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A heterodimeric complex that promotes the assembly of mammalian 20S proteasomes

Nature volume 437, pages 1381–1385 (2005)Cite this article

Abstract

The 26S proteasome is a multisubunit protease responsible for regulated proteolysis in eukaryotic cells1,2. It comprises one catalytic 20S proteasome and two axially positioned 19S regulatory complexes3. The 20S proteasome is composed of 28 subunits arranged in a cylindrical particle as four heteroheptameric rings, α1–7β1–7β1–7α1–7 (refs 4, 5), but the mechanism responsible for the assembly of such a complex structure remains elusive. Here we report two chaperones, designated proteasome assembling chaperone-1 (PAC1) and PAC2, that are involved in the maturation of mammalian 20S proteasomes. PAC1 and PAC2 associate as heterodimers with proteasome precursors and are degraded after formation of the 20S proteasome is completed. Overexpression of PAC1 or PAC2 accelerates the formation of precursor proteasomes, whereas knockdown by short interfering RNA impairs it, resulting in poor maturation of 20S proteasomes. Furthermore, the PAC complex provides a scaffold for α-ring formation and keeps the α-rings competent for the subsequent formation of half-proteasomes. Thus, our results identify a mechanism for the correct assembly of 20S proteasomes.

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Figure 1: PAC1 and PAC2 associate with precursor proteasomes.
Figure 2: The PAC1–PAC2 heterodimer is rapidly degraded by proteasomes.
Figure 3: siRNA-mediated knockdown of PAC1 and PAC2 impairs proteasome assembly.
Figure 4: PAC1–PAC2 provides a scaffold for α-ring formation.

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Acknowledgements

We thank Y. Murakami for the ornithine decarboxylase degradation assay system, K. Furuyama for technical support, and D. Finley for comments on the manuscript. This work was supported by grants from the Japanese Science and Technology Agency (to S.M.), the Ministry of Education, Science and Culture of Japan (to S.M. and K.T.) and the New Energy and Industrial Technology Development Organization (to T.N.). Y.H. was supported by the Japanese Society for the Promotion of Science.

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Authors and Affiliations

  1. Laboratory of Frontier Science, Core Technology and Research Center, Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo, 113-8613, Japan

    Yuko Hirano, Hideki Yashiroda, Keiji Tanaka & Shigeo Murata

  2. Institute of Molecular Biology and Physiology, University of Copenhagen, 13 Universitetsparken, DK 2100, Copenhagen, Denmark

    Klavs B. Hendil

  3. National Institute of Advanced Industrial Science and Technology, Biological Information Research Center, Kohtoh-ku, Tokyo, 135-0064, Japan

    Shun-ichiro Iemura, Ryoichi Nagane, Yusaku Hioki & Tohru Natsume

  4. PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, 332-0012, Japan

    Shigeo Murata

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  1. Yuko Hirano
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Correspondence to Keiji Tanaka or Shigeo Murata.

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Competing interests

The sequences for human PAC1 and PAC2 have been deposited in GenBank under accession numbers BR000236 and BR000237, respectively. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

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Supplementary Figures S1–S4. (PDF 2132 kb)

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Supplementary Discussion

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Supplementary Methods

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Hirano, Y., Hendil, K., Yashiroda, H. et al. A heterodimeric complex that promotes the assembly of mammalian 20S proteasomes. Nature 437, 1381–1385 (2005). https://doi.org/10.1038/nature04106

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