title: Nucleotide-dependent switch in proteasome assembly mediated by the Nas6 chaperone.
abstract: The proteasome is assembled via the nine-subunit lid, nine-subunit base, and 28-subunit core particle (CP). Previous work has shown that the chaperones Rpn14, Nas6, Hsm3, and Nas2 each bind a specific ATPase subunit of the base and antagonize base-CP interaction. Here, we show that the Nas6 chaperone also obstructs base-lid association. Nas6 alternates between these two inhibitory modes according to the nucleotide state of the base. When ATP cannot be hydrolyzed, Nas6 interferes with base-lid, but not base-CP, association. In contrast, under conditions of ATP hydrolysis, Nas6 obstructs base-CP, but not base-lid, association. Modeling of Nas6 into cryoelectron microscopy structures of the proteasome suggests that Nas6 controls both base-lid affinity and base-CP affinity through steric hindrance; Nas6 clashes with the lid in the ATP-hydrolysis-blocked proteasome, but clashes instead with the CP in the ATP-hydrolysis-competent proteasome. Thus, Nas6 provides a dual mechanism to control assembly at both major interfaces of the proteasome.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder, Boulder, CO 80309.
authors.forename: Frances
authors.initials: F
authors.lastname: Li
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115.
authors.forename: Geng
authors.initials: G
authors.lastname: Tian
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder, Boulder, CO 80309.
authors.forename: Deanna
authors.initials: D
authors.lastname: Langager
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder, Boulder, CO 80309.
authors.forename: Vladyslava
authors.initials: V
authors.lastname: Sokolova
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115.
authors.forename: Daniel
authors.initials: D
authors.lastname: Finley
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder, Boulder, CO 80309; soyeon.park-1@colorado.edu.
authors.forename: Soyeon
authors.initials: S
authors.lastname: Park
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D020285:Cryoelectron Microscopy; D006868:Hydrolysis; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D009711:Nucleotides / Q000737:chemistry / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding; D000072417:Protein Domains; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D018832:Molecular Chaperones; C114551:NAS6 protein, S cerevisiae; D009711:Nucleotides; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate; D046988:Proteasome Endopeptidase Complex
keywords: AAA+ ATPase; Nas6; assembly; chaperone; proteasome