The proteasomal ATPase ring, comprising Rpt1–Rpt6, associates with the heptameric α-ring of the proteasome core particle (CP) in the mature proteasome, with the Rpt carboxy-terminal tails inserting into pockets of the α-ring1,2,3,4. Rpt ring assembly is mediated by four chaperones, each binding a distinct Rpt subunit5,6,7,8,9,10. 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 α-pockets with poor specificity, except for Rpt6, which uniquely bound the α2/α3-pocket. Although the Rpt6 tail is not visualized within an α-pocket in mature proteasomes2,3,4, it inserts into the α2/α3-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.
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Electron Microscopy Data Bank
Protein Data Bank
Data have been deposited in the Electron Microscopy Data Bank under the following accession numbers: free CP, EMD-5593; Rpt1–CP, EMD-5611; Rpt2–CP, EMD-5612; Rpt3–CP, EMD-5613; Rpt4–CP, EMD-5614; Rpt5–CP, EMD-5615; Rpt6–CP, EMD-5616; and base1–CP: EMD-5617. For the crystal structures, data have been deposited in the Protein Data Bank under accessions 4FP7 (Hsm3) and 4JPO (Hsm3–Rpt1 C domain).
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We thank M. Schmidt, T. Walz, C. Chen, and Finley laboratory members for suggestions, and C. Mann for antibodies. This work was supported in part by grants from the National Institutes of Health (NIH; R01GM082893 and 1S10RR026814-01), the University of California San Francisco Program for Breakthrough Biomedical Research (New Technology Award) to Y.C.; the Johnson Cancer Research Center, the National Center for Research Resources (5P20RR017708 and P20 RR016475) and NIH (8 P20 GM103420 and P20 GM103418) to J.R.; and grants from the NIH to P.C. (R01GM045335) and D.F. (R37GM043601). S.P. was supported by the Charles A. King Trust Postdoctoral Research Fellowship Program of the Medical Foundation. Use of IMCA-CAT was supported by the Industrial Macromolecular Crystallography Association though a contract with the Hauptman-Woodward MRI. Use of the Advanced Photon Source was supported by the US Department of Energy (contract no. DE-AC02-06CH11357).
The authors declare no competing financial interests.
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Park, S., Li, X., Kim, H. et al. Reconfiguration of the proteasome during chaperone-mediated assembly. Nature 497, 512–516 (2013) doi:10.1038/nature12123
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