Proteasome assembly from 15S precursors involves major conformational changes and recycling of the Pba1–Pba2 chaperone

• Published in: Nature communications Vol. 6; no. 1; p. 6123
• Main Authors: Kock, Malte, Nunes, Maria M., Hemann, Matthias, Kube, Sebastian, Jürgen Dohmen, R., Herzog, Franz, Ramos, Paula C., Wendler, Petra
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.01.2015; Nature Publishing Group
• Subjects: 13/51; 631/45/474/2085; 631/45/612/1981; 82/29; 82/80; 82/83; Cross-Linking Reagents - chemistry; Dimerization; Humanities and Social Sciences; Mass Spectrometry; Microscopy, Electron; Molecular Chaperones - metabolism; multidisciplinary; Proteasome Endopeptidase Complex - chemistry; Proteasome Endopeptidase Complex - metabolism; Protein Binding; Protein Conformation; Protein Structure, Secondary; Protein Structure, Tertiary; Protein Subunits - metabolism; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - metabolism; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms7123

The chaperones Ump1 and Pba1–Pba2 promote efficient biogenesis of 20S proteasome core particles from its subunits via 15S intermediates containing alpha and beta subunits, except beta7. Here we elucidate the structural role of these chaperones in late steps of core particle biogenesis using biochemical, electron microscopy, cross-linking and mass spectrometry analyses. In 15S precursor complexes, Ump1 is largely unstructured, lining the inner cavity of the complex along the interface between alpha and beta subunits. The alpha and beta subunits form loosely packed rings with a wider alpha ring opening than in the 20S core particle, allowing for the Pba1–Pba2 heterodimer to be partially embedded in the central alpha ring cavity. During biogenesis, the heterodimer is expelled from the alpha ring by a restructuring event that organizes the beta ring and leads to tightening of the alpha ring opening. In this way, the Pba1–Pba2 chaperone is recycled for a new round of proteasome assembly. The barrel-shaped 20S proteasome core particle assembles via 15S intermediates through the action of Ump1 and Pba1–Pba2 chaperones. Using structural approaches, Kock et al . reveal conformational changes occurring upon formation of the nascent 20S particle leading to ejection of Pba1–Pba2.