Reconfiguration of the proteasome during chaperone-mediated assembly

• Published in: Nature (London) Vol. 497; no. 7450; pp. 512 - 516
• Main Authors: Park, Soyeon, Li, Xueming, Kim, Ho Min, Singh, Chingakham Ranjit, Tian, Geng, Hoyt, Martin A., Lovell, Scott, Battaile, Kevin P., Zolkiewski, Michal, Coffino, Philip, Roelofs, Jeroen, Cheng, Yifan, Finley, Daniel
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 23.05.2013; Nature Publishing Group
• Subjects: 631/45; 631/535/1258; Adenosine triphosphatase; Adenosine Triphosphatases - chemistry; Adenosine Triphosphatases - genetics; Adenosine Triphosphatases - metabolism; Adenosine Triphosphate - metabolism; ATPases; Binding Sites; Brewer's yeast; Carrier Proteins - metabolism; Cryoelectron Microscopy; Enzymes; Holoenzymes - chemistry; Holoenzymes - metabolism; Humanities and Social Sciences; Hydrolysis; letter; Models, Molecular; Molecular chaperones; Molecular Chaperones - metabolism; multidisciplinary; Peptides; Physiological aspects; Proteasome Endopeptidase Complex - chemistry; Proteasome Endopeptidase Complex - genetics; Proteasome Endopeptidase Complex - metabolism; Protein Conformation; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - growth & development; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - chemistry; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Science; Ubiquitin; Ubiquitin-proteasome system; Yeast; United States
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature12123

The proteasome degrades ubiquitin-conjugated substrates; here, structural and functional insights from studies in yeast reveal that it is reconfigured during chaperone-mediated assembly. Proteasome structure and function The proteasome is a protein complex that degrades ubiquitin-conjugated substrates. The 26S proteasome consists of a core particle (CP) and a regulatory particle (RP) formed of a base and lid. In this study, Daniel Finley and colleagues present structural and functional insights into the assembly of the base–CP complex. The proteasomal ATPase ring, comprising Rpt1–Rpt6, associates with the heptameric α-ring of the proteasome core particle (CP) in the mature proteasome, with the Rpt carboxy-terminal tails inserting into pockets of the α-ring 1 , 2 , 3 , 4 . Rpt ring assembly is mediated by four chaperones, each binding a distinct Rpt subunit 5 , 6 , 7 , 8 , 9 , 10 . Here we report that the base subassembly of the Saccharomyces cerevisiae proteasome, which includes the Rpt ring, forms a high-affinity complex with the CP. This complex is subject to active dissociation by the chaperones Hsm3, Nas6 and Rpn14. Chaperone-mediated dissociation was abrogated by a non-hydrolysable ATP analogue, indicating that chaperone action is coupled to nucleotide hydrolysis by the Rpt ring. Unexpectedly, synthetic Rpt tail peptides bound α-pockets with poor specificity, except for Rpt6, which uniquely bound the α2/α3-pocket. Although the Rpt6 tail is not visualized within an α-pocket in mature proteasomes 2 , 3 , 4 , it inserts into the α2/α3-pocket in the base–CP complex and is important for complex formation. Thus, the Rpt–CP interface is reconfigured when the lid complex joins the nascent proteasome to form the mature holoenzyme.