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 ? ring (?1-?7) of the CP via the Rpt C-terminal tails individually binding to the ? 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 ?3-Rpt6 tail and ?2-Rpt3 tail interactions in the proteasome, decreased ?3-Rpt6 tail interaction facilitates robust ?2-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.

SUBMITTER: Sokolova V 

PROVIDER: S-EPMC4598862 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature