1‐Pba2, associates with immature CP. Upon CP maturation, RP replaces Pba1‐Pba2 complex. RP utilizes the same binding surface as Pba1‐Pba2 complex and it is not clear how the RP and Pba1‐Pba2 binding to CP is regulated. Our biochemical purifications showed that immature CP prefers Pba1‐Pba2 and binds tightly, hence preventing early association of RP to immature CP. Analysis of reconstitution assays and kinetic data indicated that CP undergoes changes during maturation resulting reduced binding affinity of Pba1‐Pba2 for mature CP and increased binding affinity of RP for mature CP. Mathematical modeling indicates that this “affinity switch” mechanism has likely evolved to improve assembly efficiency by preventing the formation of stable, non‐productive intermediates. Our work thus provides mechanistic insights into a crucial step in proteasome biogenesis. Research Support: COBRE‐PSF, KINBRE, NSF.