Reconfiguration of the proteasome during chaperone-mediated assembly.

ABSTRACT: The proteasomal ATPase ring, comprising Rpt1-Rpt6, associates with the heptameric ?-ring of the proteasome core particle (CP) in the mature proteasome, with the Rpt carboxy-terminal tails inserting into pockets of the ?-ring. Rpt ring assembly is mediated by four chaperones, each binding a distinct Rpt subunit. 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 ?-pockets with poor specificity, except for Rpt6, which uniquely bound the ?2/?3-pocket. Although the Rpt6 tail is not visualized within an ?-pocket in mature proteasomes, it inserts into the ?2/?3-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.

SUBMITTER: Park S 

PROVIDER: S-EPMC3687086 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature