title: Proteasome Activation is Mediated via a Functional Switch of the Rpt6 C-terminal Tail Following Chaperone-dependent Assembly.
abstract: In the proteasome, the proteolytic 20S core particle (CP) associates with the 19S regulatory particle (RP) to degrade polyubiquitinated proteins. Six ATPases (Rpt1-Rpt6) of the RP form a hexameric Rpt ring and interact with the heptameric α ring (α1-α7) of the CP via the Rpt C-terminal tails individually binding to the α subunits. Importantly, the Rpt6 tail has been suggested to be crucial for RP assembly. Here, we show that the interaction of the CP and Rpt6 tail promotes a CP-Rpt3 tail interaction, and that they jointly mediate proteasome activation via opening the CP gate for substrate entry. The Rpt6 tail forms a novel relationship with the Nas6 chaperone, which binds to Rpt3 and regulates the CP-Rpt3 tail interaction, critically influencing cell growth and turnover of polyubiquitinated proteins. CP-Rpt6 tail binding promotes the release of Nas6 from the proteasome. Based on disulfide crosslinking that detects cognate α3-Rpt6 tail and α2-Rpt3 tail interactions in the proteasome, decreased α3-Rpt6 tail interaction facilitates robust α2-Rpt3 tail interaction that is also strongly ATP-dependent. Together, our data support the reported role of Rpt6 during proteasome assembly, and suggest that its function switches from anchoring for RP assembly into promoting Rpt3-dependent activation of the mature proteasome.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology University of Colorado, Boulder, CO 80309.
authors.forename: Vladyslava
authors.initials: V
authors.lastname: Sokolova
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology University of Colorado, Boulder, CO 80309.
authors.forename: Frances
authors.initials: F
authors.lastname: Li
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology University of Colorado, Boulder, CO 80309.
authors.forename: George
authors.initials: G
authors.lastname: Polovin
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology University of Colorado, Boulder, CO 80309.
authors.forename: Soyeon
authors.initials: S
authors.lastname: Park
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D015151:Immunoblotting; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D057149:Ubiquitinated Proteins / Q000378:metabolism
chemical_list: D018832:Molecular Chaperones; C114551:NAS6 protein, S cerevisiae; C521692:Rpt3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D057149:Ubiquitinated Proteins; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C069670:RPT6 protein, S cerevisiae